The whole of the tissue of the plant is formed by the division of this apical cell.
In the polyp the nervous tissue is always in the form of a scattered plexus, never concentrated to form a definite nervous system as in the medusa.
You were lucky and there was no torn tissue or fractures.
A small packet wrapped in tissue fell to her lap.
Next the larvae make their way into the connective tissue in the pro-thorax, and ultimately bore a channel into the base of the piercing apparatus and come to rest between the hypopharynx and the labium.
The ectoderm furnishes the general epithelial covering of the body, and the muscular tissue, nervous system and sense-organs.
Vacuolated tissue of pharyngeal wall, the so-called " pleurochords " of Masterman.
Pulling out a tissue he handed it to her.
Carmen wiped Destiny's face and eyes with the cool rag and used a tissue to wipe her nose.
Opening it, she removed a tissue and wiped the tears from her face.
And the botanist who finds that the apple falls because the cellular tissue decays and so forth is equally right with the child who stands under the tree and says the apple fell because he wanted to eat it and prayed for it.
Filaria medinensis - the Guinea worm - is parasitic in the subcutaneous connective tissue of man (occasionally also in the horse).
She grabbed a tissue from the box on the counter and blew her nose.
This one slid through the lemon like it was tissue paper and pricked her finger on the other side.
of the cell-wall (which is secreted by the living cell-body) the protoplasm dies, and a tissue in which this has occurred consists solely of the dead framework of cell-walls, enclosing in the cavities, originally occupied by the protoplasm, simply water or air.
The nervous system of the medusa consists of sub-epithelial ganglion-cells, which form, in the first place, a diffuse plexus of nervous tissue, as in the polyp, but developed chiefly on the subumbral surface; and which are concentrated, in the second place, to form a definite central nervous system, never found in the polyp. In Hydromedusae the central nervous system forms two concentric nerverings at the margin of the umbrella, near the base of the velum.
I found surprises, not in the stocking only, but on the table, on all the chairs, at the door, on the very window-sill; indeed, I could hardly walk without stumbling on a bit of Christmas wrapped up in tissue paper.
She daubed her eyes with a tissue and swallowed a sob - if she could speak the words.
She snatched a tissue from the jeweled box on her desk and buried her nose into its softness.
In all cases, while the internal threads which bear the cortical branches consist of elongated cells with few chromatophores, and no doubt serve mainly for conduction of food substances, the superficial cells of the branches themselves are packed with chromatophores and form the chief assimilating tissue of the plant.
a meristematic (cell-dividing) region occupying the whole of a certain transverse zone of the thallus, and cutting off new cells to add to the permanent tissue on both sides.
Blowing it on a tissue, she rang the door bell.
Lori thanked her for the tissue and wiped her eyes again.
The adult worm, which is of extremely minute size, the male being only Fi l sth and the female s of an inch in length inhabits the alimentary canal of man and many other carnivorous mammalia; the young bore their way into the tissues and become encysted in the muscles - within the muscle-bundles according to Leuckart, but in the connective tissue between them according to Chatin and others.
The muscular tissue consists primarily of processes from the bases of the epithelial cells, processes which are contractile in nature and may be distinctly striated.
The tentacles are always solid, containing an axis of endoderm-cells resembling notochordal tissue or plantparenchyma, and are but moderately flexible.
The tissue developed to meet the demands for conduction in such cases always shows some of the characters described.
"Linda says you can call her whenever you want," Lon said, handing Sofia a tissue with a phone number and smiley face written on it.
She blew her nose and threw the tissue in the trash.
She frantically threw her purse open, searching for a tissue, but a violent sneeze ripped through her lungs so quickly she barely had time to cover her mouth with her hand.
She plucked a tissue from the box on the counter and blew her nose.
external epithelium is flat on the ex-umbral surface, more columnar on the sub-umbral surface, where it forms the muscular tissue of the sub-umbrella and the velum.
In places the nematocysts may be crowded so thickly as to form a tough, supporting, " chondral " tissue, resembling cartilage, chiefly developed at the margin of the umbrella and forming streaks or bars supporting the tentacles (" Tentakelspangen," peronia) or the tentaculocysts (" Gehorspangen," otoporpae).
ia.Examples of the differentiation of the tissue of plants.
In addition to the cell types described, it is a very common occurrence in these bulky forms for rhizoid-like branches of the cells to grow out, mostly from the cells at the periphery of the medulla, and grow down between the cells, strengthening the whole tissue, as in the Rhodophyceae.
Darkyn was known for going through them like tissue paper.
The muscle-fibres arise as processes from the bases of the epithelial cells; such cells may individually become sub-epithelial in position, as in the polyp; or, in places where muscular tissue is greatly developed, as in the velum or sub-umbrella, the entire muscular epithelium may be thrown into folds in order to increase its surface, so that a deeper sub-epithelial muscular layer becomes separated completely from a more superficial bodyepithelium.
Maas in Results of In its arrangement the muscular tissue the "Albatross " Expedition, forms two s stems: the one composed Museum of Comparative Y P Zoology, Cambridge, Masse, of striated fibres arranged circularly, that U.S.A. is to say, concentrically round the central FIG.
Prolongations from the rim of chondral tissue may form clasps or peronia supporting the tentacles.
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.
The properties of podophyllin resin vary with the reaction of the tissue with which it is in contact; where this is acid the drug is inert, the picro-podophyllin being precipitated.
The mesogloea in the hydropolyp is a thin elastic layer, in which may be lodged the muscular fibres and ganglion cells mentioned above, but which never contains any connective tissue or skeletogenous cells or any other kind of special mesogloeal corpuscles.
In such cases the characters of the adult tissue clearly depend solely upon the characters of the cell-walls, and it is usual in plant-anatomy to speak of the wall with its enclosed cavity as the cell, and the contained protoplasm or other substances, if present, as cell-contents.
A specialized conducting tissue of this kind, used mainly for transmitting organic substances, is always developed in plants where the region of assimilative activity is local in the plant-body, as it is in practically all the higher plants.
The cells Cell and are commonly joined end to end in simple or branched Tissue filaments.
Such a system is called a tissuesystem, the word tissue being employed for any collection of cells with common structural, developmental, or functional characters to which it may be conveniently applied.
F, Section through the surface tissue of the Brown Alga Cutleria multifida, showing the surface layer of assimilating cells densely packed with phaeoplasts.
She started to cry again and Carmen pulled a fresh tissue from her purse.
The embryo consists of an axis bearing two or more cotyledons and ending below in a radicle; it lies in a generally copious food-storing tissue (endosperm) which is the remains of the female prothallus.
In many Laminariaceae the thallus also grows regularly in thickness by division of its surface layer, adding to the subjacent permanent tissue and thus forming a secondary meristem.
Carmen grabbed a tissue from the table next to the bed and wiped Destiny's nose.
After he recovered from the stabbing, the Doctor said he had scar tissue and would be susceptible to pneumonia in the injured lung.
Tears flooded her eyes and she dug in her purse for a tissue.
She sniffed and wiped her eyes with a well-used tissue.
Carmen blew her nose and grabbed another tissue.
It is probable that the parasite is then transferred to the alimentary canal of man by means of drinking-water, and thence makes its way to the subcutaneous connective tissue.
The adult stages are found in the sub-peritoneal connective tissue.
In this way we may distinguish, first, vegetative reproduction, the result of discontinuous growth of the tissues and cell-layers of the body as a whole, leading to (I) fission, (2) autotomy, or (3) vegetative budding; secondly, germinal reproduction, the result of the reproductive activity of the archaeocytes or germinal tissue.
A solid fungal body may usually be seen to consist of separate hyphae, but in some cases these are so bent and closely interwoven that an appearance like that of ordinary parenchymatous tissue is obtained in section, the structure being called pseudo parenchyrna.
The internal tissue of the body of the solid higher Fungi, particularly the elongated stalks (stipes) of the fructifications of the Agarics, consists of hyphae running in a longitudinal direction, which no doubt serve for the conduction of organic food substances, just as do the trumpet-hyphae, similar in appearance, though not in origin, of the higher Brown Seaweeds.
In the higher forms a storage and a mechanically-strengthening system may also be developed, and in some aerial Fungi an external protective tissue.
The frondose (thalloid) Jungermanniales show no such differentiation of an assimilating tissue, though the upper cells of the thallus usually have more chlorophyll than the rest.
Such differentiated water-conducting cells we call hydroids, the tissue they form hydrom.
The latter are plates of green tissue one cell thick, while the stem consists of uniform more or less elongated cylindrical cells.
In a few cases there is a special surface or epidermal layer, but usually all the outer layers of the stem are composed of brown, thick-walled, lignified, prosenchymatous, fibre-like cells forming a peripheral stereom (mechanical or supporting tissue) which forms the outer cortex.
In the highest family of mosses, Polytrichaceae, the differentiation of conducting tissue reaches a decidedly higher level.
In addition to the water-conducting tissue or hydrom there is a welldeveloped tissue (leptom) inferred to be a conducting channel for organic substances.
Besides the hydrom and leptom, and situated between them, there is a tissue which perhaps serves to conduct soluble carbohydrates, and whose cells are ordinarily full of starch.
These three concentric tissue mantles are evidently formed by the conjoined bases of the leaf traces, each of which is composed of the same three tissues.
In Cat harinea undulata the central h drom cylinder of the aerial stem is a loose tissue, its interstices being filled up with thin-walled, starchy parenchyma.
