Parenchyma Sentence Examples
This passes gradually into the thinner-walled parenchyma of the inner cortex.
Distinctive yellow spots can be seen as a result of dead palisade parenchyma cells.
The sieve-tubes differ, however, from the tracheids in being immediately associated, apparently constantly, not with starchy parenchyma, but with parenchymatous cells, containing particularly abundant proteid contents, which seem to have a function intimately connected with the conducting function of the sieve-tubes, and which we may call proteid-cells.
Associated with it are other tissues, consisting of parenchyma, mainly starchy, and in the Phanerogams particularly, of special stereom.
The sieve-tubes, with their accompanying parenchyma or stereom, constitute the tissue called phloem.Advertisement
When there is a single protoxylem strand in the centre of the stele, or when, as is more commonly the case, there are several protoxylem strands situated at the internal limit of the xylem,, the centre of the stem being occupied by parenchyma, the stele is endarch.
As a bundle is traced towards its blind termination in the mesophyll the peridesmic stereom first disappears, the sieve-tubes of the phloem are replaced by narrow elongated parenchyma cells, which soon die out, and the bundle ends with a strand of tracheids covered by the phloeotermic sheath.
Sometimes all the parenchyma within the stele undergoes this change.
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.
When a given initial cell of the cambium has once begun to produce cells of this sort it continues the process, so that a radial plate of parenchyma cells is formed stretching in one plane through the xylem and phloem.Advertisement
The xylem and phloem parenchyma consist of living cells, fundamentally similar in most respects to the medullary ray cells, which sometimes replace them altogether.
The parenchyma is often arranged in tangential bands between the layers of sievetubes and tracheal elements.
The xylem parenchyma is often found in strands associated with the tracheal elements.
The fibres belong to the same n,orpholcgical category as the parenchyma, various transitions being found between them; thus there may be thin-walled cells of the shape of fibres, or ordinary fibres may be divided into a number of superposed cells.
These intermediate cells, like the ordinary parenchyma, frequently store starch, and the fibres themselves, though usually dead, sometimes retain their protoplasm, and in that case may also be used for starch accumulations.Advertisement
They are nearly always aggregated in strands, which, like those of the parenchyma, are not isolated, but are connected with one another.
In the secondary tissues of Dicotyledons we may have, as already described, considerably more differentiation of the cells, all the varieties being referable, however, on the one hand to the tracheal or sieve-tube type, on the other to the parenchyma type.
The formation of additional cambial cylinders or bands occurs in the most various families of Dicotyledons and in some Gymnosperms. They may arise in the pericycle or endocycle of the stele, in the cortex of the stem, or in the parenchyma of the secondary xylem or phloem.
An ordinary cambium is scarcely ever found in the Monocotyledons, but in certain woody forms a secondary meristem is formed outside the primary bundles, and gives rise externally to a little secondary cortex, and internally to a secondary parenchyma in which are developed numerous zones of additional bundles, usually of concentric structure, with phloem surrounded by xylem.
Opposite the primary xylems, the cambium either (a) forms parenchyma on both sides, making a broad, secondary (principal) ray, which interrupts the vascular ring and is divided at its inner extremity by the islet of primary xylem; or (b) forms secondary xylem and phloem in the ordinary way, completing the vascular ring.Advertisement
The internal tissue formed by the phellogen is known as phelloderm, and consists usually of ordinary parenchyma.
Eventually the new phellogens reach the level of the secondary phloem, and are formed in the parenchyma of the latter, keeping pace in their inward march with the formation of fresh secondary phloem by the cambium.
This has a relatively large development of succulent parenchyma on its upper and lower sides.
Companion cells are not found in the Pteridophyta and Gymnosperms. In the latter their place is taken by certain cells of the medullary rays and bast parenchyma.
Metanemertini, in which the nervous system lies inside the dermal muscles in the parenchyma; the mouth lies in front of the level of the brain; the proboscis as a ru'e bears stylets; the intestine nearly always has a caecum.Advertisement
These cells are f - - imbedded in the peri pheral parenchyma, E"- and lead into convo luted excretory tubes _ that form an anasto- - mosis opening to the exterior by a pore at the " hinder " end of the body.
The parenchyma is made up of stellate cells the processes of which formareticulum.
A well-developed cellular parenchyma forms a matrix in which the muscular, excretory and generative organs are imbedded.
The excretory tubes, the nervous system, and the parenchyma and integument are continuous from one end of the worm to the other.
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.
In leaves having a very firm texture, as those of Coniferae and Cycadaceae, the cells of the parenchyma immediately beneath the epidermis are very much thickened and elongated in a direction parallel to the surface of the leaf, so as to be fibre-like.
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 skeleton leaves, or leaves in which the parenchyma is removed, this arrangement is well seen.
In some leaves, as in the barberry, the veins are hardened, producing spines without any parenchyma.
In some cases there is only a network of filament-like cells, the spaces between which are not filled with parenchyma, giving a skeleton appearance to the leaf, as in Ouvirandra fenestralis (Lattice plant).
In both simple and compound leaves, according to the amount of segmentation and the mode of development of the parenchyma and direction of the fibro-vascular bundles, many forms are produced.
