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vascular

vascular

vascular Sentence Examples

  • The vascular tissue is typically separable into distinct collateral bundles (figs.

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  • The root differs from the shoot in the characters of its surface tissues, in the absence of the green assimilative pigment chlorophyll, in the arrangement of its vascular system and in the mode of growth at the apex, all features which are in direct relation to its normally subterranean life and its fixative and absorptive functions.

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  • This is especially the case in the young vascular bundles themselves (desmogen strands).

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  • This is especially the case in the young vascular bundles themselves (desmogen strands).

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  • In such cases the vascular system is said to be polycyclic in contrast with the ordinary monocyclic condition, These internal strands or cylinders are to be regarded as peculiar types of elaboration of the stele, and probably act as reservoirs for water-storage which can be drawn upon when the water supply from the root is deficient.

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  • Such a vascular cylinder is called a haplostele, and the axis containing it is said to be haplostelic. In the stele of the root the strands of tracheids along the lines where the xylem touches the pericycle are spiral or annular, and are the xylem elements first formed when the cylinder is developing.

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  • The vascular supply of the leaf (leaf-trace) consists of a single strand only in the haplostelic and some of the more primitive siphonostelic forms. In the microphyllous groups Leaf.trace of Pteridophytes (Lycopodiales and Equisetales) in and Petlolar which the leaves are small relatively to the stem, the Strands, single bundle destined for each leaf is a small strand whose departure causes no disturbance in the cauline stele.

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  • In higher forms the conducting strands of the leaves are continued downwards into the stem, and eventually come into connection with the central hydrom cylinder, forming a complete cylindrical investment apparently distinct from the latter, and exhibiting a differentiation into hydrom, leptom and amylom which almost completely parallels that found among the true vascular plants.

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  • In higher forms the conducting strands of the leaves are continued downwards into the stem, and eventually come into connection with the central hydrom cylinder, forming a complete cylindrical investment apparently distinct from the latter, and exhibiting a differentiation into hydrom, leptom and amylom which almost completely parallels that found among the true vascular plants.

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  • It is essentially a living tissue, and serves to place all the living cells of the secondary vascular tissues in communication.

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  • In the Vascular Plants this tissue is collectively known as the vascular system.

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  • The body of a vascular plant is developed in the first place by repeated division of the fertilized egg and the growth of Develop- the products of division.

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  • The tissue-elements just described are found only in the more complicated secondary vascular tissues of certain Dicotyledons.

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  • In one type they may take the form of specially-modified single epidermal cells or multicellular hairs without any direct connection with the vascular system.

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  • In one type they may take the form of specially-modified single epidermal cells or multicellular hairs without any direct connection with the vascular system.

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  • But these two principles do not find their full expression till we come, in the ascending series, to the Vascular Plants.

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  • Later, the axis branches by the formation of new growing-points, and in this way the complex system of axes forming the body of the ordinary vascular plant is built up. In the flowering plants the embryo, after developing up to a certain point, stopf growing and rests, enclosed within the seed.

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  • The surface layer of the rhizome bears rhizoids, and its whole structure strikingly resembles that of the typical root of a vascular plant.

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  • In other cases the leaf-gaps are very broad and long, the meristeles separating them being reduced to comparatively slender strands, while there is present in each gap a network of fine vascular threads, some of which run out to the leaf, while others form cross-connections between these leaf-trace strands and also with the main cauline meristeles.

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  • In many Pteridophytes thi first leaf is formed very early, and the first vascular strand i!

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  • The stelar system of Vascular Plants has no direct phylogenetic connection with that of the mosses.

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  • In the blade of a typical leaf of a vascular plantessentially a thin plate of assimilating tissuethe vascular system takes the form of a number of separate, usually branching and anastomosing strands.

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  • In this case also the differentiation of leaf-bundles, which typically begins at the base of the leaf and extends upwards into the leaf and downwards into the stem, is the first phenomenon in the development of vascular tissue, and is seen at a higher level than the formation of a stele.

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  • In some forms other gaps (perforations) appear in the vascular tube placing the pith and cortex in communication.

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  • In some solenostelic ferns, and in many dictyostelic ones additional vascular strands are present which do not form part of the primary vascular tube.

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  • The differentiation of the stelar stereom, which usually takes the form of a sclerized pericycle, and may extend to the endocycle and parts of the rays, takes place in most cases later than the formation of the primary vascular strand.

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  • Sometimes a complete internal vascular cylinder, having the same structure as the primary one, and concentric with it, occurs in the pith, and others may appear, internal to the first (Matonia, Saccoloma).

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  • The periblem, one cell thick at the apex, produces the cortex, to which the piliferous layer belongs in Monocotyledons; and the plerome, which is nearly always sharply separated from the periblem, gives rise to the vascular cylinder.

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  • Thi vascular system is connected in various ways with that of th(parent axis by the differentiation of bundle-connections across thi cortex of the latter.

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  • A considerable evolution in complexity can be traced in passing from the simplest forms of xylem and phloem found in the primary vascular tissues both among Pteridophytes and Phanerogams to these highly differentiated types.

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  • In general structure they approach the Phanerogams with which they form collectively the Vascular Plants as contrasted with the Cellular PlantsThallophyta and Bryophyta.

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  • The type of siphonostele characteristic of many ferns, in which are found internal phloem, and an internal endodermis separating the vascular conjunctive from the pith is known as a solenostele.

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  • The main feature is the development of special vascular stereom and storage tissue.

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  • In the very frequent cases where the bundles have considerable individuality, the fibrous pericyclic cap very clearly has a common origin from the same strand of tissue as the vascular elements themselves.

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  • In the very frequent cases where the bundles have considerable individuality, the fibrous pericyclic cap very clearly has a common origin from the same strand of tissue as the vascular elements themselves.

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  • In many forms its hyphae are particularly thick-walled, and may strikingly resemble the epidermis of a vascular plant.

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  • ft1.Types of Stole in Vascular Plants.

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  • The splitting up of the vascular tube I into separate strands does not depend wholly upon the occurrence I of leaf-gaps.

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  • i&Vertical section of a Palm-stem showing the root as it is found in most Pteridophytes vascular bundle,, Jr. curving and many Phanerogams has been already inwards and then outwards.

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  • The radial structure is characteristic of all root-steles, which have in essential points a remarkably uniform structure throughout the vascular plants, a fact no doubt largely dependent on the very uniform conditions under which they live.

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  • The sporophyte is the plant which is differentiated into stem, leaf and root, which show a wonderful variety 01 form; the internal structure also shows increased complexity and variety as compared with the other group of vascular plants, the Pteridophyta.

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  • Where a large-celled pith is developed this often becomes obvious very early, and in some cases it appears to have separate initials situated below those of the hollow vascular cylinder.

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  • Every great group or phylum of vascular plants, when it has become dominant in the vegetation of the world, has produced members with the tree habit arising by the formation of a thick woody trunk, in most cases by the activity of a cambium.

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  • This observation led him to further work, and he succeeded in showing that in vascular organs the presence of cells in inflammatory exudates is not the result of exudation but of multiplication of pre-existing cells.

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  • Outside this are three arcs of large cells showing characters typical of the endodermis in a vascular plan.t; these are interrupted by strands ofnarrow, elongated, thick-walled cells, which send branches into the little brown scales borne by the rhizome.

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  • The body of the sporophyte in the great majority of the vascular plants shows a considerable increase in complexity over that found in the gametophyte of Bryophytes.

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  • The structure of the stomata of the sporophyte of vascular plants is fundamentally the same as that of the stomata on the sporogonium of the true mosses and of the liverwort A nihoceros.

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  • The structure of the stomata of the sporophyte of vascular plants is fundamentally the same as that of the stomata on the sporogonium of the true mosses and of the liverwort A nihoceros.

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  • In the stems of many water-plants various stages of reduction of the vascular system, especially of the xylem, are met with, and very often this reduction leads to the formation of a compact stele in which the individuality of the separate Reduced bundles may be suppressed, so that a closed cylinder lmpbost~h1c of xylem surrounds a pith.

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  • In the stems of many water-plants various stages of reduction of the vascular system, especially of the xylem, are met with, and very often this reduction leads to the formation of a compact stele in which the individuality of the separate Reduced bundles may be suppressed, so that a closed cylinder lmpbost~h1c of xylem surrounds a pith.

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  • The evolution of the vascular structure of the petiole in the higher ferns is strikingly parallel with that of the stem, except in some few special cases.

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  • The viscid pulp soon hardens, affording a protection to the seed; in germination the sucker-root penetrates the bark, and a connexion is established with the vascular tissue of the first plant.

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  • There is good reason to believe that the haplostele is primitive in the evolution of the vascular system.

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  • The typical structure of the vascular cylinder of the adult primary stem in the Gyrnnosperms and Dicotyledons is, like that of the higher ferns, a hollow cylinder of vas- Structure of cular tissue enclosing a central parenchymatous pith.

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  • In the megaphyllous forms, on the other hand, (Ferns) whose leaves are large relatively to the stem, the departure of the correspondingly large trace causes a gap (leaf-gap) in the vascular cylinder, as already described.

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  • One of the most striking characters common to the two highest groups of plants, the Pteridophytes and Phanerogams, is the Vascular possession of a double (hydrom-leptom) conducting .s system, such as we saw among the highest mosses, YS em.

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  • c eun~7 Such an arrangement of vascular tissue is called radial, ~

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  • It is confined to the sporophyte, which forms the, leafy plant in these groups, and is known as the vascular system.

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  • For this reason a stem in which as pot ystelic, the term stele being transferr~d from the primary I central cylinder of the i~xis and applied to the vascular strands just described.

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  • In some cases special secreting tissues, resin ducts, oil glands, laticiferous tissue, crystal sacs, &c., may be developed among the ordinary secondary vascular elements.

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  • When the vascular tissue of such plants is arranged Camblum in separate bundles these are said to be closed.

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  • Sometimes the original cambial ring is broken into several arcs, each of which is completed into an independent circle, so that several independent secondary vascular cylinders are formed.