Besides this there is usually a living conducting tissue, sometimes differentiated as leptom, forming a mantle round the hydrom, and bounded externally by a more or less well-differentiated endodermis, abutting on an irregularly cylindrical lacuna; the latter separates the central conducting cylinder from the cortex of the seta, which, like the cortex of the gametophyte stem, is usually differentiated into an outer thick-walled stereom and an inner starchy parenchyma.
trace a three-fold division of tissue systems, a division of which there are indications among the lower plants, and which is the expression of the fundamental conditions of the evolution of a bulky differ- Tissue entiated plant-body.
On the other hand, we have (2) an internal differentiation of conducting tissue, the main features of which as seen in the gametophyte of Bryophytes have already been fully described.
In the Vascular Plants this tissue is collectively known as the vascular system.
The remaining tissue of the plant-body, a tissue that we must regard phylogenetically as the remnant of the undifferentiated tissu~ of the primitive thallus, but which often undergoes further different,iation of its own, the better to fulfil its characteristically vital functions for the whole plant, is known, from its peripheral position in relation to the primitively central conducting tissue, as (3) the cortex.
The guard-cells contain chlorophyll, which is absent from typical epidermal cells, the latter acting as a tissue for water storage.
In a second type they are situated at the ends of tracheal strands and consist of groups of richly protoplasmic cells belonging to the epidermis (as in the leaves of many ferns), or to the subjacent tissue (the commonest type in flowering plants); in this last case the cells in question are known as epithem.
At the apex of a root, covering and protecting th~ delicate tissue of the growing point, is a special root-cap consistinf of a number of layers of tissue whose cells break down into mucilagi towards the outer surface, thus facilitating the passage of the ape~ as it is pushed between the particles of soil.
The cortex, as has been said, is in its origin the remains of th~ primitive assimilating tissue of the plant, after differentiatioi of the surface layer and the conducting system.
In the leafy shoot this function is mainly localized in the cortical tissue of the leaves, known as mesophyll, Mesophyli.
The stomata are in direct communication with the ample system of intercellular spaces which is found in the loosely arranged mesophyll (spongy tissue) on that side.
This is the main transpiring tissue, and is protected from direct illumination and consequent too great evaporation.
The main assimilating tissue, on the other hand, is under the upper epidermis, where it is well illuminated, and consists of oblong cells densely packed with chloroplasts and with their long axes perpendicular to the surface (palisade tissue).
c/i, epidermis; st stoma; me,, mesophyil; pal, palisade; spa, spongy tissue; Isp, inteicellular space; wi., water tissue; x, xylem; p/i, phioem; Phil, phloeoterma; sri, scierenchyma.
The leaves of shade plants have little or no differentiation of palisade tissue.
In fleshy leaves which contain a great bulk of tissue in relation to their chlorophyll content, the central mesophyll contains little or no chlorophyll and acts as waterstorage tissue.
In the larger veins of the leaf especially in the midrib, in the petiole, and in the young stem, a1 extremely frequent type of mechanical tissue is collenchyma.
This consists of elongated cells with cellulose walls, which are locall~ thickened along the original corners of the cells, reducing the lumer to a cylinder, so that a number of vertical pillars of cellulose con nected by comparatively thin walls form the framework of th~ tissue.
This tissue remains living and is usually formed quiti early, just below the epidermis, where it provides the first periphera support for a still growing stem or petiole.
The whole tissue system is known as the stelar system (from the way in which in primitive forms it runs through the whole axis of the plant in the form of a column).
This is a morphological term given to the particular~ type of hydrom found in both Pteridophytes and Phanerogams, together with the parenchyma or stereom, or both, included within the boundaries of the hydrom tissue strand.
The sieve-tubes, with their accompanying parenchyma or stereom, constitute the tissue called phloem.
c eun~7 Such an arrangement of vascular tissue is called radial, ~
The pericycle and mesocycle together form the conjunctive tissue of the stele in these simplest types.
When the diameter of the stele is greater, parenchymatous conjunctive tissue often occupies its centre and is frequently called the pith.
Where internal phloem is present this is separated from the internal endodermis by an endocycle or internal pericycle, as it is sometimes called, and from the xylem by an internal mesocyclethese two layers, together with the outer mesocycle and pericycle, constituting the conjunctive tissue of the now hollow cylindrical stele.
The centre of the S~hooo- stele is however often occupied by a large-celled pith resembling the cortex in structure, the cortex and pith ~ together being classed as ground tissue.
peristelar tissue; p.1.
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.
The vascular tissue is typically separable into distinct collateral bundles (figs.
13, 23), the xylem of which is usually wedgeshaped in cross-section with the protoxylem elements at the inner extremity, while the phloem forms a band on the outer side of the xylem, and separated from it by a band of conjunctive tissue (mesodesm).
When the pith is large celled, the xylems of the bundles are separated from it by a distinct layer of conjunctive tissue called the endocycle, and a similar layer, the pericycle, separates the phloem from the cortex.
The pericycle, medullary rays, endocycle and mesoderm all form parts of one tissue system, the external conjunctive, and are only topographically separable.
The external conjunctive is usually a living comparatively small-celled tissue, whose cells are consider ably elongated in the direction of the stem-axis and frequently contain abundant starch.
Each J~ 1 1 / Stelein bundle has its own ~ investment of tissue P corresponding with external conjunctive, and now called peridesm.
In some astelic L- ~ stems (Nymphaeaceae) the number of bundles is greatly increased and they are scattered throughout the ground tissue.
Annuiar vessel, superficially obvious order through & I,~iterceiiuIar canal, the conjunctive tissue of the stele, 1.
In other cases the reduction goes much further, till the endodermis eventually comes to surround nothing but an intercellular channel formed in place of the stelar tissue.
In certain families of Angiosperms a peculiar tissue, called laticiferous tissue is met with.
They possess a delicate Laticiferous layer of protoplasm, with numerous small nuclei lining Tissue the walls, while the interior of the tube (corresponding with the cell-vacuole) contains a fluid called latex, consisting of an emulsion of fine granules and drops of very various substances suspended in a watery medium in which various other substances (salts, sugars, rubber-producers, tannins, alkaloids and various enzymes) are dissolved.
The relation ~ of the laticiferous tissue to the assimi I lating cells under which they often end, and the fact that where this tissue is / richly developed the conducting paren ~ chyma of the bundles, and sometimes also 4 the sieve-tubes, are poorly developed, as well as various other facts, point to the conclusion that the laticiferous system has an important function in conducting plastic substances, in addition to acting as an excretory reservoir.
- Laticiferous tissue is of two kinds:
The epidermis in the stair and the surface layer of the root soon becomes differentiated froit the underlying tissue.
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.
In this tissue fresh bundles may become differentiated, and what remains of it becomes the rays of the fully-formed stele.
The young tissue of the stelar cylinder, in the case of the modified siphonostele characteristic of the dicotyledonous stem, differs from the adjoining pith and cortex in its narrow elongated cells, a difference produced by the stopping of transverse and the increased frequency of longitudinal divisions.
The protoxylem and protophloem are developed a few cells from the inner and outer margins respectively of the desmogen strand, the desmogenic tissue left over giving rise to the segments of endocycle and pericycle capping the bundle.
Sometimes development stops altogether, and a layer of undifferentiated parenchyma (the mesodesm) is left between them; or it may continue indefinitely, the central cells keeping pace by their tangential division with the differentiation of tissue on each side.
In this case the formation of the primary bundle passes straight over into the formation of secondary tissue by a cumbium, and no line can be drawn between the two processes.
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.
In such cases it is part of the peridesm or sheath of elongated narrowcelled tissue surrounding the individual bundle.
New tangential walls arise in the cells which are the seat of cambial activity, and an initial layer of cells is established which cuts off tissue mother-cells on the inside and outside, alternately contributing to the xylem and to the phloem.
A tissue mother-cell of the xylem may, in the most advanced types of Dicotyledons, give rise to(I) a tracheid; (2) a segment of a vessel; (3) a xylem-fibre; or (4) a vertical file of xylem-parenchyma cells.
A tissue mother-cell of the phloem may give rise to (i) a segment of a sieve-tube with its companion cell or cells; (2) a phloem fibre; (3) a single phloem-parenchyma (cambiform) cell, or a ve~rtical file of short parenchyma cells.
It is essentially a living tissue, and serves to place all the living cells of the secondary vascular tissues in communication.
This type is found in nearly all Pteridophytes and, so far as is known, in Cycadofihices, both in primary and secondary tissue.
in the primary and secondary tissue, is that the proteid cells of the phloem are here always sister-cells of the leptoids and are known as companion-cells.
The main feature is the development of special vascular stereom and storage tissue.
In some cases special secreting tissues, resin ducts, oil glands, laticiferous tissue, crystal sacs, &c., may be developed among the ordinary secondary vascular elements.
When the vascular tissue of such plants is arranged Camblum in separate bundles these are said to be closed.
In stems with open bundles the formation of cambium and secondary tissue may be confined to these, when it is sard to be entirely fascicular.
In that case either very little secondary tissue is formed, as in the gourds, some Ranunculaceae, &c., or a considerable amount may be produced (clematis, barberry, ivy).
The interfascicular cambium may form nothing but parenchymatous tissue, producing merely continuations of the primary rays.
In other cases a most intricate arrangement of secondary tissue masses is produced, quite impossible to interpret unless all stages of their development have been followed.
The cambium in the root, which is found generally in those plants which possess a cambium in the stem, always begins in the conjunctive tissue internal to the primary phloems, and Camblum forms new (secondary) phloem in contact with the In Roots primary, and secondary xylem internally.
