Parenchyma

“ Fig. 19. Wood fiber proper has much thickened lignified walls and no pits, and its main function is mechanical support. Fibrous cells are like the wood fibers except that they retain their protoplasm. Parenchyma is composed of vertical groups of short cells, the end ones of each group tapering to a point, and each group originates from the transverse division of one cambium cell. They are commonly grouped around the vessels (tracheæ) . Parenchyma constitutes the pith rays and other similar fibers, retains its protoplasm, and becomes filled with starch in autumn. ”

“ When a cambium cell passes over into wood-parenchyma it first undergoes a few horizontal divisions transverse to its long axis, and then we have a vertical row of five or six parenchymatous cells, the walls of which do not thicken much, but obtain small simple pits, and retain part of their living contents—protoplasm, nucleus, starch-forming corpuscles, etc.—and indeed present much resemblance to the cells of the medullary rays themselves. ”

“ This passes gradually into the thinner-walled parenchyma of the inner cortex. The whole of the cortex, stereom and parenchyma alike, is commonly living, and its cells often contain starch. The centre of the stem in the forms living on soil is occupied by a strand of narrow elongated hydroids, which differ from those of the liverworts in being thin-walled, unlignified, and very seldom pitted (fig. 1, J) . The hydrom strand has in most cases no connexion with the leaves, but runs straight up the stem and spreads out below the sexual organs or the foot of the sporogonium. ”

“ Collenchyma cells differ from parenchyma cells in a number of ways: first, the cell cavity is smaller; secondly, the walls are thicker, the greater amount of thickening being at the angles of the cells—that is, the part of the cell wall which is opposite the usual intercellular space of parenchyma cells, while the wall common to two adjoining cells usually remains unthickened. In horehound stem (Plate 30, Fig. 2) the thickening is so great at the angles that no intercellular space remains. ”

“ In later years the length of the cambial cells increases, and hence the length of the elements in the wood.
The phloëm or bast of the individual bundle is separated from its neighbors by large rays of parenchyma, the cells of which agree with the secondary bast-parenchyma rays. As these pass into the cortex they widen, as they do at the pith (Fig. 12) .
The oldest portion of the phloëm—that next the cortex—consists of a group of thick-walled bast fibers with their lumina nearly obliterated; these are long, spindle-shaped fibers much like the fibers of the wood. ”

“ Thus we see the Pith, which is often tough, in many Roots, as Parsneps, Turneps, &c. is tender and edible. So here, the Parenchyma, though originally no more than the Barque, yet the plenty and purity of its Sap being likewise effectual to the fulness and fineness of its growth, it thus becomes a soft and tender meat. The Branchery is [151] nothing else but the Ramifications of the Lignous Body throughout all the parts of the Parenchyma; the greater Branches being likewise by the Inosculations of the less (as in the Leaf) united together. The main Branches are usually fifteen ”

“ The ordinary epidermal cells have thick outer walls and thin inner walls. Beneath many of the epidermal cells are large air-spaces.
Upper Palisade Parenchyma. The palisade parenchyma vary from four to five layers. The inner palisade cells are shorter and broader than the outer layer of cells.
Parenchyma. The parenchyma cells (Fig. 4) are rounded in form and they are arranged in the form of columns which are one cell in thickness above, but two to three cells in thickness near the under epidermis. Between each chain of cells is a larger intercellular space (Fig. 6) . ”

“ Each organ has as yet only its nutritive parenchyma, the parenchyma upon which nature has imprinted the form of the organ, that is to be developed there. In proportion as this outline is increased, the nutritive substances penetrate it, and then each organ, which until that time had been like the rest in its nature, and forming with them a homogeneous mass, begins to be distinct, and have a separate existence; each one draws from the blood the substance that is proper for it. This addition gives the attributes of thickness, of density, and of nature ”

“ The fibro-vascular bundles from the stem bend out into the leaf, and are there arranged in a definite manner. 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. 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. ”

“ The dermo-muscular layer consists of annular, longitudinal, and even diagonal fibres, while the parenchyma is traversed by dorso-ventral fibres.
The central NERVOUS SYSTEM, which is embedded in the parenchyma of the body, consists of cerebral ganglia, united together in the shape of dumb-bells, and of two or more longitudinal MEDULLARY FASCICLES, often forming transverse anastomoses. Organs of sense usually occur only in the free-living species, more rarely during the free-living stages of a few parasitic species and in a few ectoparasitic forms. ”

“ An outgoing branch, as seen in a tangential section of a stem, consists of a parenchymatous pith surrounded by a ring of vascular bundles, in which the characteristic carinal canals have not yet been formed, but if the section has cut the branch further from its base, there may be seen a circle of irregular gaps marking the position of the carinal canals. Such gaps are often occupied by thin parenchyma, and contain protoxylem elements. ”

“ There are also thick-walled bast fibres (Fig. 82) in the bast that serve for support. (3) There is also some parenchyma in the new bast; it is now in part a storage tissue. Sometimes [67] the walls of parenchyma cells in the cortex thicken at the corners and form brace cells (Fig. 83) (collenchyma) for support; sometimes the whole wall is thickened, forming grit cells or stone cells (Fig. 84; examples in tough parts of pear, or in stone of fruits) . ”

“ From the peripheral steles, or from the more external bands of the vascular network, roots are given off which pass in a sinuous vertical course through the cortex, appearing on the surface between the leaf-bases. In older stems, after leaf-fall, the tissue immediately external to the vascular region produces secondary parenchyma with which the roots become intimately associated by their outermost cells. ”