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  • Opposite the primary xylems, the cambium either (a) forms parenchyma on both sides, making a broad, secondary (principal) ray, which interrupts the vascular ring and is divided at its inner extremity by the islet of primary xylem; or (b) forms secondary xylem and phloem in the ordinary way, completing the vascular ring.

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  • Thus the structure of an old thickened root approximates to that of an old thickened stem, and so far as the vascular tissue is concerned can often only be distinguished from the latter by the position and orientation of the primary xylems. The cambium of the primary root, together with the tissues which it forms, is always directly continuous with that of the primary stem, just in the same way as the tissues of the primary stele.

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  • In nearly all plants which produce secondary vascular tissues by means of a cambium there is another layer of secondary meristem arising externally to, but in quite the same fashion as, Ph II

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  • supplementary vascular bundles, anomalous cambial zones, &c. It is often enormously developed and forms a very important tissue in roots.

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  • The new work largely centred round a discussion of the nature and origin of vessels, conspicuous features in young plant tissues which thus acquired an importance in the contemporary literature out of proportion to their real significance in the construction of the vascular plant.

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  • The increasing development of the wood as the tree grows older is largely due to the demands for the conduction of water and mineral matters dissolved in it, which are made by the increased number of leaves which from year to year it bears, and which must each be put into communication with the central mass by the formation of new vascular bundles.

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  • After making its way into the interior, the intruder sets up a considerable hyper trophy of the tissue, causing the formation of a tubercle, which soon shows a certain differentiation, branches of the vascular bundles of the root being supplied to it.

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  • They are supplied with a regular system of conducting vascular bundles communicating with those of the roots.

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  • In the vascular cryptogams and phanerogams it takes place in the spore mother cells and the reduced number is found in all the cells of the gametophyte, the full number in those of the sporophyte.

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  • In Monoblepliaris, one of the lower Fungi, in some Algae, in the Vascular Cryptograms, in Cycads (Zamia and Cycas), and in Ginkgo, an isolated genus of Gymnosperms, the male cell is a motile spermatozoid with two or more cilia.

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  • In the Characeae, the Vascular Cryptogams, in Zamia and Cycas, and in Ginkgo, the spermatozoids are more or less highly modified cells witi+m.-S, ~..

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  • At the an ~ ~ tenor end are attached - two cilia or flagella In, , C the Vascular Cryptogams -- ~ the structure is much the;il ~.: -; same, but a more or less ~ ~ ~ spherical mass of cyto 4 i~- - ~ plasm remains attached .8 ~ :~ to the posterior spirals, -.

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  • In the spermatozoids of Chara, Vascular Cryptogams, and in those of Cycas, Zamia and Ginkgo, the cilia arise from a centrosome-like body which is found on one side of the nucleus of the spermatozoid mother-cell.

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  • It was characterized by arborescent vascular Cryptogams and Gymnosperms of a type (Cordaiteae) which have left no descendants beyond it.

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  • Both were in turn replaced by the Lower Mesozoic flora, which again is thought to have had its birth in the hypothetical Gondwana land, and in which Gymnosperms played the leading part formerly taken by vascular Cryptogams. The abundance of Cycadean plants is one of its most striking features.

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  • Internally they are found to consist of a lamina twisted upon itself, and externally they generally exhibit a tortuous structure, produced, before the cloaca was reached, by the spiral valve of a compressed small intestine (as in skates, sharks and dog-fishes); the surface shows also vascular impressions and corrugations due to the same cause.

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  • From near the entrance of the optic nerve, through the original choroidal fissure, arises the much-folded pecten, deeply pigmented and very vascular, far into the vitreous humour.

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  • Vascular System.

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  • The arrangement of the conducting tissue in the stem is characteristic; a transverse section of the very young stem shows a nunber of distinct conducting strands - vascular bundles - arranged in a ring round the pith; these soon become united to form a closed ring of bast and wood, separated by a layer of formative tissue (cambium).

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  • Thus in the Chaetopoda the perivisceral cavity is coelomic; in this respect the group contrasts with the Arthropoda and Molluscs, where the perivisceral cavity is, mainly at least, part of the vascular or haemal system, and agrees with the Vertebrata.

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  • This is the vascular or haemal system (formerly and unnecessarily termed pseudhaemal).

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  • With a few exceptions among the Polychaeta the vascular system is always present among the Chaetopoda, and always consists of a system of vessels with definite walls, which rarely communicate with the coelom.

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  • The main trunks of the vascular system often possess valves at the origin of branches which regulate the direction of the blood flow.

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  • The vascular system is in the majority of Chaetopods a closed system.

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  • Goodrich), that among the Hirudinea the coelom, which is largely broken up into narrow tubes, may be confluent with the tubes of the vascular system.

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  • In the case of many Oligochaeta where there is no vascular network surrounding the nephridium, this function must be the chief one of those glands, the more elaborate process of excretion taking place in the case of nephridia surrounded by a rich plexus of blood capillaries.

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  • Vascular system generally present forming a closed system of tubes.

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  • Vascular and 8, 8 and 9, the oviducal pores system always present, upon the 14th and the male pores forming a closed system, upon the 18th segment.

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  • The vascular system is simple with as a rule direct communication between dorsal and ventral vessels in each segment.

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  • Sperm ducts and atria as in Limicolae; egg sacs large; body wall thick; vascular system and nephridia as in Terricolae.

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  • Vascular system complicated without regular connexion between dorsal and ventral vessels, except in anterior segments.

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  • Nephridia as a rule with abundant vascular supply.

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  • The vascular system is as in the lower Oligochaeta.

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  • Coelom generally reduced to a system of tubes, sometimes communicating with vascular system; in Acanthobdella and Ozobranchus a series of metamerically arranged chambers as in Oligochaeta.

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  • Neither in this genus nor in the last is there any communication between coelom and vascular system.

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  • Goodrich that the vascular system and the coelom are in communication (as in vertebrates by means of the lymph system).

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  • On the other hand, it has been held that in these leeches there is no vascular system at all and that the entire system of spaces is coelom.

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  • In favour of regarding the vascular system as totally absent, is the fact that the median coelomic channels contain no dorsal and ventral vessel.

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  • In favour of seeing in the lateral trunks and their branches a vascular system, is the contractility of the former, and the fact of the intrusion of the latter into the epidermis, matched among the Oligochaeta, where undoubted blood capillaries perforate the epidermis.

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  • The vascular system is not extensive, the arteries soon ending in the well-marked spongy tissue which builds up the muscular foot, parapodia, and dorsal body-wall.

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  • The body-cavity and the muscular, fibrous and vascular tissues are traced partly to two symmetrically disposed " mesoblasts," which bud off from the invaginated arch-enteron, partly to cells derived from the ectoderm, which at a very early stage is connected by long processes with the invaginated endoderm.

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  • No doubt can be entertained that the greater part of the inner layer corresponds to the mesoderm of more ordinary embryos, for the coelomic pouches, the germ-cells, the musculature and the vascular system all arise from it.

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  • Two years later Nitzsch, who was indefatigable in his endeavour to discover the natural families of birds and had been pursuing a series of researches into their vascular system, published the result, at Halle in Saxony, in his Observationes de avium arteria carotide communi, in which is included a classification drawn up in accordance with the variation of structure which that important vessel presented in the several groups that he had opportunities of examining.

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  • Outside the wall of the oesophagus a vascular space has been detected which is in direct continuity with the longitudinal blood-vessels.

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  • In certain cases, however, the walls of the oesophagus appear to be very closely applied to the muscular body-wall and this vascular space thereby considerably reduced.

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  • 18, in the Heteronemertines the lateral stems, while entirely uniform all through the posterior portion of the body, no longer individually exist in the oesophageal region, but here dissolve themselves into a network of vascular spaces surrounding this portion of the digestive tract.

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  • The circulatory system of Carinella is considerably different, being more lacunar and less restricted to definite vascular channels.

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  • The vascular system is entirely closed.

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  • In origin the vascular system is due to a fusion of spaces which arise in the mesoblast of the larva.

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  • As a rule these organs only extend a short way along the anterior end of the body, a concentration which we may associate with the development of a vascular system I--- to bring the products of excretion to a fixed spot.

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  • There are no specialized sense-organs or vascular or respiratory systems. There is a wide body-cavity, but as this has no connexion with the renal or reproductive organs it cannot be regarded as a coelom, but probably is a blood-space or haemocoel.

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  • Specimens of flowering plants and vascular cryptograms are generally mounted on sheets of stout smooth paper, of uniform quality; the size adopted at Kew is 17 in.

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  • 4 About 310 species of vascular plants are found, of which about forty species are American, forty-four European-Asiatic, fifteen endemic, and the rest common both to America and Europe or Asia.

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  • It seems likely that the coelomic pore-canals were originally excretory organs, but in the existing Enteropneusta the pore-canals (especially the collar canals) have, as we have seen, acquired new functions or become vestigial, and the function of excretion is now mainly accomplished by a structure peculiar to the Enteropneusta called the glomerulus, a vascular complex placed on either side of the anterior portion of the stomochord, projecting into the proboscis-coelom.

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  • The vascular system itself is quite peculiar, consisting of lacunae and channels destitute of endothelium, situated within the thickness of the basementmembrane of the body-wall, of the gut-wall and of the mesenteries.

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  • The vascular system does not readily lend itself to morphological comparison between such widely different animals as Balanoglossus and Amphioxus, and the reader is therefore referred to the memoirs cited at the end of this article for further details.

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  • Correlated with the presence of the genital pleurae there is a pair of vascular folds of the basement membrane proceeding from the dorsal wall of the gut in the postbranchial portion of the branchio-genital region, and from the dorsal angles made by the pleural folds with the body-wall in the pharyngeal region; they pass, in their most fully developed condition, to the free border of the genital pleurae.

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  • These vascular membranes are called the lateral septa.

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  • On the inner surface of both valves several well-defined muscular, vascular and ovarian impressions are observable; they form either indentations of greater or less size and depth, or occur as variously shaped projections.