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.
the cambium, and producing like the latter an external ~i, and an internal secondary tissue.
and the whole of the tissue it gives rise to is known as periderm.
The phellogen derives its name from the fact that its external product is the characteristic tissue known as cork.
The internal tissue formed by the phellogen is known as phelloderm, and consists usually of ordinary parenchyma.
In the former case the formation of phelloderm is trivial in amount; in the latter, considerable, since this tissue has to replace the cast-off cortex, as a metabolic and particularly a storage tissue.
supplementary vascular bundles, anomalous cambial zones, &c. It is often enormously developed and forms a very important tissue in roots.
In other cases, a similar formation of spongy but dead periderm tissue may occur for the same purpose in special patches, called pneumatodes, on the roots of certain trees living in marshy places, which rise above the soil in order to obtain air.
numerous, mainly German, workers, though no fundamentally new types of tissue have been discovered.
Fuchs and its allies, which form conspicuous members of the larger Algae, have their external cells much smaller, more closely put together, and generally much denser than the rest of their tissue.
They often cause a considerable hypertrophy of the tissue.
The swellings have been found to be due to a curious hypertrophy of the tissue of the part, the cells being filled with an immense number of minute bacterium-like organisms of V, X or Y shape.
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.
The root is continually growing and so the sensitive part is continually changing its composition, cells being formed, growing and becoming permanent tissue.
The active contraction of muscular tissue has no counterpart in the plant.
But the case is obviously different where a plant dies because some essential organ or tissue tract has been destroyed, and other parts have suffered because supplies are cut offe.g.
In a large number of cases, however, the disease is purely local, and does not itself extend far into the organ or tissue affected.
Sclerophyllous leaves are ually characterized by entire or sub-entire margins, a thick cuticle, riall but rarely sunken stomata, a we1l-developed and close-set ilisade tissue and a feeble system of air-spaces.
Strengthening tissue of all kinds (and sometimes even the phloem) is more or less rudimentary.
Switch plants, such as Retama Retam and broom (Cytisus scoparius), have reduced leaves and some assimilating tissue in their stems; and stomata occur in grooves on the stem.
In such leaves, there are a well-marked cuticle, a thick epidermis, a thick hypodermis at least on the upper side of the leaf, well-developed palisade tissue, and a poorly developed system of air-spaces.
their leaves and, to some extent, their stems have much water-storing tissue and few intercellular spaces.
Strengthening tissue is feebly developed.
Laticiferous Tissue.The laticiferous tissue consists of a network of branching or anastomosing tubes which contain a coagulable fluid known as latex.
There are two types of tissue: non-articulate and articulate.
(1882); On the Laticiferous Tissue of Man-rhot Glazsovii (the Ceark Rubber), Quart.
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).
They derive this moisture from the air by means of aerial roots, developed from the stem and bearing an outer spongy structure, or velamen, consisting of empty cells kept open by spiral thickenings in the wall; this sponge-like tissue absorbs dew and rain and condenses the moisture of the air and passes it on to the internal tissues.
The epidermis contains numerous groups of sense cells; beneath the epidermis there is rarely (Kynotus) an extensive connective tissue dermis.
The network is partly formed out of pigmented cells which are excavated and join to form tubes, the socalled botryoidal tissue, not found among the Rhynchobdellidae at all.
The main distinction is the occurrence in the tissue of the fruit, or beneath the rind, of clusters of cells filled with hard woody deposit in the case of the pear, constituting the "grit," while in the apple no such formation of woody cells takes place.
The foot of the limpet is a nearly circular disk of muscular tissue; in front, projecting from and raised above it, are the head and neck (figs.
On the whole the ganglia are strongly individualized in the Pectinibranchia, nerve-cell tissue being concentrated in the ganglia and absent from the cords.
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.
Adult without shell; a sub-epithelial pseudoconch formed by connective tissue; pallial cavity ventral.
This cavity contains an irregular mass of whitish tissue, the fat-body, consisting of fat-cells which undergo degradation and become more or less filled with urates.
It was found that the tissues were attacked by phagocytic cells that became enlarged and carried away fragments of the tissue; the cells were subsequently identified as leucocytes or blood-cells.
These do not take a direct part in the formation of the new tissue, but it is believed merely yield their surplus acquisitions, becoming ordinary blood-cells or disappearing altogether.
Examination showed that although the weevil attacked the young buds these did not drop off, but that a special growth of tissue inside the bud frequently killed the grub.
Also, inside the young bolls which had been pierced a similar poliferation or growth of the tissue was set up, which enveloped and killed the pest.
It then often retains its vitality for a long time, apparently crawling as if it were itself a worm, a phenomenon which is at least partially explained by the extraordinary development of nervous tissue, equally distributed all through the walls of the proboscis, and either united into numerous longitudinal nerve-stems (Drepanophorus, Amphiporus) or spread out into a uniform and comparatively thick layer (Cerebratulus, sp.).
Superiorly the sheath either closely adheres to the muscular bodywall, with which it may even be partly interwoven, or it hangs freely in the connective tissue which fills the space between the intestine and the muscular body-wall.
In Carinella, Cephalothrix, Polia and the Metanemertines the two tegumentary layers with their different glandular elements are fused into one; a thick layer of connective tissue is situated beneath them (instead of between them) and keeps the entire cutaneous system more definitely separate from the muscular (fi g s.
c, Cellular tissue of the integument; Bm, basement membrane; cire.
I, outer circular, and long., longitudinal layer of muscular tissue; circ. 2, long.
The connective tissue of the integument and basement membrane imperceptibly merges into that which surrounds the muscular bundles as they are united into denser and definite layers, and this is especially marked in those forms (Akrostomum) where the density of the muscular body-wall has considerably diminished, and the connective tissue has thus become much more prominent.
It can then at the same time be observed, too, that the compact mass of connective tissue (" reticulum," Barrois) which lies between the muscular bodywall and the intestine is directly continuous with that in which the muscular layers are embedded.
The omnipresence of this connective tissue tends to exclude the formation of any perivisceral body cavity in Nemertines.
In Polia the connective tissue enclosed in the external muscular layer is eminently vacuolar - all the intermediate stages between such cells in which the vacuole predominates and the nucleus is peripheral and those in which the granular protoplasm still entirely fills them being moreover present.
To it belong (a) superficial grooves or deeper slits situated on the integument near the tip of the head, (b) nerve lobes in immediate connexion with the nervous tissue of the brain, and (c) ciliated ducts penetrating into the latter and communicating with the former.
These posterior brain-lobes, which in all Heteronemertines are in direct continuity of tissue with the upper pair of principal lobes, cease to have this intimate connexion in the Metanemertini; and, although still constituted of (I) a ciliated duct, opening out externally, (2) nervous tissue surrounding it, and (3) histological elements distinctly different from the nervous, and most probably directly derived from the oesophageal outgrowths, they are nevertheless here no longer constantly situated behind the upper brain-lobes and directly connected with them, but are found sometimes behind, sometimes beside and sometimes before the brain-lobes.
Here the pits split into two, one part ending in a sac lined with sensory epithelium, and embedded in nervous tissue, the other projecting backwards as a long, glandular, blind canal.
For the Heteronemertines arguments have been adduced to prove that here they have the physiological significance of a special respiratory apparatus for the central nervous tissue, which in all these forms is strongly charged with haemoglobin.
Anteriorly it finally communicates with the lacunae just mentioned, which surround the oesophagus, bathe the posterior lobes of the brain, pass through the nerve ring together with the proboscidian sheath, and are generally continued in front of the brain as a lacunar space in the muscular tissue, one on each side.
CT, Connective tissue.
sub-cuticular tissue of the f, One of the retractors of the trunk and that of the pro g, A lemniscus.
Elastin occurs either as thick strands or as membranes; it constitutes the " elastic tissue " of the anatomist.
Latex, though chiefly secreted in vessels or small sacs which reside in the cortical tissue between the outer bark and the wood is also found in the leaves and sometimes in the roots or bulbs.
22) shows that it consists of a stout base, composed of a very hyaline connective tissue not uncommon in the tissues of the Brachiopoda, which is traversed by certain canals whose nature is considered below under the section (The Body Cavity) devoted to the coelom.
In Discinisca and Lingula there is further a lip-sinus or hollow system of channels which traverses the supporting tissue of the edge of the mantle and contains muscle-fibres.
The plexus of nerve-fibrils which underlie the ectoderm and are in places gathered up into nerves, and the great development of connective tissue, are worthy of notice.
Much of the latter takes the form of hyaline supporting tissue, embedded in which are scattered cells and fibres.
The lophophore and stalk are largely composed of this tissue.
Accordingly the diplostichous ommatoeum or soft tissue of the Arachnid's central eye should strictly be called " triplostichous," since the deep layer is itself doubled or folded.
The coils and branches of the tube are packed by connective tissue and blood spaces.
The entosternite was probably in origin part of the fibrous connective tissue lying close to the integument of the sternal surface - giving attachment to muscles corresponding more or less to those at present attached to it.
h, Epidermic cell-layer; mes, mesoblastic connective tissue; n, nerves; II, III, IV, V, depressions of the epidermis in each of which a cuticular lens will be formed.
- Section through a portion of the lateral eye of Limulus, showing three ommatidia - A, B and C. hyp, The epidermic cell-layer (so-called hypodermis), the cells of which increase in volume below each lens, 1, and become nerve-end cells or retinula-cells, rt; in A, the letters rh point to a rhabdomere secreted by the cell rt; c, the peculiar central spherical cell; n, nerve fibres; mes, mesoblastic skeletal tissue; ch, chitinous cuticle.
tiss, Connective tissue (mesomediately underlying the lens.
