Complete Text (Part 4)

opened oF the root has scarcely formed. 15. The ‘same, a little later, with the second joint lengthened. 12 GROWTH OF THE PLANT FROM THE SEED. [LESSON 3. they were so gorged and, as it were, misshapen, that they became quite unfitted to perform the office of foliage. This office is accordingly first performed by the succeeding pair of leaves, those of the plumule (Fig. 17, 18), which is put into rapid growth by the abundant nourishment contained in the large and thick seed-leaves. The latter, having fulfilled this office, soon wither and fall away. 29. This is carried a step farther in the Pea (Fig. 19, 20), a near relative of the Bean, and in the Oak (Fig. 21, 22), a near relative of the Beech. The differ- ence in these and many other similar cases is this. The cotyledons, which make up nearly the whole bulk of the seed are exces- sively thickened, so as to become nearly hemispherical in shape. They have lost all likeness to leaves, and all power of ever fulfilling the office of leaves. Ac- cordingly in germination they remain unchanged within the husk or coats of the seed, never growing themselves, but supplying abundant nourishment to the plumule (the bud for the forming stem) between them. This pushes forth from the seed, shoots upward, and gives rise FIG. 16, A Bean: the embryo, from which seed-coats have been removed: the smatt stem is seen above, bent down upon the edge of the thick cotyledons, 17, The same in early germination ; the plumule growing from between the two seed-leaves. 18. The germination more advanced, the two leaves of the plumule unfolded, and raised on a short joint of stem. FIG. 19. A Pea: the embryo, with the seed-coats taken off, 20. A Pea in germination. LESSON 3.] GROWTH OF THE PLANT FROM THE SEED. 18 to the first leaves that appear. In most cases of the sort, the radicle, or short original stemlet of the embryo be- low the cotyledons (which is plainly shown in the Pea, Fig. 19), lengthens very little, or not_at all; and so the cotyledons remain under ground, if the seed was covered by the soil, as every one knows to be the case with Peas. In these (Fig. 20), as also in the Oak (Fig. 22), the leaves of the first one or two joints are imperfect, and mere small scales; but genuine leaves immedi- ately follow. The Horsechestnut and Buck- eye (Fig. 23, 24) furnish another instance of the same sort. These trees are nearly related to the Maple ; but while the seed- leaves of the Maple show themselves to be leaves, even in the seed (as we have already seen), and when they germinate fulfil the office of ordinary leaves, those of the Buckeye and of the Horsechestnut (Fig. 23), would never be suspected to be the same organs. Yet they are so, only in another shape, — exceedingly thickened by the accumulation of a great quantity of starch and other nourishing matter in their substance ; and besides, their contigu- ous faces stick together more or less firmly, so that they never open. But the stalks of these seed-leaves grow, and, as they lengthen, push the radicle and the plumule ‘ out of the seed, when the former develops downwardly the roststhe’ latter upwardly the leafy stem and all it bears (Fig. 24). 30. Deposit of Food outside of the Embryo, Very often the nourish- ment provided for the seedling plantlet is laid up, not é the embryo itself, but around it. A good instance to begin with is furnished by the common Morning-Glory, or Convolvulus. ‘The embryo, taken out of the seed and straightened, is shown in Fig. 26. 1t consists of a short stemlet and of a pair of very thin and delicate green leaves, having no stock of nourishment in them for sustaining the FIG. 21. An acorn divided lengthwise. 22. The germinating Oak. 2 14 GROWTH OF THE PLANT FROM THE SEED. [LESSON 3. earliest growth. On cutting open the seed, however, we find this embryo (considerably crumpled or folded together, so as to occupy less space, Fig. 25) to be surround- ed by a mass of rich, mucilaginous matter (becoming rather hard and solid when dry), which forms the principal bulk of the seed. Upon this stock the embryo feeds in ger- mination ; the seed-leaves absorbing it into their tissue as it is rendered soluble (through certain chemical changes) and dissolved by the wa- ter which the germinating seed im- into a stem of consider ablelength, sd sformeasthe beginning of a root at its lower end, already imbedded in the soil (Fig. 27), the cotyledons now disengage themselves from the seed-coats, and ex- pand in the light as the first pair of leaves (Fig. 28). These immediately begin to elaborate, under the sun’s influence, what the root imbibes from the soil, and the new nourishment so produced is used, partly to increase the size of the little stem, root, bibes from the moist soil. Having by this aid 5 lengthened Z 2 its radicle pay and leaves already existing, and partly to TA] produce a second joint of stem with its A leaf (Fig. 29), then a third with its leaf a (Fig. 8) ; and so on. a 2 31. This maternal store of food, deposited in the seed along with the embryo (but not in its substance), the old botanists likened to FIG. 23. Buckeye: a seed divided. 