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  • 22) is hollow, and it contains a diverticulum "' s from the coelom, a branch of the vascular system, a nerve and some muscle fibres.

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  • This sinus is continued round the oesophagus as the peri-oesophageal sinus, and thus the whole complex of the small arm-sinus has the relations of the so-called vascular system of a Sipunculid.

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  • There is thus a vascular ring around the oesophagus.

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  • There is thus brought into play a series of processes on the part of the tissues - the vascular inflammatory changes - which is really the first move to neutralize the malign effects.

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  • The vascular changes are practically absent in healing by first intention.

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  • These vascular buds grow out in various directions as little solid projections of cells; they then become channelled and form the new but temporary meshwork.

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  • - Healing abscess showing a wall of young cellular and vascular granulation tissue, which separates the pus area (top of Fig.) from the muscle fibres seen at lower part of Fig.

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  • This reaction is carried out by the mobile phagocytes sometimes alone, sometimes with the aid of the vascular phagocytes, or of the nervous system."

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  • The discoveries of the separate paths of sensory and motor impulses in the spinal cord, and consequently of the laws of reflex action, by Charles Bell and Marshall Hall respectively, in their illumination of the phenomena of nervous function, may be compared with the discovery in the region of the vascular system of the circulation of the blood; for therein a key to large classes of normal and aberrant functions and a fertile principle of interpretation were obtained.

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  • Many other diseases formerly regarded as primarily diseases of the nervous system are not such; but, by means of agents either introduced into the body or modified there, establish themselves after the affinities of these in contiguous associated parts of the structure, as in vascular, membranous or connective elements, or again in distant and peripheral parts; the perturbations of nervous function being secondary and consequential.

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  • In heart disease the chief work of the latter half of the 19th century was, in the first quarter, such clinical work as that of William Stokes and Peter Mere Latham (1789-1875); and in the second quarter the fuller comprehension of the vascular system, central and peripheral, with its cycles and variations of blood pressure, venous and arterial.

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  • Vascular plants 154 1035 2743

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  • The vascular plants already described number about 1500 species.

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  • There is no trace of a true vascular system.

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  • There are no pores in the foot or elsewhere in Lamellibranchia by which water can pass into and out of the vascular system, as formerly asserted.

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  • ab, ac, ad, Three pit-like depressions in the median line of the foot supposed by some writers to be pores admitting water into the vascular system.

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  • i [3], [5]) are highly vascular flat processes richly supplied with nerves.

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  • The Molluscan ctenidium is typically a plume like structure, consisting of a vascular axis, on each side of which is set a row of numerous lamelliform or filamentous processes.

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  • Classification Of Lamellibranchia The classification originally based on the structure of the gills by P. Pelseneer included five orders, viz.: the Protobranchia in which the gill-filaments are flattened and not reflected; the Filibranchia in which the filaments are long and reflected, with non-vascular junctions; the Pseudo-lamellibranchia in which the gill-lamellae are vertically folded, the interfilamentar and interlamellar junctions being vascular or non-vascular; the Eulamellibranchia in which the interfilamentar and interlamellar junctions are vascular; and lastly the Septibranchia in which the gills are reduced to a horizontal paltition.

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  • Branchial filaments united by vascular interfilamentar junctions and vascular interlamellar junctions; the latter contain the afferent vessels.

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  • is formed, which is called the mesoderm, and gives rise to the muscular and connective tissues to the vascular system, and to the excretory and generative organs.

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  • (1875); " Note on the Coelom and Vascular System of Mollusca and Arthropoda," Quart.

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  • The stomach is formed upon much the same principle as that of the horse or rhinoceros, but is more elongated transversely and divided by a constriction into two cavities - a large left cul de sac, lined by a very dense white epithelium, and a right pyloric cavity, with a thick, soft, vascular lining.

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  • The typical foliage leaf consists of several layers, and amongst vascular plants is distinguishable into an outer layer (epidermis) and a central tissue (parenchyma) with fibro-vascular bundles distributed through it.

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  • In vascular acotyledonous plants there is frequently a tendency to fork exhibited by the fibro-vascular bundles in the leaf; and when this is the case we have f ork-veined leaves.

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  • The water taken up by the root from the soil contains nitrogenous and mineral salts which combine with the first product of photo-synthesis - a carbohydrate - to form more complicated nitrogen-containing food substances of a proteid nature; these are then distributed by other elements of the vascular bundles (the phloem) through the leaf to the stem and so throughout the plant to wherever growth or development is going on.

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  • When the vascular bundles reach the base of the lamina they separate and spread out in various ways, as already described under venation.

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  • In some Australian acacias, and in some species of Oxalis and Bupleurum, the petiole is flattened in a vertical direction, the vascular bundles separating immediately after quitting the stem and running nearly parallel from base to apex.

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  • The vascular bundles and cellular tissue are sometimes developed in such a way as to form a circle, with a hollow in the centre, and thus give rise to what are called fistular or hollow leaves, as in the onion, and to ascidia or pitchers.

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  • It resembles Dinophilus in the possession of a ventral pharyngeal pouch (which bears teeth in Histriodrilus only), the small number of segments, and absence of distinct septa, the absence of a vascular system, the presence of distinct ganglia on the ventral nerve cords, and of small nephridia which do not appear to open internally.

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  • g, Vascular spaces in tentacular cavity of the tentacular crown into vascular spaces.

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  • The vascular system has attained the highest state of development of all reptiles.

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  • The vascular bundles of the stem belong to the col xylem and the bast or phloem stand side by side on the same radius.

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  • Considering, however, that it is generally believed that Bryophyta and vascular plants are descended from an algal ancestry, it is natural to suppose that, prior to the luxuriant vegetable growths of the Carboniferous period, there must have existed an age of algae.

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  • 34, and in the constitution of its digestive, vascular, respiratory (branchial), excretory, skeletal, nervous and muscular systems it exhibits what appears to be a primordial condition of vertebrate organization, a condition which is, in fact, partly recapitulated in the course of the embryonic stages of craniate vertebrates.

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  • Thereafter the part becomes warm and painful, owing to marked local vascular dilatation.

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  • Gills or branchiae may be developed by parts of an appendage becoming thin-walled and vascular and either expanded into a thin lamella or ramified.

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  • In the Cirripedia, however, they are vascular processes from the inner surface of the mantle or shell-fold, and in some Ostracoda they are outgrowths from the sides of the body.

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  • Adaptations for aerial respiration are found in some of the landcrabs, where the lining membrane of the gill-chamber is beset with vascular papillae and acts as a lung.

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  • The vascular system is very rudimentary.

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  • There appears to be no vascular system.

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  • In internal structure grass-culms, save in being hollow, conform to that usual in monocotyledons; the vascular bundles run parallel in the internodes, but a horizontal interlacement occurs at the nodes.

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  • especially in relation to the origin of the vascular bundles which supply them, favours the view that the scutellum and pileole are highly differentiated parts of a single cotyledon,and this view is in accord with a comparative study of the seedling of grasses and of other monocotyledons.

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  • In structure a cycadean sporangium recalls those of certain ferns (Marattiaceae, Osmundaceae and Schizaeaceae), but in the development of the spores there are certain peculiarities not met with among the Vascular Cryptogams. With the exception of Cycas, the female flowers are also in the form of cones, bearing numerous carpellary scales.

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  • A thorough examination of cycadean seeds has recently been made by Miss Stopes, more particularly with a view to a comparison of their vascular supply with that in Palaeozoic gymnospermous seeds (Flora, 1904).

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  • In addition to these cauline (fi rstcell).(After strands (confined to the stem and not connected Webber.) with the leaves), collateral bundles are often met with in the pith, which form the vascular supply of terminal flowers borne at intervals on the apex of the stem.

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  • After the cambium has been active for some time producing secondary xylem and phloem, the latter consisting of sievetubes, phloem-parenchyma and frequently thick-walled fibres, a second cambium is developed in the pericycle; this produces a second vascular zone, which is in turn followed by a third cambium, and so on, until several hollow cylinders are developed.

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  • internally to some of the vascular lt, Leaf-traces in cortex.

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  • 9, c) some of which pursue a more or less vertical course, and by frequent anastomoses with one another form a loose reticulum of vascular strands; others are leaftraces on their way from the stele of the stem to the leaves.

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  • 9, pd), which increase in size to adapt themselves to the growth of the vascular zones.

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  • 9) one sees some vascular bundles following a horizontal or slightly oblique course in the cortex, stretching for a longer or shorter distance in a direction concentric with the woody cylinder.

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  • The vascular system of cycadean seedlings presents some features worthy of note; centripetal xylem occurs in the cotyledonary bundles associated with transfusion-tracheids.

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  • type of vascular structure, which Fossil (Eocene) leaf from the characterized the stems of many Island of Mull.

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  • The stalk of an ovule, considerably reduced in normal flowers and much larger in some abnormal flowers, is homologous with a leaf-stalk, with which it agrees in the structure and number of vascular bundles.

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  • Close to the apex of a shoot the vascular bundles of a leaf make their appearance as double strands, and the leaf-traces in the upper part of a shoot have the form of distinct bundles, which in the older part of the shoot form a continuous ring.

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  • A point of anatomical interest is the occurrence in the vascular bundles of the cotyledons, scale-leaves, and elsewhere of a few centripetally developed tracheids, which give to the xylem-strands a mesarch structure such as characterizes the foliar bundles of cycads.

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  • In Sciadopitys similar spurs occur, each bearing a single needle, which in its grooved surface and in the possession of a double vascular bundle bears traces of an origin from two needle-leaves.

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  • In 1869 van Tieghem laid stress on anatomical evidence as a key to the morphology of the cone-scales; he drew attention to the fact that the collateral vascular bundles of the seminiferous scale are inversely orientated as compared with those of the carpellary scale; in the latter the xylem of each bundle is next the upper surface, while in the seminiferous scale the phloem occupies that position.