An internal skeletal plate, the so-called " entosternite " of fibrocartilaginous tissue, to which many muscles are attached, is placed between the nerve-cords and the alimentary tract in the prosoma of the larger forms (Limulus, Scorpio, Mygale).
5), Dracaena and Cordyline include arborescent species in which the stem increases in thickness continually by a centrifugal formation of new tissue; an extreme case is afforded by Dracaena Draco, the dragon-tree of Teneriffe.
The caseous necrosis of the implicated mass of lung tissue, and indeed of tubercles generally, is held to be, in great measure, the result of the necrotic influence of the secretions from the bacillus.
Disease we may define, accordingly, as any departure from the normal standard of structure or function of a tissue or organ.
- When the blood supply is entirely cut off from a tissue the tissue dies, and in the act of dying, or afterwards, it suffers certain alterations dependent upon its surroundings.
II.); that is to say, it dies and falls a prey to the organisms which excite putrefaction, just as would happen to any other dead animal tissue were it unconnected with the body.
Muscle and white fibrous tissue follow next in order, while elastic tissue and bone are the last to show signs of disintegration.
The temperature at which the limb is kept, no doubt, favours and hastens the natural process of destruction, so that putrefaction shows itself sooner than would be the case with a dead tissue removed from the body and kept at a lower temperature.
Nevertheless, gangrene is nothing more or less than the putrefactive fermentation of an animal tissue still attached to the body.
If the amount of liquid contained in the tissue be small in quantity the part mummifies, giving rise to what is known as " dry gangrene."
Should the portion of tissue deprived of its circulation be contained in an internal organ, as is so often the case where the obstruction in the artery is due to embolism, it becomes converted into what is known as an " infarction."
If absorption be not complete the mass undergoes caseation and becomes surrounded by a capsule of fibrous tissue - being sharply cut off from the healthy tissue.
If, on the other hand, any pathogenic organisms be present the results are disastrous because the tissue, deprived of its nervous trophic supply, has greatly lessened resistance.
It is much more likely, as Verworn alleges, that the nerves which influence the characteristic function of any tissue regulate thereby the metabolism of the cells in question - in other words, that every nerve serves as a trophic nerve for the tissues it supplies.
The effect of overwork upon an organ or tissue varies in accordance with (a) the particular organ or tissue concerned, (b) the amount of nourishment conveyed to it, and (c) the power of assimilation possessed by its cells.
The term hypertrophy is used when the individual tissue elements become bigger to meet the demands of greater functional activity; hyperplasia, if there is an increase in the number of these elements; and pseudo-hypertrophy, when the specific tissue element is largely replaced by another tissue.
Should there be much loss of tissue of an organ, the cells of the remaining part will enlarge and undergo an active proliferation (hyperplasia) so that it may be made up to the original amount.
Increased work thrown on to a tissue may produce hypertrophy, but, if this excessive function be kept up, atrophy will follow; even the blacksmith's arm breaks down owing to the hypertrophic muscle fibres becoming markedly atrophied.
Injury and loss of tissue are usually followed by repair, and both the destructive and reparative changes are, as a rule, classified under the term inflammation.
If the abscess be deeply situated in some tissue and not able to open on to a free surface so allowing the contents to be drained off, the phagocytic cells play a very prominent part in the resolution of the abscess.
Then they develop .definite fibrils which differentiate into fibrous laminae forming a zone which shuts off the abscess from the healthy tissue and so prevents the further invasion and injurious effects of the microorganism.
IV.), that of " sclerosis " is used when such a deposition of fibrous tissue occurs within the central nervous system.
Tumours Or New Growths The various definitions of the term " new growth " leave us with a definite conception of it as a new formation of tissue which appears to originate and to grow independently.
According to the hypothesis of Waldeyer and Thiersch there is perfect equilibrium between the normal epithelium and its supporting structure, the connective tissue, but with advancing age this balance is upset owing to the connective tissue gradually losing its restraining power.
The separated cells become intermingled with other tissue elements amongst which they lie dormant with their inherent power of proliferation in abeyance.
He holds that new growths arise, both before birth or at any subsequent period of life, by the separation of cells or clumps of cells from their normal position, and that in health there is a balance between the various tissues and tissue elements regulated by what he calls the " tissue-tension " of the part, i.e.
Then we have Beard's " germ-cell " hypothesis, in which he holds that many of the germ-cells in the growing embryo fail to reach their proper position - the generative areas - and settle down and become quiescent in some somatic tissue of the embryo.
They are direct lineal descendants of the cells introduced, and are in no way formed from the tissue cells of the host in which they are placed and grow.
Not only is this true of epithelial cells, but - the connective tissuecells of the supporting structure of cancerous growth, after repeated transplantation, may become so altered that a gradual evolution of apparently normal connective tissue into sarcomatous elements takes place, these giving rise to " mixed tumours."
The fact that it is possible to propagate these cells of one animal for years in other animals of the same species, without any loss of their vegetative vitality, suggests that this continued growth is kept up by a growth-stimulating substance present in the proper species of animal; this substance, however, has not the power of transforming the normal tissue into a cancerous one.
- Symmetrical gangrene of toes (3 months' duration), showing the sharp " line rof demarcation " between the mummified toes and the more healthy tissue.
i iuroblasts in young temporary granulation tissue.
It is from these cells the permanent fibrous tissue is formed.
- Scar tissue in a healed wound.
lobular cirrhosis, of ` Gin-drink, I's Li, showing well-formed fibrous overgrowth which has divided up the liver tissue into irregular masses and caused atrophic and d egenerative changes in the liver cells.
- 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.
- Chronic interstitial myocarditis, showing the muscle fibres in the heart wall being separated and becoming atrophied by a slow fibrous overgrowth of the connective tissue.
- Granulauun tissue showing the character and relation of the cellular elements to the new blood-vessels in the young temporary tissue.
It may merely act locally in some way, and so render that part susceptible to unknown tissue stimuli which impart to the cells that extraordinary power of proliferation characteristic of new growth.
A defect in co-ordination allows the stimulated active vegetative cellular elements, or the more fully differentiated tissue, to over-develop and so form tumours, simple or malignant.
Other Tissue Products Mucoid.
The connective tissue is supplied normally with a certain amount of these mucinoid substances, no doubt acting as a lubricant.
In the wasting of the thyroid gland in myxoedema, or when the gland is completely removed by operation, myxomatous areas are found in the subcutaneous tissue of the skin, nerve-sheaths, &c.
In acute and chronic alcoholism, in phthisis, and in other diseases this fatty condition may be very extreme, and is commonly found in association with other tissue changes, so that probably we should look on these changes as a degeneration.
Adiposity or obesity occurs when we have an excessive amount of fat stored in the normal connective-tissue areas of adipose tissue.
Note the sharp line of demarcation between the growth and the tissue in which it is growing.
A simple tumour composed of well-differentiated fibrous tissue.
The fibres are arranged in irregular bundles forming a dense firm tissue.
These are pressed upon and become atrophied, and may ultimately be replaced by adipose tissue.
These soluble salts combine with the albumins in the body, and are deposited as minute granules of silver albuminate in the connective tissue of the skin papillae, serous membranes, the intima of arteries and the kidney.
It also occurs in bones and elastic tissue, but is not present in the normal human liver.
drill-bones) may develop in a soft tissue with no natural bone-forming tendencies, as a result of interrupted pressure, or a fatty tumour may arise in the midst of the natural subcutaneous fat in the same circumstances.
It is invariably the result of some cause acting generally, such as renal disease, valvular defect of the heart, or an impoverished state of the blood; while a mere oedema is usually dependent upon some local obstruction to the return of blood or lymph, or of both, the presence of parasites within the tissue, such as the filaria sanguinis hominis or trichina spiralis, or the poisonous bites of insects.
In a given case of anasarca due to a cause acting generally, it will be found that the liquid of the pleural cavity always contains the highest percentage of proteid, that of the peritoneal cavity comes next, that of the cerebral ventricles follows this, and the liquid of the subcutaneous areolar tissue contains the lowest.
It may be asked, however, whether a dropsical tissue is being held in a high state of nutrition, and whether, on the contrary, the presence of lymph in excess in its interstices does not tend to impair its vitality rather than to lend it support.
Bainbridge suggests that a retention of metabolic products may cause the oedema in renal disease, Bradford having previously shown that loss of a certain amount of renal tissue caused retention of metabolic products in the tissues.
As sodium chloride is one of the most permeable of crystalloids it seems strange that damage to the renal tissue should impede its excretion.
i.; Afanassieff, " Granulation Tissue and Infection," Centralbl.
418, also, Manual of General Pathology (London, 1898); Loeb, " Certain Activities of the Epithelial Tissue of Skin of Guinea-pig, &c.," Johns Hopkins Hosp. Bull., Balt.
Haller's definition of irritability as a property of muscular tissue, and its distinction from sensibility as a property of nerves, struck at the root of the prevailing hypothesis respecting animal activity.
It is desultory to a degree; it is a base libel on religion and history; it differs from its model Ariosto in being, not, as Ariosto is, a mixture of romance and burlesque, but a sometimes tedious tissue of burlesque pure and simple; and it is exposed to the objection - often and justly urged - that much of its fun depends simply on the fact that there were and are many people who believe enough in Christianity to make its jokes give pain to them and to make their disgust at such jokes piquant to others.