94. A similar seed in gemination. FIG. 25. Seed and embryo of Mornmg-Glory, ent across, tached and straightened. 27. Germinating Morning-Glory. 28. Th Ms two thin seed-leaves expanded. ‘bryo of the same, dex same further advanced ; LESSON 3.] GROWTH OF THE PLANT FROM THE SEED. 15 the albumen, or white of the egg, which encloses the yolk, and therefore gave it the same name,— the albumen of the seed,—a name which it still retains. Food of this sort for the plant is also food for animals, or for man ; and it is this albumen, the floury part of the seed, which forms the principal bulk of such important grains as those of Indian Corn (Fig. 88-40), Wheat, Rice, Buck- wheat, and of the seed of Four-o’clock, (Fig. 86, 87), and the like. In all these last-named cases, it may be ob- served that the embryo is not enclosed in the albumen, but placed on one side of it, yet in close contact with it, so \ that the embryo may absorb readily from it the nourishment it requires when it begins to grow. Sometimes 2 the embryo is coiled around the outside, in the form of a ring, as in the Purslane and the Four-o’clock (Fig. 36, 37) ; sometimes it is coiled within the albumen, as in the Potato (Fig. 34, 85) ; some- times it is straight in the centre of the albumen, occupying nearly its % whole length, as in the Barberry (Fig. 32, 33), or much smaller and near one end, as in the Iris (Fig. 43) ; or some- times so minute, in the midst of the al- bumen, that it needs a magnifying-glass to find it, as in the But- EN FS 35 FIG. 29. Germination of the Morning Glory more advanced : the upper part only ; showing the leafy cotyledons, the second joint of stem with its leaf, and the third with its leaf just developing. FIG. 30. Section of a seed of a Peony, showing avery small embryo in the albumen, near one end, 31. This embryo detached, and more magnified. FIG, 32. Section of a seed of Barberry, showing the straight embryo in the middle of the albumen, 33, Its embryo detached. FIG. 34. Section o a Potato-seed, showing the embryo c embryo detached. FIG. 36. Section of the seed of Four-o'clock, showing the embryo coiled round the outside of the albumen. 37. Its embryo detached- led in the albumen, 35. Its 16 GROWTH OF THE PLANT FROM THE SEED. [LESSON 3, tercup or the Columbine, and in the Peony (Fig. 30, 81), where, however, it is large enough to be distinguished by the naked eye. Nothing is more curious than the various shapes and positions of the embryo in the seed, nor more inter ing than to watch its de- velopment in germination. One point is still to be noticed, since the botanist considers it of much importance, namely : — 32. The Kinds of Embryo as to the Number of Cotyledons, In all the figures, it is easy to see that the embryo, however various in shape, is constructed on one and the same plan ;— it consists of a radicle or stemlet, with a pair of cotyledons on its summit. Botanists there- fore call it dicotyledonous, — an inconveniently long word to express the fact that the embryo has two cotyledons or seed-leaves. In many cases (as in the Buttercup), the cotyledons are indeed so minute, that they are discerned only by the nick in the upper end of the little embryo; yet in germination they grow into a pair of seed-leaves, just as in other cases where they are plain to be seen, as leaves, in the seed. But in Indian Corn (Fig. 40), in Wheat, the Onion, the Iris (Fig. 43), &e., it is well known that only one leaf appears at first from the sprouting seed: in these the embryo has only one cotyle- don, and it is therefore termed by the botanists monocotyledo- 4 = nous ; — an extremely long word, like the other, of Greek derivation, which means one-cotyle- doned. The rudiments of one or more other leaves are, indeed, commonly present in this sort of embryo, as is plain to see in Indian Corn (Fig. 38 - 40), but they form a bud situated above or within the cotyledon, and enclosed by it more or less completely ; so tha. they evidently belong to the plumule (16); and these leaves appear in the seedling plantlet, each from within its predecessor, and there- fore originating higher up on the forming stem (Fig. 42, 44). This will readily be understood from the accompanying figures, with their explanation, which the student may without difficulty verify for him- FIG. 38. A grain of Indian Corn, flatwise, ett away a little, s0 as to show the embryo, ying on the albumen, which makes the principal bulk of the seed. FIG. 39, Another