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  • Eichler, one of the chief supporters of the simpler view, does not recognize in the inverse orientation of the vascular bundles an argument in support of the axillary-bud theory, but points out that the seminiferous scale, being an outgrowth from the surface of the carpellary scale, would, like outgrowths from an ordinary leaf, naturally have its bundles inversely orientated.

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  • The primary vascular bundles in a young conifer stem are collateral, and, like those of a Dicotyledon, they are arranged in a circle round a central pith and enclosed by a common endodermis.

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  • The vascular bundle entering the stern from a leaf with a single vein passes by a more or less direct course into the central cylinder of the stem, and does not assume the girdle-like form characteristic of the cycadean leaf-trace.

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  • The characters of leaves most useful for diagnostic purposes are the position of the stomata, the presence and arrangement of resin-canals, the structure of the mesophyll and vascular bundles.

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  • A pine needle grown iji continuous light differs from one grown under ordinary conditions in the absence of hypodermal fibres, in the absence of the characteristic infoldings of the mesophyll cell-walls, in the smaller size of the resin-canals, &c. The endodermis in Pinus, Picea and many other genera is usually a well-defined layer of cells enclosing the vascular bundles, and separated from them by a tissue consisting in part of ordinary parenchyma and to some extent of isodiametric tracheids; but this tissue, usually spoken of as the pericycle, is in direct continuity with other stem-tissues as well as the pericycle.

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  • It is of interest to note that the leaves of Gnetum, while typically Dicotyledonous in appearance, possess a Gymnospermous character in the continuous and plate-like medullary rays of their vascular bundles.

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  • Chirocrinus-alter, one of of the nervous, waterthe Rhomb i fera, showing the reduced vascular and blood-vas number and regular arrangement of the cular systems, testified thecal plates, and the concentration of to their Pelmatozoan ancestry.

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  • They are separated from fishes and batrachians (Pisces and Batrachians) on the one hand, and agree with reptiles, and birds (Reptilia and A y es) on the other, in the possession during intra-uterine life of the membranous vascular structures respectively known as the amnion and the allantois, and likewise in the absence at this or any other period of external gills.

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  • Root, stem and leaf can be distinguished even in the simplest forms, and the plant is traversed by a welldeveloped vascular system.

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  • The spores of the homosporous Vascular Cryptogams are usually of small size; the prothalli produced from them usually bear both antheridia and archegonia, though under special conditions an imperfect sexual differentiation may result.

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  • The systematic arrangement of the Vascular Cryptogams for the purposes of identification and description necessarily remains unchanged, while the comparative morpho logy is being more fully worked out.

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  • The vascular bundles equal in number the leaf-teeth from which they enter the stem and form a single ring.

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  • The vascular bundles themselves are collateral, the xylem consisting of the protoxylem, towards the centre of the stem, and two groups of xylem, between which the phloem is situated; the protoxylem elements soon break down, giving rise to the carinal canal.

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  • A, Longitudinal section of the rhizome, including a node and portions of the adjoining internodes; k, septum between the two internodal cavities, hh; gg, vascular bundles; 1, vallecular canal; s, leaf-sheath.

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  • B, Transverse section of the rhizome; g, vascular bundle; 1, vallecular canal.

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  • The single vascular bundle supplies a branch to the base of each sporangium.

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  • That these three sterile segments, with their sporangiophores, are together comparable to one of the bracts of Sphenophyllum, with its sporangiophores, is shown by the vascular supply in each case being derived from a single leaf-trace, So far as is at present known, the Sphenophyllales were homosporous.

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  • complanatum it is longer than in any other Vascular Cryptogam, and contains a number of canal cells.

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  • Thus the position of the root in Selaginella is different from what obtains in the other Vascular Cryptogams. A point of interest in this heterosporous genus is that the formation of the prothallus may commence before the megaspore is liberated from the sporangium.

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  • The spike is most simple in Ophioglossum, where it bears on each side a row of large sporangia, which hardly project from the surface, the vascular bundles occupying a central position.

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  • The stem is monostelic, the vascular tissues being separated into curved groups comparable with collateral vascular bundles, which surround the pith.

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  • It has thus led to a condition of uncertainty as regards the relationship of the great groups of Vascular Cryptogams, in which, however, lies the hope of an ultimate approach to a satisfactory solution.

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  • If, as has been suggested by Bower, the strobiloid types are relatively primitive, the large-leaved Pteridophyta must be supposed to have arisenearly from such forms. The question cannot be discussed fully here, but enough has been said above to show that in the light of our present knowledge the main phyla of the Vascular Cryptogams cannot be placed in any serial relationship to one another.

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  • The most important positive evidence on this point indicates that the most ancient Gymnosperms were derived from the Filicales rather than from any other phylum of the Vascular Cryptogams. Extinct forms are known intermediate between the Ferns and the Cycads, and a number of these have been shown to bear seeds and must be classed as Pteridospermae.

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  • The vascular system contains numerous red bloodcorpuscles.

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  • The praeseptal cavity is a vascular space, since it is in free communication with the dorsal vessel of the larva, and it persists in part as the two lophophoral vascular crescents of the adult.

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  • Even if it be admitted that the postseptal space may be the metasomatic cavity, the praeseptal space can hardly be regarded as coelomic in nature, since it is in continuity with the vascular system; while Masterman's conclusion that the cavity of the praeoral hood (the supposed proboscis-cavity) is separated from that of the supposed collar has received no confirmation.

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  • At present 435 species of phanerogams and vascular cryptogams are known; the lower orders have been little investigated.

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  • According to the Prodromus florae hispanicae of Willkomm and Lange (completed in 1880), the number of species of vascular plants then ascertained to exist in the country was 5096.

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  • These structures are all enclosed in the middle subcorneous integument, a continuation of the ordinary skin of the limb, but extremely vascular, and having its superficial extent greatly increased by being developed into papillae or laminae.

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  • It is formed of pavement epithelial cells, mainly grouped in a concentric manner around the vascular papillae of the subcorneous integument, so that a section near the base of the hoof, cut transversely to the long axis of these papillae, shows a number of small circular or oval orifices, with cells arranged concentrically round them.

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  • Between the mucous membrane and the bone of the hard palate is a dense vascular and nervous plexus.

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  • contains blood, and forms part of the vascular system.

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  • Peripatus is an Arthropod, as shown by (1) the presence of appendages modified as jaws; (2) the presence of paired lateral ostia perforating the wall of heart and putting its cavity in communication with the pericardium; (3) the presence of a vascular body cavity and pericardium (haemocoelic body cavity); (4) absence of a Derivisceral section of the coelom.

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  • the central nervous system, and the main vascular trunk or heart, they may be considered as indicating affinities in that direction.

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  • Body cavity is continuous with the vascular system, and does not communicate with the paired nephridia.

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  • A, Eafly stage; no trace of the vascular space; endoderm and ectoderm in contact.

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  • The vascular bundles sometimes form a prominent rib, which indicates the middle of the sepal; at other times they form several ribs.

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  • It has recently been stated, however, that the supposed Algae are in reality the megaspores of Vascular Cryptogams. Scarcely anything is known of Palaeozoic Florideae; Solenopora, ranging from the Ordovician to the Jurassic, resembles, in the structure of its thallus, with definite zones of growth, Corallinaceae such as Lithothamnion, and may probably be of the same nature.

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  • Our knowledge of the Vascular Cryptograms of the Palaeozoic period, though recent discoveries have somewhat reduced their relative importance, is still more extensive than of any.

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  • We must bear in mind that throughout the Palaeozoic period, and indeed far beyond it, vascular plants, so far as the existing evidence shows, were represented only by the Pteridophyta, Pteridosperms and Gymnosperms. Although the history of the Angiosperms may probably go much further back than present records show, there is no reason to suppose that they were present, as such, amongst the Palaeozoic vegetation.

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  • Hence it is not surprising to find that the early Vascular Cryptograms were, beyond comparison, more varied and more highly organized than their displaced and often degraded successors.

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  • Part of transverse section of a young stem, showing pith, vascular bundles with secondary wood, and cortex.

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  • (x 6z.) B, Stamens more highly magnified: g, vascular bundle of filament; e, pollen-sac after dehiscence.

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  • The longitudinal course of the vascular bundles and their relation to the leaves in Calamarieae generally followed the Equisetum type, though more variable and sometimes more complex.

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  • Where the structure of the leaves is preserved it proves to be of an extremely simple type; the narrow lamina is traversed by a single vascular bundle, separated by a sheath from the surrounding palisadeparenchyma.

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  • The Palaeozoic Calamarieae, though so far surpassing recent Equisetaceae, both in stature and complexity of organization, clearly belonged to the same class of Vascular Cryptogams. There is no satisfactory evidence for attributing Phanerogamic e bn FIG.

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  • Each sporangiophore is traversed throughout its length by a vascular bundle connected with that which supplies the subtending bract.

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  • The diarch roots of a Sphenophyllum have been described by Renault, who has also investigated the leaves; they were strongly constructed mechanically, and traversed by slender vascular bundles branching dichotomously.

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  • Vascular bundles.

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  • The axis of the cone in Cheirostrobus contains a polyarch stele, with solid wood, from the angles of which vascular bundles pass out, dividing in the cortex, to supply the various segments of the sporophylls.

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  • On the scar are three prints, the central one alone representing the vascular bundle, while the lateral prints (parichnos) mark the position of merely parenchymatous strands.

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  • v.b., Print of vascular bundle.

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  • The latter shows marked xerophytic adaptations; the single vascular bundle was surrounded by a sheath of short tracheides, and the stomata were sheltered in two deep furrows of the lower surface.

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  • group in habit, for they appear to have vb, Vascular bundle.

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  • vb, Its vascular bundle.

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  • vb, Vascular bundle.

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  • All these names, vb, Print of vascular bundle.

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  • mamillaris) there is evidence that they were of the Sigillariopsis type, the leaf being traversed by two parallel vascular strands, derived from the bifurcation of the leaf-trace.

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  • - Of all Vascular Cryptogams the Ferns have best maintained their position down to the present day.