The surrounding tissue enlarges, so that the spots appear as if sunk in depressions, and bear a considerable resemblance to hailstone wounds.
The mass of the body consists of richly branched stellate cells - the mesenchyma - and imbedded in this plasmic tissue are the nervous, excretory, muscular and generative organs.
Cysticercus cellulosae may be comparatively innocuous in a muscle or subcutaneous tissue, but most hurtful in the eye or brain.
Too rapid drying of the outer tissue of the leaf leads to the formation of " white veins," which injure leaves required for wrapper purposes, otherwise it is not important.
Green in the first chapter of his Prolegomena to Ethics, involves the absurdity that our whole experience is a tissue of relations with no points of attachment on which the relations depend.
Between the blind gut and the cuticle is a reticular branched tissue which forms the chief substance of the body.
As in other Platyelmia the elements of this tissue undergo the most varied differentiation.
It escapes into the adjacent tissue and there gives rise either to one or more generations of rediae or at once to a new type of organism - the cercaria.
8 A, 9 A), but in many Cheilostomes the frontal surface is protected by a calcareous shield, which grows from near the free edges of the vertical walls and commonly increases in thickness as the zooecium grows older by the activity of the "epitheca," a layer of living tissue outside it.
This tissue is continuous from zooecium to zooecium (After Allman.) FIG.
The venom is generally introduced into the subcutaneous tissue, whence it reaches the general circulation by absorption through the lymph and blood-vessels.
The animal and the plant alike require food to repair waste, to build up new tissue and to provide material which, by chemical change, may liberate the energy which appears in the processes of life.
The continued use of large doses of alcohol produces chronic gastritis, in which the continued irritation has led to overgrowth of connective tissue, atrophy of the gastric glands and permanent cessation of the gastric functions.
intoxication), chronic alcoholism, delirium tremens, and all the countless pathological changes - extending to every tissue but the bones, and especially marked in the nervous system - which alcohol produces.
animal tissue from which the insect is sucking.
Under- (Radicola) of Phylloxera, with proneath, between the legs, lies the boscis inserted into tissue of root rostrum, which reaches back to of vine.
1791), "tissue of absurdities" though the queen thought it, and much as she would have preferred a bolder course, she considered that in the circumstances the king was bound to accept it in order to inspire confidence.'
Auditory bulla filled with honeycombed bony tissue.
Correlated with their life in dry situations, the bulk of the tissue is succulent, forming a water-store, which is protected from loss by evaporation by a thickly cuticularized epidermis covered with a waxy secretion which gives a glaucous appearance to the plant.
For this purpose the skin is tied by connecting fibres of white fibrillar tissue to the deep layer of the dermis along the lateral and lower edges of the palmar fascia and to the sheaths of the flexor tendons.
Other constituents are cholesterol (0.461.32%), traces of calcium, magnesium, sodium, chlorine and bromine, and various aliphatic amines which are really secondary products, being formed by the decomposition of the cellular tissue.
The largest class are the unilocular, or simple, external galls, divided by Lacaze-Duthiers into those with and those without a superficial protective layer or rind, and composed of hard, or spongy, or cellular tissue.
It has long been known, and is now generally recognized, that a gall can only be produced when the tissue of a plant is interfered with during, or prior to, the actual development of the tissue.
Rare bulbs may be wrapped singly in tissue paper for storing.
It readily dissolves the epidermis of the skin and many other kinds of animal tissue - hence the former application of the "sticks" in surgery.
The stomach is generally large; its wall consists of a layer of very large ciliated cells, which often contain fat globules and yellowish-green or brown particles, and outside these a connective tissue membrane; muscular fibrillae have also been described.
The end of the evolution process is the production of a "social tissue" which will be "vitally efficient."
This fissure represents the hilum of the liver, and contains the right and left hepatic ducts and the right and left branches of the hepatic artery and portal vein, together with nerves and lymphatics, the whole being enclosed in some condensed subperitoneal tissue known as Glisson's capsule.
The liver cells, therefore, are entodermal, but the supporting connective tissue mesodermal from the septum transversum.
ct, Interlobular connective tissue forming the capsules of the lobules.
The new fibrous tissue which is developed throughout the liver, as the result of the chronic inflammation, causes general enlargement of the liver with, perhaps, nausea, vomiting and jaundice.
Later the new fibrous tissue undergoes contraction and the liver becomes smaller than natural.
Nevertheless the filament is a complete tube formed of chitinous substance and clothed externally by ciliated epithelium, internally by endothelium and lacunar tissue - a form of connective tissue - as shown in fig.
if, Fibroussub-epidermic tissue.
lac, Lacunar tissue.
f, Constituent open between the filaments in filaments; trf, fibrous tissue of the irregular rows separated horitransverse inter-filamentar junczontally by the transverse intertions; v, blood-vessel ilj, Interfilmentar junctions.
Deep to these is the ovarian stroma, composed of fibrous tissue, and embedded in it are numerous nests of epithelial cells, the Graafian follicles, in various stages of development.
The mucous membrane is raised into a series of transverse folds or rugae, and between it and the muscular wall are plexuses of veins forming erectile tissue.
Cavity of body Cavity of cervix elevation in front of the pubic bones caused by a mass of fibrofatty tissue; the skin over it is covered by hair in the adult.
The convolutions are held together by the pelvic cellular tissue, and by involuntary muscle continuous with that of the bladder.
Microscopically the prostate consists of masses of long, slender, slightly branching glands, embedded in unstriped muscle and fibrous tissue; these glands open by delicate ducts (about twenty in number) into the prostatic urethra, which will be.
The penis is the intromittent organ of generation, and is made up of three cylinders of erectile tissue, covered by skin and subcutaneous tissue without fat.
In one of his letters home at this period he calls the campaign a "tissue of mismanagement, blunders, errors, ignorance and arrogance"; and outspoken criticism such as this brought him many bitter enemies throughout his career, who made the most of undeniable faults of character.
The muscular tissue of the dorsal body-wall is much reduced and the integument here is thin and FIG.
A, Of Chiton: f.t., fibrous tissue; a.b.v., afferent blood-vessel; e.b.v., efferent blood-vessel; g.l., laterally paired lamellae.
In the Gastropoda the muscular tissue of the buccal mass is coloured red by haemoglobin.
The third sub-family is that of the Microtinae, or voles, which are distributed all over Europe, Northern Asia and North America, and are characterized by the tympanic bulla of the skull being filled with honey-combed bony tissue, the small size of the infra-orbital foramen, and the deep pterygoid fossa on the palatal aspect.
The Octodontidae, which are exclusively South American, differ from the preceding family by the tympanic bulla being filled with cellular bony tissue, and by the par-occipital process curving beneath it, while the cheek-teeth are almost or completely rootless and composed of parallel plates.
It can also be extracted from almost all plants by treatment of the tissue with alcohol.
Aristotle's vague knowledge of the worm may have been derived from information acquired by the Greeks with Alexander the Great; but long before this time raw silk must have begun to be imported at Cos, where it was woven into a gauzy tissue, the famous Coa vestis, which revealed rather than clothed the form.
Within this muscular tube lies a parenchymatous tissue which may be uniform (Cestodes) or differentiated into a central or digestive, and a peripheral portion (some Turbellaria), or finally the central portion becomes tubular and forms the digestive sac (Trematodes), while the peripheral portion is separated from it by a space lined in some forms by a flattened epithelium (most Planarians).
In effect (6) it traces the Turbellaria to small two-layered organisms consisting of an outer ciliated epidermis and a central syncytial tissue.
From such beginnings the evolution of the Turbellaria leads first through the Acoelous forms in which the central syncytium is partly differentiated into digestive, muscular and skeletotrophic tissue, then to the more specialized Rhabdocoela, and so through the Alloeocoela to the Triclads and finally to the Polyclads.
The final arrest is due to paralysis of the respiratory centre in the medulla oblongata, hastened by a quasi-asthmatic contraction of the non-striped muscular tissue in the bronchial tubes, and by a "water-logging" of the lungs due to an increase in the amount of bronchial secretion.
The action is a direct one upon the muscular tissue (cf.
The typical heteromerous thallus shows on section a peripheral, thin and therefore transparent, layer, the cortical layer, and centrally a mass of denser tissue the so-called medullary layer, between these two layers is the algal zone or gonidial layer (figs.
According to the professed champions of that character, this conduct was a tissue of such dastardly imbecility, such heartless irresolution and such brainless inconsistency as for ever to dispose of her time-honoured claim to the credit of intelligence and courage.
Their functions in annual, biennial and herbaceous perennial plants cease after the ripening of the seed, whilst in plants of longer duration layer after layer of strong woody tissue is formed, which enables them to bear the strains which the weight of foliage and the exposure to wind entail.
The gardener aims usually at producing stout, robust, short-jointed stems, instead of long lanky growths defective in woody tissue.
In the case of the more delicate plants, the formation of roots is preceded by the production from the cambium of the cuttings of a succulent mass of tissue, the callus.
A large distinct leafy embryo lies in the middle of a dense, oily tissue (endosperm).
us to cases where the main mass of the sporophore forms a supporting tissue of closely crowded or interwoven hyphae, the sporogenous terminal parts of the hyphae being found at the periphery or apical regions only.
_ r, p, The sterile tissue from which jthe paraphyses h spring.
This is an extraordinarily large and varied group of forms which mostly live parasitically or saprophytically on vegetable tissue, but a few are parasitic on insect-larvae.