“ The walls of the organ are composed almost entirely of a soft, tender parenchyma, formed, for the most part, of vascular ramifications, the trunks of which, three or four in number, communicate with the interior of the branchial heart, through the peduncle. The walls of these trunks and of the peduncle are composed of stout, tough membrane. The cavity of the appendage does not communicate with that of the heart, but opens, as we have seen, externally, or into the chamber within which the organ is placed, so that the fluid surrounding it will bathe its inner as well as its outer surface. ”

“ Occasionally, gestation, parturition, the puerperium, and lactation seem to exercise a favorable influence on the state of the parenchyma. In exceptional cases all traces of the original chronic metritis disappear with the puerperium. The connective-tissue hyperplasia may undergo the same involution to which the hypertrophied muscular tissue is subject. This favorable termination of the disease is seldom observed during the stage of induration. ”

“ Clearly the like must happen if the liquid is to be drawn out of a tissue which cannot either diminish in bulk bodily or allow its components individually to diminish in bulk. In an ordinary leaf, the upper layer of parenchyma, formed as it is of closely-packed cells that are without interspaces, and are everywhere held fast within their framework of veins, can neither contract easily as a mass, nor allow its separate cells to do so. ”

“ For the bones, it is phosphate of lime and gelatine; it is gelatine alone for the cartilages, tendons, &c.; fibrin for the muscles, albumen for certain other organs; so that if the nutritive parenchyma of a bone was filled with fibrin, it would be a muscle in the form of a bone, and vice versa, a muscle would become a bone with a muscular form, if its parenchyma was filled up with earthy and gelatinous substances. We should know the nature of all the living parts, if their nutritive substances were known to us ”

“ The parenchyma of the body itself exhibits a well-marked [Pg 471] distinction in the majority of instances into a cortical and medullary substance. The cortical substance is formed of rather irregular columnar cells, for the most part one row deep, arranged round the periphery of the body. Its cells measure on about an average .03 Mm. in their longest diameter. The medullary substance is more or less distinctly divided into alveoli, and is formed of irregularly polygonal cells ”

“ Parenchyma.—Each of these glands is provided with a teat containing a large sinus. Anatomically the mamma consists of glandular tissue arranged like a bunch of grapes, in which the active tissues of the acini deliver their secretion into little excretory canals, which unite, forming a large collecting plexus. The collecting canals, or galactophorous canals, open into the galactophorous sinus, which occupies the entire depth of the teat and communicates with the exterior by a small pore provided with a sphincter. ”

“ As examples the stems of Panicum flavidum, Panicum colonum, Panicum Crus-galli and Panicum fluitans may be considered. The stem of Panicum flavidum is broadly ovate in cross section with a flat front and is more or less solid, though occasionally the parenchymatous cells in the centre get broken. Two rows of vascular bundles surround a fairly large amount of parenchymatous cells of the ground tissue. There is a continuous ring of sclerenchyma separated from the epidermis by a fairly broad cortex. The cortex has a number of fairly large air-cavities separated by bands of parenchymatous cells. ”

“ Gray's 220th article gives the following account. "It is not a distinct substance, but a layer of delicate new cells full of sap. The inner portion of the cambium layer is, therefore, nascent wood, and the outer nascent bark. As the cells of this layer multiply, the greater number lengthen vertically into prosenchyma, or woody tissue, while some are transformed into ducts" (wood vessels?) "and others remaining as parenchyma, continue the medullary rays, or commence new ones." ”

“ Whilst all inorganic bodies increase by the addition of particles, there is here at first an expansive force, from which length and breadth arise, afterwards substances are exhaled into the parenchyma, which lengthen and widen it. ”

“ The tissue-elements just described are found only in the more complicated secondary vascular tissues of certain Dicotyledons. A considerable evolution in complexity can be traced in passing from the simplest forms of xylem and phloem found in the primary vascular tissues both among Pteridophytes and Phanerogams to these highly differentiated types. 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. consists of starch-containing cells, and in the latter of proteid cells. ”

“ The fibres belong to the same morphological 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. ”

“ There is, again, no reason why the phagocytic cells should not continue to perform their scavenger function until such time as the degenerative process in the parenchyma (a process not necessarily progressive in the absence of the spirochete or its products) ceases. ”

“ 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. ”

“ I cannot better this earlier statement, which in beginning 'Proserpina,' I intended to form a part of that work; but, as readers already in possession of it in the original form, ought not to be burdened with its repetition, I shall republish those chapters as a supplement, which I trust may be soon issued.
[46] "'Diachyma' is parenchyma in the middle of a leaf!" (Balfour, Art. 137.) Henceforward, if I ever make botanical quotations, I shall always call parenchyma, By-tis; prosenchyma, To-tis ”

“ Frequently on the epidermis may be remarked a delicate network of the cells constituting the fruit pulp (p) . Beneath the epidermis lies a very delicate transverse cellular layer (qu) followed by the parenchyma, as already stated. The remaining elementary forms are not readily observed on a plane surface but only in section, though we adjoin a few diagrams, showing the layers as isolated from the pericarp; namely, fig. 9 parenchyma, a layer of sklerogenous cells, fig. 10, and the silver membrane (is) with two superjacent Mitscherlich particles (tr) in fig. 11.80
Fig. ”