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  • The petiole was usually traversed by a single vascular bundle, hippocrepiform in section - a marked point of difference from the more complex petioles of recent Marattiaceae.

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  • a, Vascular bundle; c, hairs; b, d, annulus, magnified.

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  • The genus Zygopteris, of which numerous Carboniferous and Permian species are known, likewise had a monostelic stem, but the structure of its vascular cylinder was somewhat complex, resembling that of the most highly differentiated Hymenophyllaceae, with which some species of Zygopteris also agreed in the presence of axillary shoots.

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  • The single vascular bundle which traversed the petiole and its branches was concentric, the leaves resembling those of Ferns in structure as well as in habit.

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  • The seed was stalked, and there is an exact agreement in structure between the vascular strands of the stalk and cupule of the seed, and those of the rachis and leaflets of Lyginodendron, thus confirming the evidence from the glands.

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  • The single integument is united to the nucellus, except at the top, and is traversed by about nine vascular strands.

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  • vb, Vascular bundles of stalk, cupule and integument.

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  • Scott, having its own vascular system.

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  • This genus, from the Permo-Carboniferous of Autun, is represented by large, fleshy, reniform leaves or leaflets, with radiating dichotomous venation; the vascular bundles have in all respects the structure of those in the leaves of Cycads or Cordaiteae.

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  • The Upper Carboniferous and Permian plants may be grouped together as constituting a Permo-Carboniferous flora characterized by an abundance of arborescent Vascular Cryptogams and of an extinct class of plants to which the name Pteridosperms has recently been assigned - plants exhibiting a combination of Cycadean and filicinean characters and distinguished by the production of true gymnospermous seeds of a complex type.

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  • The Palaeozoic types are barely represented; the arborescent Vascular Cryptogams have been replaced by Cycads, Ginkgoales and Conifers as the dominant classes, while Ferns continue to hold their own.

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  • 15, 4 and 7), as investigated in English, French, Italian, and American specimens, may be briefly described as a short lateral shoot or peduncle, arising in a leaf-axil and terminating in a bluntly rounded apex, bearing numerous linear bracts enclosing a central group of appendages, some of which consist of slender pedicels traversed by a vascular strand and bearing a single terminal ovule enclosed in an integument, which forms a distal canal or micropyle.

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  • i, Bennettites stem: portion of transverse section of stem; a, vascular cylinder; b, leaf-traces; c, pith; d, cortex.

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  • 3, Bennettites stem, leaf-traces attached to the vascular cylinder and passing as simple strands through the cortex; d, cortex.

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  • Starting with the Permo-Carboniferous vegetation, and omitting for the moment the Glossopteris flora, we find a comparatively homogeneous flora of wide geographical range, consisting to a large extent of arborescent lycopods, calamites, and other vascular cryptogams, plants which occupied a place comparable with that of Gymnosperms and Angiosperms in our modern forests; with these were other types of the greatest phylogenetic importance, which serve as finger-posts pointing to lines of evolution of which we have but the faintest signs among existing plants.

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  • Vascular Cryptogams still include one or two large horsetails with stems over an inch thick, and also 37 species of Fern, amongst the most interesting of which are 5 species belonging to the climbing Lygodium, a genus now living in Java.

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  • We have developed a mouse model of vascular injury and, using our published technique, can measure leukocyte adhesion to artery segments.

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  • Both vascular and airway smooth muscles relax in response to beta adrenergic agonists via cyclic AMP.

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  • The management of lower limb amputees was being provided within a busy, acute vascular unit.

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  • Award powers research into prosthesis success Most older vascular amputees fail to cope with their prostheses.

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  • anastomosis in vitro experiments are performed on artificial and natural heart valves, vascular anastomoses and within the chambers of the heart.

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  • angiography for carotid artery stenosis and peripheral vascular disease: a systematic review.

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  • arteriosclerosis thrombosis and Vascular Biology; Hypertension; and Stroke.

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  • artery stenosis or peripheral vascular disease.

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  • Abstract Fossil evidence of terrestrial vascular plant life and terrestrial arthropods exists from the Silurian.

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  • Back to List Birth Marks More than 10 in 100 babies have vascular birthmarks.

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  • In the second hour there's great old time gospel bluegrass and cardio vascular exercise.

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  • In the second hour we've got bluegrass gospel, cardio vascular exercise and great old time bluegrass music.

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  • This enzyme catalyzes the conversion of angiotensin I to angiotensin II in blood plasma and in vascular endothelial tissues and degrades bradykinin.

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  • The dark spots on the scar, mark where the vascular bundles which carried the sap passed through from the twig into the leaf.

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  • She is currently based at Great Ormond Street Hospital where she is doing an MD on vascular calcification in children with end-stage renal disease.

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  • carotid artery stenosis or peripheral vascular disease.

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  • For a vascular assessment it is necessary to establish whether the patient has intermittent claudication.

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  • During the third month, these break up forming cell nests surrounded by young vascular connective tissue.

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  • Treatment Successful surgery will usually prevent the continuance of pulmonary hypertension, and the development of Pulmonary Vascular Disease.

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  • Care with ACE inhibitors is required in the presence of peripheral vascular disease or raised serum creatinine.

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  • The potent angiogenic cytokine vascular endothelial growth factor (VEGF) appears to play a role in this process (Ref.

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  • Aspirin may also help to reduce the risk of strokes, which may cause vascular dementia.

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  • A vacancy exists for a vascular nurse specialist to work within the general surgical directorate.

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  • Internal, vascular discoloration in affected plants extended from the base of the stem upward.

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  • duplex ultrasound has been increasingly used in vascular assessments.

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  • Recent studies have shown that passive smoking may be associated with vascular endothelial dysfunction.

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  • Auxins control a number of developmental processes in plants, including cell elongation, the formation of vascular tissue and meristem organization.

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  • There are also close links with the vascular surgeons to ensure delays in patients needing carotid endarterectomy are kept to a minimum.

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  • Kidney disease To study the regulation of complement activity on vascular endothelium; implications for kidney disease.

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  • Vascular integrity in the healthy endothelium is maintained through the release of a variety of paracrine factors such as nitric oxide (NO ).

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  • A conical vascular body forming the extremity of the penis.

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  • fibroid embolization for symptomatic leiomyomata Journal of Vascular and Interventional Radiology.

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  • The lichen and bryophyte flora of the complex is outstanding, and the vascular plant flora is also extremely rich.

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  • genesis of vascular disease Annu.

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  • Notable examples are hip joints, and replacement heart valves and vascular grafts.

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  • Endothelin-1 and aldosterone play a critical role in vascular homeostasis and their high levels have been implicated in high altitude disorders.

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  • inadvertent injection of drugs into the arterial circulation may result in vascular spasm with loss of tissue due to anoxia.

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  • The major killers today are heart and vascular disease, chronic degenerative diseases and cancer, largely incurable and increasing in incidence.

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  • Expect that team, as a minimum, to: Investigate and treat vascular insufficiency.

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  • There is a need for more research into the treatment of vascular malformations.

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  • native vascular plant species, many of which are the subject of conservation concern.

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  • nitric oxide synthase: role in the genesis of vascular disease Annu.

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  • The project has been funded to investigate the causes of cardio vascular problems and cancer using numerical modeling.

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  • The vascular unit offers experience in care of the high dependency patient, surgical nursing, rehabilitation and palliative care of the patient.

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  • Blood pressure in both arms - unequal blood pressures suggests proximal vascular occlusion.

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  • Collaborative overview of randomized trials of antiplatelet therapy II: Maintenance of vascular graft or arterial patency by antiplatelet therapy.

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  • Molecular basis of the coronary vascular actions of natriuretic peptides.

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  • These molecules induce smooth muscle contraction and enhance vascular permeability.

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  • Predisposition to motor neuron degeneration because of the glial, vascular, and lymphatic changes caused by poliovirus.

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  • A sound knowledge of the role of interventional radiology in the management of vascular disease.

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  • A fourth Fellow in vascular interventional radiology will be appointed soon ).

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  • ROP is an alteration to this development Distinct demarcation line between vascular and avascular retina develops into a ridge.

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  • revolutionized the treatment of vascular disease.

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  • The vascular plant component is always poor, but richer communities support opposite-leaved golden saxifrage and mossy saxifrage.

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  • Sample groups People with carotid artery stenosis or peripheral vascular disease.

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  • John Scurr, senior consultant vascular surgeon who organized the meeting attended by airline doctors said?

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  • suture held by the first assistant using vascular dissecting forceps.

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  • Improving blood flow to the peripheral limbs with a surgical vascular graft or a chemical sympathectomy.

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  • Higher plant taxonomy Scotland has 1,000 native vascular plant species, many of which are the subject of conservation concern.

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  • With recent technological advances, duplex ultrasound has been increasingly used in vascular assessments.

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  • unimproved grasslands on neutral or acidic soils are likely to contain at least 12 species of vascular plant per meter square.

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  • vascular malformations cause no symptoms at all.

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  • vascular endothelium; implications for kidney disease.

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  • vascular dementia.

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  • vascular permeability.

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  • vascular Technologists working in Great Britain and Ireland.

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  • vascular surgeon Duncan Black said: " We had to open up his chest to give him a heart massage.

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  • Muscle Dull red in color, highly vascular and tears easily.

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  • Rapid absorption, such as from a very vascular site ie mucous membranes.

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  • If this process can be halted, the tumor will stop growing an approach called vascular targeting.

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  • Phloem The plant tissue that transports soluble food and minerals around a plant body (if the plant has vascular tissue ).

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  • It acts as a peripheral vasodilator and has beneficial effects on collagen, a vital structural component of the vascular system.

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  • vein resection was performed in 15 patients, only two underwent major hepatectomy and none had vascular reconstruction.

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  • It appears probable that there is a vascular connexion be- ` tween these and the male `/ / individuals, which thus derive their nutriment from the neuters.

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  • The viscid pulp soon hardens, affording a protection to the seed; in germination the sucker-root penetrates the bark, and a connexion is established with the vascular tissue of the first plant.