Some parasites attack many hosts and almost any tissue or organ (Botrytis cinerea), others are restricted to one family (Cystopus candidus) or genus (Phytophthora infestans) or even species (Pucciniastrum Padi), and it is customary to speak of rootparasites, leaf-parasites, &c., in expression of the fact that a given parasite occurs only on such organs - e.g.
3.1 Palisade Tissue and Spongy Cells 3.2 Cell Formations 3.3 Blade/Lamina and Stalk/Petiole 3.4 Venation
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.
Many tropical plants present on the upper surface of their leaves several layers of compressed cells beneath the epidermis which serve for storage of water and are known as aqueous tissue.
Bundles of fibro-vascular tissue.
2, m); they form the palisade tissue.
2, p), leaving air-spaces between them, which communicate with stomata; on this account the tissue has received the name of spongy.
These constitute a hypodermal layer, beneath which the chlorophyll cells of the parenchyma are densely packed together, and are elongated in a direction vertical to the surface of the leaf, forming the palisade tissue.
In some cases the cellular tissue is deficient at certain points, giving rise to distinct holes in the leaf, as in Monstera Adansonii.
The hardening of the extremities of the fibro-vascular tissue is the cause of the spiny margin of many leaves, such as the holly, of the sharp-pointed leaves of madder, and of mucronate leaves, or those having a blunt end with a hard projection in the centre.
By cultivation the cellular tissue is often much increased, giving rise to the curled leaves of greens, savoys, cresses, lettuce, &c.
It consists of the fibro-vascular bundles with a varying amount of cellular tissue.
20, p), forming the pulvinus, formed of cellular tissue, the cells of which exhibit the phenomenon of irritability.
Variations in the structure and forms of leaves and leafstalks are produced by the increased development of cellular tissue, by the abortion or degeneration of parts, by the multiplication or repetition of parts and by adhesion.
When cellular tissue is developed to a great extent, leaves become succulent and occasionally assume a crisp or curled appearance.
By a deficiency in development of parenchyma and an increase in the mechanical tissue, leaves are liable to become hardened and spinescent.
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.
The fall is directly caused by the formation of a layer of tissue across the base of the leaf-stalk; the cells of this layer separate from one another and the leaf remains attached only by the fibres of the veins until it becomes finally detached by the wind or frost.
These are collected in water, scraped over the edge of a shell to free them from adhering cellular tissue and epidermis, and more than once washed in a running stream, followed by renewed scraping till the desired purity of fibre is attained.
Within this is usually a sheath of connective tissue, which surrounds a layer of circular muscles; the latter may be split up into separate bundles, but more usually form a uniform sheet.
In the fibrils existing in the cell a sudden alteration of elasticity occurs, resulting in an increased tension on the points of attachment of the cell to the neighbouring elements of the tissue in which the cell is placed.
This is manifested by the muscular walls of the hollow viscera and of the heart, where it is the expression of a continuous liberation of energy in process in the muscular tissue, the outcome of the latter's own intrinsic life, and largely independent of any connexion with the nervous system.
In several of these it appears not unlikely that the recurrent explosive liberations of energy in the muscle tissue are not secondary to recurrent explosions in nerve cells, but are attributable to decompositions arising sua sponte in the chemical substances of the muscle cells themselves in the course of their living.
The effect of the fatigue substances upon the contraction of the tissue is manifest especially in the relaxation process.
This trophic influence which one neuron exerts upon others, or upon the cells of an extrinsic tissue, such as muscle, is exerted in that direction which is the one normally taken by the natural nerve impulses.
The nerve cells of the higher vertebrata, unlike their blood cells, their connective tissue cells, and even their muscle cells, early, and indeed in embryonic life, lose power of Nervous multiplication.
It has been suggested that the gradual cumulative result of the activity of the nerve cells during the waking day is to load the brain tissue with "fatigue-substances" Theories of which clog the action of the cells, and thus periodi cally produce that loss of consciousness, &c., which is sleep. Such a drugging of tissue by its own excreta is known in muscular fatigue, but the fact that the depth of sleep progressively increases for an hour and more after its onset prevents complete explanation of sleep on similar lines.
The secretion of mucus by the bronchi and trachea is greatly reduced and their muscular tissue is paralysed - a fact of which much use is made in practical medicine.
In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue, known as cambium; by the formation of a layer of cambium between the bundles (interfascicular cambium) a complete ring is formed, and a regular periodical increase in thickness results from it by the development of xylem on the inside and phloem on the outside.
In the smaller group, the Monocotyledons, the bundles are more numerous in the young stem and scattered through the ground tissue.
When placed on the stigma, under favourable circumstances, the pollen-grain puts forth a pollen-tube which grows down the tissue of the style to the ovary, and makes its way along the placenta, guided by projections or hairs, to the mouth of an ovule.
The nucellus is a cellular tissue enveloping one large cell, the embryo-sac or macrospore.
The endosperm-nucleus divides rapidly to produce a cellular tissue which fills up the interior of the rapidly-growing embryosac, and forms a tissue, known as endosperm, in which is stored a supply of nourishment for the use later on of the embryo.
In the natural order Rosaceae, the series Querciflorae, and the very anomalous genus Casuarina and others, instead of a single macrospore a more or less extensive sporogenous tissue is formed, but only one cell proceeds to the formation of a functional female cell.
If in its extension to contain the new formations within it the embryo-sac remains narrow, endosperm formation proceeds upon the lines of a cell-division, but in wide embryo-sacs the endosperm is first of all formed as a layer of naked cells around the wall of the sac, and only gradually acquires a pluricellular character, forming a tissue filling the sac. The function of the endosperm is primarily that of nourishing the embryo, and its basal position in the embryo-sac places it favourably for the absorption of food material entering the ovule.
Thus in Erythronium and Limnocharis the fertilized egg may form a mass of tissue on which several embryos are produced.
In Fucaceae and Laminariaceae the inner tissue is differentiated into a conducting system.
It is not difficult in such compact species to distinguish between superficial cells, whose chief function is assimilation, subjacent cells charged with reserve material, and a core of tissue engaged in the convection of elaborated material from part to part.
In all these cases, however, the end-cells of the filaments each give rise to a carpospore, and the aggregate of such sporiferous filaments is a cystocarp. Again, in the family of the Gelidiaceae, the single filament arising from the carpogonium grows back into the tissue and preys upon the cells of the axis and larger branches, after which the end-cells give rise to carpospores and a diffused cystocarp is formed.
Not even Riccia, with its rudimentary sporogonium, has so simple a corresponding stage as Bangia, for, while there is some amount of sterile tissue in Riccia, in Bangia the oospore completely divides to form carpospores.
It causes a local reaction with absorption of the scar tissue.
Like thiosinamine it has a specific action on scar tissue and has been used in urethral strictures.
The Jacobites surrounding James in Rome never ceased to weave at the endless tissue of their plot, but in Scotland nothing more substantial than the drinking of loyal healths was done, between the flight of Lockhart of Carnwath, the manager of the party, and the years of 1737-1744.
It is now known that similar internal secretions, or hormones, pass into the blood from every organ and tissue, so reaching and affecting every part of the body.
It abounds in error as to matters of fact, contradicts human experience, reason and morals, and is one tissue of folly, deceit, enthusiasm, selfishness and crime.
The effects of exposure in the case of white races are not only manifested by the acute attack of heat-stroke, but, if this is avoided by proper care, it is nevertheless certain that long residence in the Persian Gulf causes a certain amount of tissue degeneration, owing to the exposure of the body cells to abnormal conditions of temperature.
- In the skull there is a sagittal crest; the tympanic bulla is filled with cancellous tissue; the condyle of the lower jaw is rounded; and the premaxillae, or anterior bones of the upper jaw, have the full number of incisor teeth in the young state, the outermost of these being persistent through life as an isolated tooth.
It is employed for fire-works, for some descriptions of explosives, for safety matches and as an oxidizer in some operations, especially in dyeing and tissue printing.
BOLETUS, a well-marked genus of fungi (order Polyporeae), characterized by the central stem, the cap or pileus, the soft, fleshy tissue, and the vertical, closely-packed tubes or pores which cover the under surface of the pileus and are easily detachable.
A bubo is found to consist of a chain of enlarged glands, surrounded by a mass of engorged connective tissue, coagulated blood and serum.
The surrounding tissue is not engorged or oedematous.
The back of the body is occupied by a crest, called the dorsal fin, consisting of a hollow ridge, the cavity of which is divided into about 250 compartments or fin chambers, into each of which, with the exception of those near the anterior and posterior end of the body, projects a stout pillar composed of characteristic laminar tissue, the fin ray.
- As has already been indicated, a solid subcylindrical elastic rod, the notochord, surrounded by a sheath of laminar connective tissue, the cordal sheath, lies above the alimentary canal in contact with its dorsal wall, and extends beyond it both in front and behind to the obtusely pointed extremities of the body.
subcylindrical cord, also surrounded by a sheath of connective tissue.
This cord is neither elastic nor solid, but consists of nerve tissue, fibres and ganglion cells, surrounding a small central canal.
a book called Eikon Basilike, an elaborate tissue of invection against "the late king James."
Lars Johansson (1642-1674), who called himself "Lucidor the Unfortunate," has been the subject of a whole tissue of romance, most of which is fabulous.
Where there has been local mischief due to inflammation the dead leucocytes must be removed, and this is done either by their being converted into pus in one mass, and making their way through the tissues to the nearest surface, whether of skin or mucous membrane, from which it can be discharged, or they may undergo a process of fatty degeneration and absorption, leaving behind in some cases cheesy matter, in others hard connective tissue.