When the development of parenchyma is such that it more than fills up the spaces between the veins, the margins become wavy, crisp or undulated, as in Rumex crispus and Rheum undulatum.
By a deficiency in development of parenchyma and an increase in the mechanical tissue, leaves are liable to become hardened and spinescent.
Characeae are separated from other Chlorophyceae by Ulvaceae that there is any pretension to the formation of a true a long interval, and present the highest degree of differentiation of parenchyma within the limits of the Chlorophyceae.
In Coleochaetaceae the branches are often welded into nexion with each whorl there arise, singly or in pairs, branches which a plate, simulating a parenchyma.
It is held that in Coleochaete a parenchyma results from the division of the oospore, from each cell of which a zoospore arises.
In Fucaceae, Dictyotacea, and in Laminariaceae and Sphacelariaceae, among Phaeosporeae, the thallus consists of a true parenchyma; elsewhere it consists of free filaments, or filaments so compacted together, as in Cutleriaceae and Desmarestiaceae, as to form a false parenchyma.
In such cases as Lemanea, the terminal cells of the lateral branches form a superficial layer which has all the appearance of a parenchyma when viewed from the surface.
A,a,Female Heterodera schachtii Schmidt, breaking through the epidermis of a root; the head is still embedded in the parenchyma of the root.
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.
The protoxylem-elements are situated at the extreme inner edge of the secondary wood, and may occur as small groups of narrow, spirallypitted elements scattered among the parenchyma which abuts on the main mass of wood.
The genus Pinus serves as an illustration of wood of a distinct type characterized by the absence of xylemparenchyma, except such as is associated with the numerous resincanals that occur abundantly in the wood, cortex and medullary rays; the medullary rays are composed of parenchyma and of horizontal tracheids with irregular ingrowths from their walls.
In the Abietineae the phloem consists of parenchyma and sieve-tubes only, but in most other forms tangential rows of fibres occur in regular alternation with the parenchyma and sieve-tubes.
One form of Cephalotaxus is characterized by the presence of short tracheids in the pith, in shape like ordinary parenchyma, but in the possession of bordered pits and lignified walls agreeing with ordinary xylem-tracheids; it is probable that these short tracheids serve as reservoirs for storing rather than for conducting water.
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.
Abies, Tsuga, Larix, &c., the mesophyll is heterogeneous, consisting of palisade and spongy parenchyma.
The secondary wood of Ephedra consists of tracheids, vessels and parenchyma; the vessels are characterized by their wide lumen and by the large simple or slightly-bordered pits on their oblique end-walls.
In Gnetum Gnemon, as described by Lotsy, a mature embryo-sac contains in the upper part a large central vacuole and a peripheral layer of protoplasm, including several nuclei, which take the place of the archegonia of Ephedra; the lower part of the embryo-sac, separated from the upper by a constriction, is full of parenchyma.
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 male sporophylls are similar in form to the vegetative leaves, but smaller; sunk in their parenchyma are numerous tubular loculi, containing large pollen-grains, which are pluricellular like those of Cordaites; the female fructification had not yet been identified with certainty.
Initially examine under low power (x10) to identify areas of normal liver parenchyma, and the areas of granulomatous inflammation.
The section shows from the pith (at right) to the cortical parenchyma (at left ).
The lesion displays heterogeneous texture with echogenicity similar to the normal renal parenchyma.
This involves placement of an expandable metallic stent between the branches of the portal vein and systemic circulation within the liver parenchyma.
In contrast, these receptors were not detected on mast cells purified from human lung parenchyma.
The right kidney parenchyma was thinned and irregular and contained low attenuation areas and tiny foci of calcification.
Associated with the conducting parenchyma are frequently found hydroids identical in character with those of the central strand of the stem, and no doubt serving to conduct water to or from the leaf according as the latter is acting as a transpiring or a waterabsorbing organ.
Frequently, also, a considerable differentiation of vegetative tissue occurs in the wall of the spore-capsule itself, and in some of the higher forms a special assimilating and transpiring organ situated just below the capsule at the top of the seta, with a richly lacunar chlorophyllous parenchyma and stomata like those of the wall of the capsule in the Anthocerotean liverworts.
The xylem parenchyma cells are connected, as are the medullary ray cells, with the tracheal elements by one-sided bordered pitsi.e.
In the simplest condition we have merely tracheae and sieve-tubes, respectively associated with parenchyma, which in the former case is usually amylom, i.e.
In these we have (1) the evaporation from the damp delicate cell-walls into the intercellular spaces; (2) the imbibition by the cell-wall of water from the vacuole; (3) osmotic action, consequent upon the subsequent increased concentration of the cell sap, drawing water from the wood cells or vessels which abut upon the leaf parenchyma.
The term parenchyma is applied to tissues whose cells are isodiametric or cylin.drical in shape, prosenchyma tissues consisting of long narrow cells, with pointed ends.
It always consists of true parenchyma, and is entirely formed by the cutting off of segments from an apical cell.
The whole of the cortex, stereom and parenchyma alike, is commonly living, and its cells often contain starch.
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.
In other cases it does not differ histologically from the parenchyma of the rest of the cortex, though it is often distinguished by containing particularly abundant starch, in which case it is known as a starch sheath.
By the formation of numerous cross-walls the resemblance to parenchyma is increased.