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  • HORSETAIL (Equisetum), the sole genus of the botanical natural order Equisetaceae, consisting of a group of vascular cryptogamous plants (see Pteridophyta) remarkable for the vegetative structure which resembles in general appearance the genera of flowering plants Casuarina and Ephedra.

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  • This observation led him to further work, and he succeeded in showing that in vascular organs the presence of cells in inflammatory exudates is not the result of exudation but of multiplication of pre-existing cells.

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  • The vast majority of the mammalia are provided with an organ in the uterus, by which, before the birth of their young, a vascular connexion is maintained between the embryo and the parent animal.

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  • The Ferns and fern-like plants (see PTERIDOP1IYTA) have on the other hand a well developed independent sporophyte which is differentiated into stem, leaf and root with highly organized internal structure including true vascular bundles.

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  • In general structure they approach the Phanerogams with which they form collectively the Vascular Plants as contrasted with the Cellular PlantsThallophyta and Bryophyta.

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  • The sporophyte is the plant which is differentiated into stem, leaf and root, which show a wonderful variety 01 form; the internal structure also shows increased complexity and variety as compared with the other group of vascular plants, the Pteridophyta.

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  • In many forms its hyphae are particularly thick-walled, and may strikingly resemble the epidermis of a vascular plant.

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  • (In one genus (Lactarius) milk-tubes, recalling the laticiferous tubes of many vascular plants, are found.) These elongated hyphae are frequently thick-walled, and in some cases form a central strand, which may serve to resist longitudinal pulling strains.

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  • But these two principles do not find their full expression till we come, in the ascending series, to the Vascular Plants.

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  • A richly chlorophyllous tissue, with numerous intercellular spaces communicates with the exterior by stomata, strikingly similar to those of the vascular plants (see below).

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  • Outside this are three arcs of large cells showing characters typical of the endodermis in a vascular plan.t; these are interrupted by strands ofnarrow, elongated, thick-walled cells, which send branches into the little brown scales borne by the rhizome.

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  • The surface layer of the rhizome bears rhizoids, and its whole structure strikingly resembles that of the typical root of a vascular plant.

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  • Vascular Plants.In the Vascular Plants (Pteridophytes, i.e.

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  • The body of the sporophyte in the great majority of the vascular plants shows a considerable increase in complexity over that found in the gametophyte of Bryophytes.

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  • The root differs from the shoot in the characters of its surface tissues, in the absence of the green assimilative pigment chlorophyll, in the arrangement of its vascular system and in the mode of growth at the apex, all features which are in direct relation to its normally subterranean life and its fixative and absorptive functions.

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  • In the Vascular Plants this tissue is collectively known as the vascular system.

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  • One of the most striking characters common to the two highest groups of plants, the Pteridophytes and Phanerogams, is the Vascular possession of a double (hydrom-leptom) conducting .s system, such as we saw among the highest mosses, YS em.

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  • It is confined to the sporophyte, which forms the, leafy plant in these groups, and is known as the vascular system.

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  • The stelar system of Vascular Plants has no direct phylogenetic connection with that of the mosses.

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  • c eun~7 Such an arrangement of vascular tissue is called radial, ~

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  • Such a vascular cylinder is called a haplostele, and the axis containing it is said to be haplostelic. In the stele of the root the strands of tracheids along the lines where the xylem touches the pericycle are spiral or annular, and are the xylem elements first formed when the cylinder is developing.

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  • ft1.Types of Stole in Vascular Plants.

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  • The type of siphonostele characteristic of many ferns, in which are found internal phloem, and an internal endodermis separating the vascular conjunctive from the pith is known as a solenostele.

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  • For this reason a stem in which as pot ystelic, the term stele being transferr~d from the primary I central cylinder of the i~xis and applied to the vascular strands just described.

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  • The splitting up of the vascular tube I into separate strands does not depend wholly upon the occurrence I of leaf-gaps.

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  • In some forms other gaps (perforations) appear in the vascular tube placing the pith and cortex in communication.

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  • In other cases the leaf-gaps are very broad and long, the meristeles separating them being reduced to comparatively slender strands, while there is present in each gap a network of fine vascular threads, some of which run out to the leaf, while others form cross-connections between these leaf-trace strands and also with the main cauline meristeles.

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  • In some solenostelic ferns, and in many dictyostelic ones additional vascular strands are present which do not form part of the primary vascular tube.

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  • Sometimes a complete internal vascular cylinder, having the same structure as the primary one, and concentric with it, occurs in the pith, and others may appear, internal to the first (Matonia, Saccoloma).

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  • In such cases the vascular system is said to be polycyclic in contrast with the ordinary monocyclic condition, These internal strands or cylinders are to be regarded as peculiar types of elaboration of the stele, and probably act as reservoirs for water-storage which can be drawn upon when the water supply from the root is deficient.

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  • The vascular supply of the leaf (leaf-trace) consists of a single strand only in the haplostelic and some of the more primitive siphonostelic forms. In the microphyllous groups Leaf.trace of Pteridophytes (Lycopodiales and Equisetales) in and Petlolar which the leaves are small relatively to the stem, the Strands, single bundle destined for each leaf is a small strand whose departure causes no disturbance in the cauline stele.

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  • In the megaphyllous forms, on the other hand, (Ferns) whose leaves are large relatively to the stem, the departure of the correspondingly large trace causes a gap (leaf-gap) in the vascular cylinder, as already described.

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  • The evolution of the vascular structure of the petiole in the higher ferns is strikingly parallel with that of the stem, except in some few special cases.

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  • There is good reason to believe that the haplostele is primitive in the evolution of the vascular system.

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  • Polycycly was derived independently from monocycly in solenostelic and in dictyostelic forms. In the formation of the stem of any fern characterized in the adult condition by one of the more advanced types of vascular structure all stages of increase in complexity from the haplostele of the first-formed stem to the particular condition characteristic of the adult stem are gradually passed through by a series of changes exactly parallel with those which we are led to suppose, from the evidence obtained by a comparison of the adult forms, must have taken place in the evolution of the race, There is no more striking case in the plantkingdom of the parallel between ontogeny (development of the individual) and phylogeny (development of the race) so well known in many groups of animals.

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  • The leaves of the more primitive members of this series were entirely fern-like and possessed a fern-like vascular strand; while in the later members, including the modern Cycads, the leaf bundles, remaining unaffected by secondary thickening, are mesarch, while those of the stem-stele have become endarch.

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  • Among the existing Cycads, though the type of vascular system conforms on the whole with that of the other existing seed-plants, peculiar structures are often found (e.g.

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  • The typical structure of the vascular cylinder of the adult primary stem in the Gyrnnosperms and Dicotyledons is, like that of the higher ferns, a hollow cylinder of vas- Structure of cular tissue enclosing a central parenchymatous pith.

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  • The vascular tissue is typically separable into distinct collateral bundles (figs.

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  • Purely cauline vascular strands (i.e.

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  • In the blade of a typical leaf of a vascular plantessentially a thin plate of assimilating tissuethe vascular system takes the form of a number of separate, usually branching and anastomosing strands.

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  • i&Vertical section of a Palm-stem showing the root as it is found in most Pteridophytes vascular bundle,, Jr. curving and many Phanerogams has been already inwards and then outwards.

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  • The radial structure is characteristic of all root-steles, which have in essential points a remarkably uniform structure throughout the vascular plants, a fact no doubt largely dependent on the very uniform conditions under which they live.

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  • The body of a vascular plant is developed in the first place by repeated division of the fertilized egg and the growth of Develop- the products of division.

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  • Later, the axis branches by the formation of new growing-points, and in this way the complex system of axes forming the body of the ordinary vascular plant is built up. In the flowering plants the embryo, after developing up to a certain point, stopf growing and rests, enclosed within the seed.

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  • In many Pteridophytes thi first leaf is formed very early, and the first vascular strand i!

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  • In this case also the differentiation of leaf-bundles, which typically begins at the base of the leaf and extends upwards into the leaf and downwards into the stem, is the first phenomenon in the development of vascular tissue, and is seen at a higher level than the formation of a stele.

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  • Where a large-celled pith is developed this often becomes obvious very early, and in some cases it appears to have separate initials situated below those of the hollow vascular cylinder.

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  • The differentiation of the stelar stereom, which usually takes the form of a sclerized pericycle, and may extend to the endocycle and parts of the rays, takes place in most cases later than the formation of the primary vascular strand.

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  • The periblem, one cell thick at the apex, produces the cortex, to which the piliferous layer belongs in Monocotyledons; and the plerome, which is nearly always sharply separated from the periblem, gives rise to the vascular cylinder.

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  • Thi vascular system is connected in various ways with that of th(parent axis by the differentiation of bundle-connections across thi cortex of the latter.

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  • Every great group or phylum of vascular plants, when it has become dominant in the vegetation of the world, has produced members with the tree habit arising by the formation of a thick woody trunk, in most cases by the activity of a cambium.

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  • It is essentially a living tissue, and serves to place all the living cells of the secondary vascular tissues in communication.

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  • The tissue-elements just described are found only in the more complicated secondary vascular tissues of certain Dicotyledons.

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  • A considerable evolution in complexity can be traced in passing from the simplest forms of xylem and phloem found in the primary vascular tissues both among Pteridophytes and Phanerogams to these highly differentiated types.

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  • The, primary vascular tissues of Angiosperms are likewise nearly always simple, consisting merely of tracheae and sieve-tubes often associated with amylom.

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  • The main feature is the development of special vascular stereom and storage tissue.

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  • In some cases special secreting tissues, resin ducts, oil glands, laticiferous tissue, crystal sacs, &c., may be developed among the ordinary secondary vascular elements.

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  • When the vascular tissue of such plants is arranged Camblum in separate bundles these are said to be closed.

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  • Sometimes the original cambial ring is broken into several arcs, each of which is completed into an independent circle, so that several independent secondary vascular cylinders are formed.