On the other hand, when the ulceration is old and the circulation through it poor, the aim of the therapeutist is to reawaken the normal reparative process, to bring about increased circulation and increased tissue change, and thereby insure healing.
One of the great difficulties in the way of applying this treatment is that in all probability many of the ferments or enzymes are altered during the process of absorption in the same way as the normal ferments of digestion, and unless the tissue enzymes can be isolated and injected subcutaneously the desired results will not be obtained.
During its continuance fat is absorbed from the subcutaneous tissue, and patients become very much thinner, so that it not only lessens flatulence, but reduces obesity.
Between A and B the loose cellular tissue of which the leaf is partly built up is seen in section, and at C the vertical palisade cells which give firmness to the upper surface of the leaf.
Amongst the loose tissue of the leaf numerous transparent threads are shown; these are the mycelial threads or spawn of the fungus; wherever they touch the leaf-cells they pierce or break down the tissue, and so set up decomposition, as indicated by the darker shading.
3, Section through diseased tissue showing dark masses of spores.
It was not until some time after his death that the enemies of his son first alleged that he was not of the family of La Scala, but was the son of Benedetto Bordone, an illuminator or schoolmaster of Verona; that he was educated at Padua, where he took the degree of M.D.; and that his story of his life and adventures before arriving at Agen was a tissue of fables.
w, bacterial tissue.
By means of microscopic examination more than one organism may sometimes be observed in the tissues,but one single organism by its constant presence and special relations to the tissue changes can usually be selected as the probable cause of the disease, and attempts towards its cultivation can then be made.
The tissues and fluids are treated by various histological methods, but, to speak generally, examination is made either in films smeared on thin cover-glasses and allowed to dry, or in thin sections cut by the microtome after suitable fixation and hardening of the tissue.
The injections are made by means of a hypodermic syringe into the subcutaneous tissue, into a vein, into one of the serous sacs, or more rarely into some special part of the body.
Not only are the general symptoms of poisoning in bacterial disease due to toxic substances, but also the tissue changes, many of them of inflammatory nature, in the neighbourhood of the bacteria.
In such diseases the bacteria, when introduced into the subcutaneous tissue, rapidly gain entrance to the blood stream and multiply freely in it, and by means of their toxins cause symptoms of general poisoning.
In this way secondary abscesses, secondary tubercle glanders and nodules, &c., result; in typhoid fever there is secondary invasion of the mesenteric glands, and clumps of bacilli are also found in internal organs, especially the spleen, though there may be little tissue change around them.
The effects produced by bacteria may be considered under the following heads: (I) tissue changes produced in the vicinity of the bacteria, either at the primary or secondary foci; (2) tissue changes produced at a distance by absorption of their toxins; (3) symptoms. The changes in the vicinity of bacteria are to be regarded partly as the direct result of the action of toxins on living cells, and partly as indicating a reaction on the part of the tissues.
(Many such changes are usually grouped together under the heading of " inflammation " of varying degree--acute, subacute and chronic.) Degeneration and death of cells, haemorrhages, serous and fibrinous exudations, leucocyte emigration, proliferation of connective tissue and other cells, may be mentioned as some of the fundamental changes.
A certain degree of non-specific immunity or increased tissue resistance may be produced locally, e.g.
Each rhopalium is a centre round which, as already stated, nervous tissue is concentrated.
Others cause much damage in forests, by boring under the bark and through the wood of trees, whilst some even burrow in the tissue of the leaves.
1) having a woody stock and herbaceous or woody branches, from the sides of which tendrils are produced which enable the branches to support themselves at little expenditure of tissue.
The function of the nodes is to raise again culms which have become bent down; they are composed of highly turgescent tissue, the cells of which elongate on the side next the earth when the culm is placed in a horizontal or oblique position, and thus raise the culm again to an erect position.
The tissue is often raised above the veins, form - - ?
The dark portions represent supporting and conducting tissue; the upper face bears furrows, at the bottom of each of which are seen the motor cells m.
The alkaloids are contained, according to Howard, chiefly in the cellular tissue next to the liber.
The head is about one-third of the length of the body, very massive, high and truncated in front; and owing its size and form mainly to the accumulation of a peculiarly modified form of fatty tissue in the large hollow on the upper surface of the skull.
Ovules naked, rarely without carpellary leaves, usually borne on carpophylls, which assume various forms. The single megaspore enclosed in the nucellus is filled with tissue (prothallus) before fertilization, and contains two or more archegonia, consisting usually of a large egg-cell and a small neck, rarely of an egg-cell only and no neck (Gnetum and Welwitschia).
The megaspore-nucleus divides repeatedly, and cells are produced from the peripheral region inwards, which eventually fill the sporecavity with a homogeneous tissue (prothallus); some of the superficial cells at the micropylar end of the megaspore increase in size and divide by a tangential wall into two, an upper cell which gives rise to the short two-celled neck of the archegonium, and a lower cell which develops into a large egg-cell.
This thread gives rise to a spiral ciliated band lying in a depression on the body of each spermatozoid; the large spermatozoids eventually escape from the pollen-tube, and are able to perform ciliary movements in the watery liquid which occurs between the thin papery remnant of nucellar tissue and the archegonial necks.
After the body of a spermatozoid has coalesced with the egg-nucleus the latter divides repeatedly and forms a mass of tissue which grows more vigorously in the lower part of the fertilized ovum, and extends upwards towards the apex of the ovum as a peripheral layer of parenchyma surrounding a central space.
By further growth this tissue gives rise to a proembryo, which consists, at the micropylar end, of a sac; the tissue at the chalazal end grows into a long and tangled suspensor, terminating in a mass of cells, which is eventually differentiated into a radicle, plumule and two cotyledons.
After the entrance of the pollengrain the pollen-chamber becomes roofed over by a blunt protuberance of nucellar tissue.
In a young cone the seminiferous scale appears as a hump of tissue at the base or in the axil of the carpellary scale, but Celakovsky, a strong supporter of the axillary-bud theory, attaches little or no importance to this kind of evidence, regarding the present manner of development as being merely an example of a short cut adopted in the course of evolution, and replacing the original production of a branch in the axil of each carpellary scale.
The megaspore becomes filled with tissue (prothallus), and from some of the superficial cells archegonia are produced, usually three to five in number, but in rare cases ten to twenty or even sixty may be present.
Similarly in the Araucarieae and in Widdringtonia the archegonia are numerous and scattered and often sunk in the prothallus tissue.
The tissue at the apex of the megaspore grows slightly above the level of the archegonia, so that the latter come to lie in a shallow depression.
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.
The megaspore is filled with tissue as in typical Gymnosperms, and from some of the superficial cells 3 to 5 archegonia are developed, characterized by long multicellular necks.
In Ephedra helvetica, as described by Jaccard, no proembryo or suspensor is formed; but the most vigorous fertilized egg, after undergoing several divisions, becomes attached to a tissue, termed the columella, which serves the purpose of a primary suspensor; the columella appears to be formed by the lignification of certain cells in the central region of the embryo-sac. At a later stage some of the cells in the upper (micropylar) end of the embryo divide and undergo considerable elongation, serving the purpose of a secondary suspensor.
Whilst very weak, its action is perfectly balanced throughout all nervous tissue, so much so that Sir Thomas Lauder Brunton has suggested its action to be due to its replacement of sodium chloride (common salt) in the fluids of the nervous system.
In Actinia, as in all Anthozoan zooids, the coelenteron is not a simple cavity, as in a Hydroid, but is divided by a number of radial folds or curtains of soft tissue into a corresponding number of radial chambers.
In common with all Coelenterate animals, the walls of the columnar body and also the tentacles and peristome of Actinia are composed of three layers of tissue.
When fully extended, the upper part of the zooid projects for some distance out of the calicle, and its wall is reflected for some distance over the lip of the latter, forming a fold of soft tissue extending to a greater or less distance over the theca, and containing in most cases a cavity continuous over the lip of the calicle with the coelenteron.
This fold of tissue is known as the edge-zone.
As growth proceeds, and parent and bud become separated farther from one another, the edge-zone forms a sheet of soft tissue, X 0 3 bridging over the space between the two, and resting upon projecting spines of the corallum.
This sheet of tissue is called the coenosarc. Its lower surface is clothed with a layer of calicoblasts which continue to secrete carbonate of lime, giving rise to a secondary deposit which more or less fills up the spaces between the individual coralla, and is distinguished as coenenchyme.
As the buds develop the canal system becomes much extended, and calcareous tissue is deposited between the network of canals, the confluent edgezones of mother zooid and bud forming a coenosarc. As the process continues a number of calicles are formed, imbedded in a spongy tissue in which the canals ramify, and it is impossible to say where the theca of one corallite ends and that of another begins.
After division the corallites continue to grow upwards, and their zooids may remain united by a bridge of soft tissue or coenosarc. But in some cases, as they grow farther apart, this continuity is broken, each corallite has its own edge-zone, and internal continuity is also broken by the formation of dissepiments within each calicle, all organic connexion between the two zooids being eventually lost.
The ear loses its starch, and ceases to grow, and its ovaries become penetrated with the white spongy tissue of the mycelium of the fungus which towards the end of the season forms the sclerotium, in which state the fungus lies dormant through the winter.
Some of these cells produced muscles and connective tissue; others absorbed and removed waste products, iron salts, calcium carbonate and the like, and so were ready to be utilized for the deposition of pigment or of skeletal substance.
Originally the calcareous substance of the plates (stereom) was pierced by irregular canals, more or less vertical, and containing strands of the soft tissue (stroma) that deposited the stereom, as well as spaces filled with fluid.
