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GROWTH OF PLANTS. 19
the starch is used up, in proportion to the growth, and the cell is again exhibited in its more simple form. In a transverse section of a young sprout near its exit from the tuber, about four different layers maybe distinguished—the cortical layer, next a layer of larger, then a layer of smaller, cells, and lastly, quite on the inside, a second layer of larger cells. Here we see nothing but regular structures; thick capsules of hexagonal form, and within them one or two nuclei (Fig. 1). Towards the cortex (corky layer) the cells are four-sided, and the farther one proceeds outwards, the natter do they become; still, nuclei may be distinctly recognised in them also. Wherever the so-called cells come in contact, a boundary line may be recognised between them; then comes the thick layer of cellulose, in which fine streaks may be observed; and in the interior of the capsular cavity you see a compound mass, in which a nucleus and nucleolus may be easily distinguished, and after the application of reagents the primordial utricle also makes its appearance as a complicated, wrinkled membrane. This is the perfect form of a vegetable cell. In the neighbouring cells lie a few larger, dimly lustrous, laminated bodies, the remains of starch (Fig. 7, c). The next object is of importance in my eyes, because I shall afterwards have to refer to it when instituting a comparison with new formations in animals. It is a longitudinal section of a young lilac bud, developed by the warm days we have had this month (February). In the bud a number of young leaves have already begun to develop themselves, each composed of numerous young cells. In these, the youngest parts, the external layers are composed of tolerably regular layers of cells, which have a rather flat, four-sided appearance, whilst in the internal layers the cells are more elongated, and in a few parts spiral vessels show themselves. Especially would I call your attention to the little outgrowths (leaf-hairs—Blatthaare), which protrude every
where along the border, and very much resemble certain animal excrescences, e. Jr., in the villi of the chorion, where they mark the spots at which young, secondary villi will shoot out. In our preparation, you see the little, clubPI0 8 shaped protuberances, which are
A B c repeated at certain intervals, and
'■'f HMkUfll are connected internally with
the rows of cells in the cambium. They are structures in which the more delicate forms of cells can best be distinguished, and, at the same time, the peculiar mode of growth be discovered. This growth is effected thus: a division takes place in some of the cells, and a transverse septum is formed; the newly-formed parts continue to grow as independent elements, and gradually increase in size. Not unfrequently divisions take place also longitudinally, so that the parts become thicker (Fig. 8, c). Every protuberance is therefore originally a single cell, which, by continual subdivision in a transverse direction (Fig. 8, a, b), pushes its divisions forwards, and then, when occasion offers, spreads out also in a lateral direction. In this way the hairs shoot out, and this is in general the
Fig. 8. Longitudinal section of a young February-shoot from the branch of a syringa. A. The cortical layer and cambium; beneath a layer of very flat cells are seen larger, four-sided, nucleated ones, from which, by successive transverse division, little hairs (a) shoot out, which grow longer and longer (4), and, by division in a longitudinal direction (c), thicker. B. The vascular layer, with spiral vessels. C. Simple, four-sided, oblong, cortical cells.—Growth of Plants.
GROWTH OF CARTILAGE.
mode of growth, not only in vegetables, but also in the physiological and pathological formations of the animal body.
In the following preparation—a piece of costal cartilage, in a state of morbid growth—changes are evident even to the naked eye, namely, little protuberances upon the surface of the cartilage. Corresponding to these the microscope shows a proliferation of cartilage-cells, and we find the same forms as in the vegetable cells; large groups of cellular elements, each of which has proceeded from a single previously existing cell, arranged in several rows, and differing from proliferating vegetable cells only in this—that there is intercellular substance between the individual groups. In the cells we can as before distinguish the external capsule, which, indeed, in the case of many cells, is composed of two, three, or more layers, and within them only does the real cell come with its membrane, contents, nucleus, and nucleolus.
In the following object you see the young ova of a frog, before the secretion of the yolk-granules has begun. The very large ovum (Eizelle) (Fig. 10, C) contains a nucleus likewise very large, in which a number of little vesicles are dispersed—and tolerably thick, opaque contents, beginning, at a certain spot, to become granular and brown. Around
Fig. 9. Proliferation of cartilage; from the costal cartilage of an adult. Large groups of cartilage-cells within a common envelope (wrongly so-called parent-cells), produced from single cells by successive subdivisions. At the edge, one of these groups has been cut through, and in it is seen a cartilagecell invested by a number of capsular layers (external secreted masses). 300 diameters.
the cell may be remarked the relatively thin, connective tissue of the Graafian vesicle, with a hardly visible layer of
epithelium. In the neighbourhood are lying several smaller
ova, which show the gradual progress of their
As a contrast to these gigantic cells, I place
before you an object from the bed-side; cells ^* lS|P from fresh catarrhal sputa. You see cells in
comparison very small, which, with a higher
Fig. 10. Young ova from the ovary of a frog. A. A very young ovum. B. A larger one. C. A still larger one, with commencing secretion of brown granules at one pole (e), and shrunken condition of the vitelline membrane from the imbibition of water, a. Membrane of the follicle. b. Vitelline 'membrane, c. Membrane of the nucleus. d. Nucleolus. S. Ovary. 150 diameters.
Fig. 11. Cells from fresh catarrhal sputa. A. Pus-corpuscles. a. Quite fresh, b. When treated with acetic acid. Within the membrane the contents have cleared up, and three little nuclei are seen. B. Mucus-corpuscles. a. A simple one. b. Containing pigment granules. 300 diameters.
LARGE AND SMALL ANIMAL CELLS. 23
power, prove to be of a perfectly globular shape, and, in which, after the addition of water and reagents, a membrane, nuclei, and, when fresh, cloudy contents can clearly be distinguished. Most of the small cells belong, according to the prevailing terminology, to the category of pus-corpuscles; the larger ones, which we may designate mucus-corpuscles or catarrhal cells, are partly filled with fat or greyish-black pigment, in the form of granules.
These structures, however small their size, possess all the typical peculiarities of the large ones; all the characters of a cell displayed by the large ones again present themselves in them. But this is, in my opinion, the most essential point—that, whether we compare large or small, pathological or physiological, cells, we always find this correspondence between them.