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  • Opposite the primary xylems, the cambium either (a) forms parenchyma on both sides, making a broad, secondary (principal) ray, which interrupts the vascular ring and is divided at its inner extremity by the islet of primary xylem; or (b) forms secondary xylem and phloem in the ordinary way, completing the vascular ring.

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  • Thus the structure of an old thickened root approximates to that of an old thickened stem, and so far as the vascular tissue is concerned can often only be distinguished from the latter by the position and orientation of the primary xylems. The cambium of the primary root, together with the tissues which it forms, is always directly continuous with that of the primary stem, just in the same way as the tissues of the primary stele.

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  • In nearly all plants which produce secondary vascular tissues by means of a cambium there is another layer of secondary meristem arising externally to, but in quite the same fashion as, Ph II

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  • The phellogen may arise, in the first place, in any tissue of the axis external to the actual vascular tissuesi.e.

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  • supplementary vascular bundles, anomalous cambial zones, &c. It is often enormously developed and forms a very important tissue in roots.

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  • The new work largely centred round a discussion of the nature and origin of vessels, conspicuous features in young plant tissues which thus acquired an importance in the contemporary literature out of proportion to their real significance in the construction of the vascular plant.

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  • of our knowledge of the structure and course of the vascular strands of the higher plants (IJeber den Bau und die Anordnung der Gefssbundel bei den Stamm und Wurzel der Phanerogamen, Beitrage zur wissenschaftlichen Botanik, Heft i., Leipzig, 1859); to the second the establishment of the sound morphological doctrine of the central cylinder of the axis as the starting-point for the consideration of the general arrangement of the tissues, and the first clear distinction between primary and secondary tissues (Botanische Zeitung, 186I and 1863); to the last the putting together of the facts of plant anatomy known up to the middle of the eighth decade of the century in that great encyclopaedia of plant anatomy, the Vergleichende Anatomie der Vegetationsor gene bei den Phanerogamen und Farnen (Stuttgart, 1876; Eng.

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  • While convincing us that the plants of past ages in the earths history were exposed to very similar conditions of life, and made very much the same adaptive responses as their modern representatives, one of the main results of this line of work has been to reveal important data enabling us to fill various gaps in our morphological knowledge and to obtain a more complete picture of the evolution of tissues in the vascular plants.

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  • Since about 1895 this branch has been most actively pursued in England, where the work of Boodle and of Gwynne-Vaughan especially on Ferns) has been the most important, leading to a coherent theory of the evolution of the vascular system in these plants (Tansley, Evolution of the Filicinean Vascular System, Cambridge, 1908); and in America, where Jeffrey has published important papers on the morphology of the vascular tissues of the various groups of Pteridophytes and Phanerogams and has sought to express his conclusions in a general morphological theory with appropriate terminology.

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  • The increasing development of the wood as the tree grows older is largely due to the demands for the conduction of water and mineral matters dissolved in it, which are made by the increased number of leaves which from year to year it bears, and which must each be put into communication with the central mass by the formation of new vascular bundles.

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  • The importance of this provision in the case of aquatic vascular plants of sturdy bulk is even greater than in that of terrestrial organisms, as their environment offers considerable obstacles to the renewal of the air in their interior.

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  • The older is that the water travels in the woody cell-walls of the vascular bundles, mainly under the action of the forces of root pressure and transpiration, and that the cavities of the vessels contain only air.

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  • After making its way into the interior, the intruder sets up a considerable hyper trophy of the tissue, causing the formation of a tubercle, which soon shows a certain differentiation, branches of the vascular bundles of the root being supplied to it.

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  • They are supplied with a regular system of conducting vascular bundles communicating with those of the roots.

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  • In the vascular cryptogams and phanerogams it takes place in the spore mother cells and the reduced number is found in all the cells of the gametophyte, the full number in those of the sporophyte.

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  • In Monoblepliaris, one of the lower Fungi, in some Algae, in the Vascular Cryptograms, in Cycads (Zamia and Cycas), and in Ginkgo, an isolated genus of Gymnosperms, the male cell is a motile spermatozoid with two or more cilia.

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  • In the Characeae, the Vascular Cryptogams, in Zamia and Cycas, and in Ginkgo, the spermatozoids are more or less highly modified cells witi+m.-S, ~..

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  • At the an ~ ~ tenor end are attached - two cilia or flagella In, , C the Vascular Cryptogams -- ~ the structure is much the;il ~.: -; same, but a more or less ~ ~ ~ spherical mass of cyto 4 i~- - ~ plasm remains attached .8 ~ :~ to the posterior spirals, -.

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  • In the spermatozoids of Chara, Vascular Cryptogams, and in those of Cycas, Zamia and Ginkgo, the cilia arise from a centrosome-like body which is found on one side of the nucleus of the spermatozoid mother-cell.

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  • It was characterized by arborescent vascular Cryptogams and Gymnosperms of a type (Cordaiteae) which have left no descendants beyond it.

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  • Both were in turn replaced by the Lower Mesozoic flora, which again is thought to have had its birth in the hypothetical Gondwana land, and in which Gymnosperms played the leading part formerly taken by vascular Cryptogams. The abundance of Cycadean plants is one of its most striking features.

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  • Internally they are found to consist of a lamina twisted upon itself, and externally they generally exhibit a tortuous structure, produced, before the cloaca was reached, by the spiral valve of a compressed small intestine (as in skates, sharks and dog-fishes); the surface shows also vascular impressions and corrugations due to the same cause.

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  • From near the entrance of the optic nerve, through the original choroidal fissure, arises the much-folded pecten, deeply pigmented and very vascular, far into the vitreous humour.

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  • Vascular System.

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  • The arrangement of the conducting tissue in the stem is characteristic; a transverse section of the very young stem shows a nunber of distinct conducting strands - vascular bundles - arranged in a ring round the pith; these soon become united to form a closed ring of bast and wood, separated by a layer of formative tissue (cambium).

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  • Thus in the Chaetopoda the perivisceral cavity is coelomic; in this respect the group contrasts with the Arthropoda and Molluscs, where the perivisceral cavity is, mainly at least, part of the vascular or haemal system, and agrees with the Vertebrata.

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  • This is the vascular or haemal system (formerly and unnecessarily termed pseudhaemal).

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  • With a few exceptions among the Polychaeta the vascular system is always present among the Chaetopoda, and always consists of a system of vessels with definite walls, which rarely communicate with the coelom.

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  • The main trunks of the vascular system often possess valves at the origin of branches which regulate the direction of the blood flow.

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  • The vascular system is in the majority of Chaetopods a closed system.

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  • Goodrich), that among the Hirudinea the coelom, which is largely broken up into narrow tubes, may be confluent with the tubes of the vascular system.

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  • the Capitellidae, in which the vascular system has vanished altogether, leaving a coelom containing haemoglobin-impregnated corpuscles.

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  • In the case of many Oligochaeta where there is no vascular network surrounding the nephridium, this function must be the chief one of those glands, the more elaborate process of excretion taking place in the case of nephridia surrounded by a rich plexus of blood capillaries.

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  • Vascular system generally present forming a closed system of tubes.

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  • Vascular and 8, 8 and 9, the oviducal pores system always present, upon the 14th and the male pores forming a closed system, upon the 18th segment.

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  • The vascular system is simple with as a rule direct communication between dorsal and ventral vessels in each segment.

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  • Sperm ducts and atria as in Limicolae; egg sacs large; body wall thick; vascular system and nephridia as in Terricolae.

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  • Vascular system complicated without regular connexion between dorsal and ventral vessels, except in anterior segments.

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  • Nephridia as a rule with abundant vascular supply.

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  • The vascular system is as in the lower Oligochaeta.

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  • Coelom generally reduced to a system of tubes, sometimes communicating with vascular system; in Acanthobdella and Ozobranchus a series of metamerically arranged chambers as in Oligochaeta.

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  • Neither in this genus nor in the last is there any communication between coelom and vascular system.

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  • Goodrich that the vascular system and the coelom are in communication (as in vertebrates by means of the lymph system).

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  • On the other hand, it has been held that in these leeches there is no vascular system at all and that the entire system of spaces is coelom.

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  • In favour of regarding the vascular system as totally absent, is the fact that the median coelomic channels contain no dorsal and ventral vessel.

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  • In favour of seeing in the lateral trunks and their branches a vascular system, is the contractility of the former, and the fact of the intrusion of the latter into the epidermis, matched among the Oligochaeta, where undoubted blood capillaries perforate the epidermis.

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  • The vascular system is not extensive, the arteries soon ending in the well-marked spongy tissue which builds up the muscular foot, parapodia, and dorsal body-wall.

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  • The body-cavity and the muscular, fibrous and vascular tissues are traced partly to two symmetrically disposed " mesoblasts," which bud off from the invaginated arch-enteron, partly to cells derived from the ectoderm, which at a very early stage is connected by long processes with the invaginated endoderm.

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  • No doubt can be entertained that the greater part of the inner layer corresponds to the mesoderm of more ordinary embryos, for the coelomic pouches, the germ-cells, the musculature and the vascular system all arise from it.

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  • Two years later Nitzsch, who was indefatigable in his endeavour to discover the natural families of birds and had been pursuing a series of researches into their vascular system, published the result, at Halle in Saxony, in his Observationes de avium arteria carotide communi, in which is included a classification drawn up in accordance with the variation of structure which that important vessel presented in the several groups that he had opportunities of examining.

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  • seems to have attempted to found any scientific arrangement of birds on other than external characters until, in 1837, William Macgillivray issued the first volume of his History of British Birds, wherein, though professing (p. 19) " not to add a new system to the many already in partial use, or that have passed away like their authors," he propounded (pp. 16-18) a scheme for classifying the birds of Europe at least founded on a " consideration of the digestive organs, which merit special attention, on account, not so much of their great importance in the economy of birds, as the nervous, vascular and other systems are not behind them in this respect; but because, exhibiting great diversity of form and structure, in accordance with the nature of the food, they are more obviously qualified to afford a basis for the classification of the numerous species of birds " (p. 52).