This consists of hard, elongated, slender, cylindrical or tapering, thread-like masses of epidermic tissue, each of which grows, without branching, from a short prominence, or papilla, sunk at the bottom of a pit, or follicle, in the true skin, or dermis.
Its function in the hairless Cetacea is discharged by the specially modified and thickened layer of fatty tissue beneath the skin known as " blubber."
Callosities, or bare patches covered with hardened and thickened epidermis, are found on the buttocks of many apes, the breast of camels, the inner side of the limbs of Equidae, the grasping under-surface of the tail of prehensile-tailed monkeys, opossums; &c. The greater part of the skin of the onehorned Asiatic rhinoceros is immensely thickened and stiffened by an increase of the tissue of both the skin and epidermis, constituting the well-known jointed " armour-plated " hide of those animals.
His whole life was a tissue of treachery.
In structure it is equally simple, being composed of parenchymatous tissue without any clearly marked conducting system.
9) consists of a more or less projecting neck and the venter, which is usually enclosed by the tissue of the prothallus.
The chlorophyll-containing tissue reaches the surface at the sides and base of the furrows, I.
In the cortical tissue beneatJI each furrow a wide intercellular space is present running the length of the internode, and called the (C, D, E from Strasburger's Lehrbuch der Bolanik, by permission of Gustav Fischer.) FIG.
The antheridia are deeply sunk in the tissue; the spermatozoids consist of a spiral of two or three coils, the numerous cilia being attached to the pointed anterior end.
The stem is monostelic, the protoxylem groups being towards the periphery of the xylem, the development of which is thus centripetal; the centre of the stele is occupied by sclerenchymatous tissue.
In the development of the sporangium the sporogenous tissue is derived from a number of superficial cells by divisions parallel to the surface.
The tapetum is derived from the layer of cells surrounding the sporogenous group. Short trabeculae of sterile tissue have been found to project into the cavity of the sporangium of some species.
All the saprophytic prothalli contain an endophytic fungus in definite layers of their tissue.
The sporogenous tissue, which is referable to several archesporial cells, is surrounded by a tapetum, mostly derived from the sporogenous group. In the microsporangium all the mother-cells undergo the tetrad division, giving rise to the numerous microspores.
The cavities of the large sporangia were sometimes traversed by trabeculae of sterile tissue resembling those found in Isoetes.
A meristematic zone forms a short distance outside the xylem, from which secondary tissue is developed both internally and externally; that to the inside contains both xylem and phloem elements.
In the young spike, which arises when the leaf is still very small, a band of tissue derived from superficial cells is distinguishable along either side; this sporangiogenic band gives rise to the sporogenous groups, the sterile septa between them, and the outer walls of the sporangia.
The sporangia themselves resemble those of Botrychium, which project from the ultimate subdivisions of the branched spike; each is developed from a number of cells, the sporogenous tissue arising from a single cell.
The stem, from the ground tissue of which sclerenchyma is absent, has a complicated system of steles arranged in concentric circles; the thick roots, the central cylinders of which have several alternating groups of xylem and phloem, arise in relation to these.
Enclosed within the sporocarp they can endure a period of drought, but on the return of moist conditions are extruded from the sporocarp by the swelling of a special mucilaginous tissue and the spores become free.
The development of the pfothalli is in general similar to that of the Salviniaceae, though the resemblance may be homoplastic. The stem in the less reduced forms is solenostelic with sclerenchymatous ground tissue occupying the centre of the stele.
On this view the origin of the sporophyte is looked for in the gradual development of sterile tissue in the generation arising from the fertilized ovum, and a consequent postponement of spore-formation.
Tracheae are essentially tubes like bloodvessels - apparently formed from the same tissue elements as bloodvessels - which contain air in place of blood, and usually communicate by definite orifices, the tracheal stigmata, with the atmosphere.
Chitin is not exclusively an ectodermal product, but occurs also in cartilaginous skeletal plates of mesoblastic origin (connective tissue).
They appear, in fact, to be an air-holding modification of the vasifactive connective tissue.
It seems that we have to suppose that the vasifactive tissue of Arthropoda can readily take the form of air-holding instead of blood-holding tubes, and that this somewhat startling change in its character has taken place independently in several instances - viz.
(h) The muscles of the body-wall and gut do not consist of transversely-striped muscular fibre, but of the unstriped tissue observed also in Chaetopoda.
(h) The muscles in all parts of the body consist of striped muscular fibre, never of unstriped muscular tissue.
Two or three layers of cells inside the epidermis constitute the tissue of the ovary, and overlie somewhat similar layers which form the coats of the seed.
The fine thread-like filaments composing the mycelium of the fungus are embedded in the tissue underneath and around the uredo-sorus, and draw from the host the nourishment required.
The muscular system is usually well developed, but there is deficiency of fatty tissue, which affects the features (particularly by giving relative prominence to the eyes) and the general character of the skin.
The argument, for instance, that intuitive and a priori beliefs gain their absolute character from the fact that they are the result of continued transmission and accumulation of past nervous modifications in the history of the race would, if taken seriously, lead us to the belief that ultimate ethical sanctions are to be sought, not by an appeal to the moral consciousness, but by the investigation of brain tissue and the relation of man's bodily organism to its environment.
Sir Leslie Stephen, for instance, wishes to substitute the conception of " social health " for that of universal happiness, and considers that the conditions of social health are to be discovered by an examination of the " social organism " or of " social tissue," the laws of which can be studied apart from those laws by which the individuals composing society regulate their conduct.
" The social evolution means the evolution of a strong social tissue; the best type is the type implied by the strongest tissue."
But on the important question as to what constitutes the strongest social tissue, or to what extent the analogy between society as at present constituted and organic life is really applicable, we are left without certain guidance.
His legend is a complex embroidery on a very ancient tissue.
==Therapeutics== Externally arsenious acid has been much used by quack doctors to destroy morbid growths, &c., a paste or solution being applied, strong enough to kill the mass of tissue and make it slough out quickly.
His reign was but a tissue of contradictions.
They possess two main rings of projecting tissue, and their extremities bear papillae irregularly arranged.
26, o), which is the lower portion enclosing the ovules destined to become seeds, and the stigma (g), a portion of loose cellular tissue, the receptive surface on which the pollen is deposited, which is either sessile on the apex of the ovary, as in the poppy, or is separated from it by a prolonged portion called the style (s) .
According to the development of veins and the growth of cellular tissue, petals present varieties similar to those of leaves.
In each a differentiation takes place in the layers beneath the epidermis, by which an outer layer of small-celled tissue surrounds an inner portion of large cells.
Those central cells are the mother-cells of the pollen, whilst the small-celled layer of tissue external to them becomes the endothecium, the exothecium being formed from the epidermal layer.
The ovules are attached to the placenta, which consists of a mass of cellular tissue, through which the nourishing vessels pass to the ovule.
102), and is traversed by a narrow canal, in which there are some loose projecting cells, a continuation of the placenta, constituting what is called conducting tissue, which ends in the stigma.
The stigma is the termination of the conducting tissue of the style, and is usually in direct communication with the placenta.
It consists of loose cellular tissue, and secretes a viscid matter which detains the pollen, and causes it to germinate.
- Vertical section of the ovule of the Austrian Pine (Pinus austriaca), showing the nucellus a, consisting of delicate cellular tissue containing deep in its substance an embryo-sac b.
This embryo-sac increases in size, gradually supplanting the cellular tissue of the nucellus until it is surrounded only by a thin layer of it; or it may actually extend at the apex beyond it, as in Phaseolus and Alsine media; or it may pass into the micropyle, as in Santalum.
112), through the conducting tissue of the style when present, and reach the interior of the ovary in angiosperms, and then pass to the micropyle of the ovule, one pollen-tube going to each ovule.
The ovary enlarges, and, with the seeds enclosed, constitutes the fruit, frequently incorporated with which are other parts of the flower, as receptacle, calyx, &c. In gymnosperms the pollen-tubes, having penetrated a certain distance down the tissue of the nucellus, are usually arrested in growth for a longer or shorter period, sometimes nearly a year.
Even the most delicate tissues, such as cambium and phloem, the endosperm of seeds, or the formative tissue of the growing-point, are frequently preserved cell for cell, both in calcareous and silicious material.
Here it need only be said that the masses of vegetable substance, more or less carbonized and chemically altered, of which coal is composed, frequently contain cells and fragments of tissue in a condition recognizable under the microscope, as for example spores (sometimes present in great quantities), elements of the wood, fibres of the bark, &c. These remnants, however, though interesting as revealing something of the sources of coal, are too fragmentary and imperfect to be of any botanical importance.
The tissue is made up of large, unseptate, occasionally branching tubes, with an undulating vertical course, among which much smaller tubes are irregularly interwoven.
Radially placed gaps in the tissue (at first erroneously interpreted as medullary rays, but subsequently more aptly compared to the air-spaces of large Algae) contain very sparse hyphae, which here branch more freely than elsewhere.
In Calamodendron (Upper Coal Measures) the wood has a more complex structure than in Calamites, the principal rays including radial tracts of fibrous tissue, in addition to the usual parenchyma.
The tissue thus formed often attained a considerable thickness.
The development of periderm was a constant feature, and this tissue attained a great thickness, consisting chiefly of a phelloderm, produced on the inner side of the formative layer, and no doubt subserving a mechanical function.
The word usage examples above have been gathered from various sources to reflect current and historial usage. They do not represent the opinions of YourDictionary.com.