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  • Outside the wall of the oesophagus a vascular space has been detected which is in direct continuity with the longitudinal blood-vessels.

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  • In certain cases, however, the walls of the oesophagus appear to be very closely applied to the muscular body-wall and this vascular space thereby considerably reduced.

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  • 18, in the Heteronemertines the lateral stems, while entirely uniform all through the posterior portion of the body, no longer individually exist in the oesophageal region, but here dissolve themselves into a network of vascular spaces surrounding this portion of the digestive tract.

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  • The circulatory system of Carinella is considerably different, being more lacunar and less restricted to definite vascular channels.

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  • The vascular system is entirely closed.

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  • In origin the vascular system is due to a fusion of spaces which arise in the mesoblast of the larva.

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  • As a rule these organs only extend a short way along the anterior end of the body, a concentration which we may associate with the development of a vascular system I--- to bring the products of excretion to a fixed spot.

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  • There are no specialized sense-organs or vascular or respiratory systems. There is a wide body-cavity, but as this has no connexion with the renal or reproductive organs it cannot be regarded as a coelom, but probably is a blood-space or haemocoel.

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  • Specimens of flowering plants and vascular cryptograms are generally mounted on sheets of stout smooth paper, of uniform quality; the size adopted at Kew is 17 in.

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  • 4 About 310 species of vascular plants are found, of which about forty species are American, forty-four European-Asiatic, fifteen endemic, and the rest common both to America and Europe or Asia.

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  • It seems likely that the coelomic pore-canals were originally excretory organs, but in the existing Enteropneusta the pore-canals (especially the collar canals) have, as we have seen, acquired new functions or become vestigial, and the function of excretion is now mainly accomplished by a structure peculiar to the Enteropneusta called the glomerulus, a vascular complex placed on either side of the anterior portion of the stomochord, projecting into the proboscis-coelom.

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  • The vascular system itself is quite peculiar, consisting of lacunae and channels destitute of endothelium, situated within the thickness of the basementmembrane of the body-wall, of the gut-wall and of the mesenteries.

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  • The vascular system does not readily lend itself to morphological comparison between such widely different animals as Balanoglossus and Amphioxus, and the reader is therefore referred to the memoirs cited at the end of this article for further details.

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  • Correlated with the presence of the genital pleurae there is a pair of vascular folds of the basement membrane proceeding from the dorsal wall of the gut in the postbranchial portion of the branchio-genital region, and from the dorsal angles made by the pleural folds with the body-wall in the pharyngeal region; they pass, in their most fully developed condition, to the free border of the genital pleurae.

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  • These vascular membranes are called the lateral septa.

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  • On the inner surface of both valves several well-defined muscular, vascular and ovarian impressions are observable; they form either indentations of greater or less size and depth, or occur as variously shaped projections.

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  • 22) is hollow, and it contains a diverticulum "' s from the coelom, a branch of the vascular system, a nerve and some muscle fibres.

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  • This sinus is continued round the oesophagus as the peri-oesophageal sinus, and thus the whole complex of the small arm-sinus has the relations of the so-called vascular system of a Sipunculid.

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  • There is thus a vascular ring around the oesophagus.

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  • The vascular system is highly developed (in the non-degenerate forms); large arterial branches closely accompany or envelop the chief nerves; capillaries are well developed.

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  • The pathology of intra-cardiac and vascular murmurs has also been inquired into experimentally, the general impression being that these abnormal sounds result, in most cases at least, from the production of a sonorous liquid vein.

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  • The extreme development of the muscles in the weightlifting athlete and in the arm of the blacksmith is the result of increased functional activity with a corresponding increase in the vascular supply; this exercise may produce an over-development so excessive as to be classed as abnormal.

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  • There is thus brought into play a series of processes on the part of the tissues - the vascular inflammatory changes - which is really the first move to neutralize the malign effects.

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  • The vascular changes are practically absent in healing by first intention.

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  • These vascular buds grow out in various directions as little solid projections of cells; they then become channelled and form the new but temporary meshwork.

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  • By these processes we reach the stage where the fibrin mass and damaged tissues have been completely removed, and replaced by a temporary vascular and cellular tissue, known as granulation tissue (fig.

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  • - Healing abscess showing a wall of young cellular and vascular granulation tissue, which separates the pus area (top of Fig.) from the muscle fibres seen at lower part of Fig.

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  • This reaction is carried out by the mobile phagocytes sometimes alone, sometimes with the aid of the vascular phagocytes, or of the nervous system."

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  • The discoveries of the separate paths of sensory and motor impulses in the spinal cord, and consequently of the laws of reflex action, by Charles Bell and Marshall Hall respectively, in their illumination of the phenomena of nervous function, may be compared with the discovery in the region of the vascular system of the circulation of the blood; for therein a key to large classes of normal and aberrant functions and a fertile principle of interpretation were obtained.

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  • Many other diseases formerly regarded as primarily diseases of the nervous system are not such; but, by means of agents either introduced into the body or modified there, establish themselves after the affinities of these in contiguous associated parts of the structure, as in vascular, membranous or connective elements, or again in distant and peripheral parts; the perturbations of nervous function being secondary and consequential.

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  • In heart disease the chief work of the latter half of the 19th century was, in the first quarter, such clinical work as that of William Stokes and Peter Mere Latham (1789-1875); and in the second quarter the fuller comprehension of the vascular system, central and peripheral, with its cycles and variations of blood pressure, venous and arterial.

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  • Vascular plants 154 1035 2743

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  • The vascular plants already described number about 1500 species.

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  • They possess a modified anterior end, frequently with special sense organs, forming a head, a segmented nervous system, consisting of a pair of anterior, dorsally-placed ganglia, a ring surrounding the A ? ??° D B L/ alimentary canal, and a double ventral ganglionated chain, a definite vascular system, an excretory system consisting of nephridia, and paired generative organs formed from the coelomic epithelium.

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  • There is no trace of a true vascular system.

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  • In the latter case they invade cells of a leucocytic or phagocytic character as a rule; Leishman's form is particularly abundant in large macrophageal cells originating from the vascular endothelium of the spleen (fig.

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  • There are no pores in the foot or elsewhere in Lamellibranchia by which water can pass into and out of the vascular system, as formerly asserted.

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  • ab, ac, ad, Three pit-like depressions in the median line of the foot supposed by some writers to be pores admitting water into the vascular system.

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  • i [3], [5]) are highly vascular flat processes richly supplied with nerves.

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  • The Molluscan ctenidium is typically a plume like structure, consisting of a vascular axis, on each side of which is set a row of numerous lamelliform or filamentous processes.

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  • Classification Of Lamellibranchia The classification originally based on the structure of the gills by P. Pelseneer included five orders, viz.: the Protobranchia in which the gill-filaments are flattened and not reflected; the Filibranchia in which the filaments are long and reflected, with non-vascular junctions; the Pseudo-lamellibranchia in which the gill-lamellae are vertically folded, the interfilamentar and interlamellar junctions being vascular or non-vascular; the Eulamellibranchia in which the interfilamentar and interlamellar junctions are vascular; and lastly the Septibranchia in which the gills are reduced to a horizontal paltition.

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  • Branchial filaments united by vascular interfilamentar junctions and vascular interlamellar junctions; the latter contain the afferent vessels.

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  • Posteriorly, at what is known as the root of the penis, the two corpora cavernosa diverge, become more and more fibrous in structure, and are attached on each side to the rami of the ischium, while the corpus spongiosum becomes more vascular and enlarges to form the bulb.

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  • is formed, which is called the mesoderm, and gives rise to the muscular and connective tissues to the vascular system, and to the excretory and generative organs.

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  • (1875); " Note on the Coelom and Vascular System of Mollusca and Arthropoda," Quart.

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  • airArtv), a vascular organ situated on the left side of the abdomen (see DUCTLESS GLANDS).

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  • The stomach is formed upon much the same principle as that of the horse or rhinoceros, but is more elongated transversely and divided by a constriction into two cavities - a large left cul de sac, lined by a very dense white epithelium, and a right pyloric cavity, with a thick, soft, vascular lining.

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  • The heart and vascular system are similar to those of the Neomeniomorpha, the only important differences being that the ventricle is nearly free in the pericardial cavity, and that the latter is traversed by the retractor muscles of the gills.

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  • The typical foliage leaf consists of several layers, and amongst vascular plants is distinguishable into an outer layer (epidermis) and a central tissue (parenchyma) with fibro-vascular bundles distributed through it.

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  • In vascular acotyledonous plants there is frequently a tendency to fork exhibited by the fibro-vascular bundles in the leaf; and when this is the case we have f ork-veined leaves.

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  • The water taken up by the root from the soil contains nitrogenous and mineral salts which combine with the first product of photo-synthesis - a carbohydrate - to form more complicated nitrogen-containing food substances of a proteid nature; these are then distributed by other elements of the vascular bundles (the phloem) through the leaf to the stem and so throughout the plant to wherever growth or development is going on.

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  • When the vascular bundles reach the base of the lamina they separate and spread out in various ways, as already described under venation.

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  • In some Australian acacias, and in some species of Oxalis and Bupleurum, the petiole is flattened in a vertical direction, the vascular bundles separating immediately after quitting the stem and running nearly parallel from base to apex.

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  • The vascular bundles and cellular tissue are sometimes developed in such a way as to form a circle, with a hollow in the centre, and thus give rise to what are called fistular or hollow leaves, as in the onion, and to ascidia or pitchers.

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  • It resembles Dinophilus in the possession of a ventral pharyngeal pouch (which bears teeth in Histriodrilus only), the small number of segments, and absence of distinct septa, the absence of a vascular system, the presence of distinct ganglia on the ventral nerve cords, and of small nephridia which do not appear to open internally.

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  • This system is in no true sense a vascular system; there are no capillaries, and the fluid it contains, which is corpusculated, can hardly have a respiratory or nutritive function.

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  • g, Vascular spaces in tentacular cavity of the tentacular crown into vascular spaces.

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  • The vascular system has attained the highest state of development of all reptiles.

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