grain of Corn, cut through the iniddle in the opposite direction, divid- ing the embryo through its thick cotyledon and its plumule, the latter consisting of two leaves, one enclosing the other. FIG, 40, The embryo of Corn, taken out whole : the thick mass is the cotyledon ; the narrow body partly enclosed by it is the plumule ; the little projection at its base is the very ‘hort radicle enclosed in the sheathing base of the first leaf of the plumule. LESSON 3.] GROWTH OF THE PLANT FROM THE SEED. Ww self, and should do so, by examining grains of Indian Corn, soaked in water, before and also during germination. In the Onion, Lily, and the Iris (Fig. 43), the monocotyledonous embryo is simpler, consisting apparently of a simple oblong or cylindrical body, in which no distinction of parts is visible: the lower end is radicle, and from it grows the root; the rest is a cotyledon, which has wrapped up in it a minute plunule, or bud, that shows itself when the seeds sprout in germi- nation. ‘The first leaf which appears above ground in all these cases is not the cotyledon. In all seeds with one coty- ledon to the embryo, this remains in the seed, or at least its upper part, while its lengthening base_comes out, so as to extricate the plumule, which shoots upward, and de- velops the first leaves of the plantlet. These appear one above or within the other in sueces- sion, —as is shown in Fig. 42 and Fig. 44, —the first commonly in the form of a little scale or imperfect leaf; the second or third and the me following ones as the real, ordinary leaves of the plant. Meanwhile, from the root end of the embryo, a root (Fig. 41, 44), or soon a whole cluster of roots (Fig. 42), makes its appearance. 33. In Pines, and the like, the embryo con- sists of a radicle or stemlet, bearing on ats summit three or four, or often from five to * ten slender cotyledons, arranged in a circle (Fig. 45), and expanding at once into a circle of as many green leaves in germination (Fig. 46). Such embryos are said to be polycotyledonous. that is, as the word denotes, many- cotyledoned. 34. Plan of Vegetation, The student « who has understandingly followed the growth of the embryo in the seed into the seedling plantlet, — com- posed of a root, and a stem of two or three joints, each bearing a Fic. 41. FIG. 42. Grain of Indian Corn in germination. ‘The same, further advanced Qe 18 GROWTH OF THE PLANT FROM THE SEED. [LESSON 3, leaf, or a pair (rarely a circle) of Icaves, — will have gained a cor- rect idea of the plan of vegetation in general, and have laid a good foundation for a knowledge of the whole structure and physiology a of plants. For the plant goes on to grow in the same way throughout, by mere repetitions of what the early germinating plantlet displays to view,— of what was contained, in miniature or in rudiment, in the seed itself. So far as vegetation is concerned (leaving out of view, for the présent the flower and fruit), the full-grown leafy herb or tree, of whatever size, has nothing, and does nothing, which the seedling plantlet does not have and do. The whole mass of stem or trunk and foliage of the complete plant, even of the largest forest-tree, is composed of a succession or multiplication of similar parts, — one arising from the summit of another, — euch, so to say, the offspring of the preceding and the parent of the next. 35, In the same way that the earliest portions of the seedling stem, with the leaves they bear, are successively produced, so, joint by joint in direct succes- sion, a single, simple, leafy stem is developed and carried up. Of such a simple leafy stem many a plant consists (before flowering, at least), — many herbs, such as Sugar-Cane, Indian Corn, the Lily, the tall Banana, the Yucea, &c.; and among trees the “ Palms and the Cycas (wrongly called Sago Palm) exhibit the same simplicity, their stems, of whatever age, being unbranched columns ‘2 (Fig. 47). (Growth in diameter is of course to be considered, as well as growth in length. That, and the question how growth of any kind takes place, we will consider hereafter.) But more commonly, as soon as the plant has produced a main stem of a cer- tain length, and displayed a certain amount of foliage, it begins to FIG, 43, Section of a seed of the Iris, or Flower-de-Luce, showing its small embryo in the albumen, near the bottom. FIG. 44. Germinating plantlet of the Iris FIG, 45. Section of a seed of a Pine, with its embryo of several cotyledons. 46, Early seodling Pine, with its stenulot, displaying its six seed-leaves. LESSON 3.] GROWTH OF THE PLANT FROM THE SEED. 19 produce additional stems, that is, branches. The branching plant we will consider in the next Lesson. 36. ‘The subjoined figures (Fig. 47) give a view of some forms of simple-stemmed vegetation. The figure in the foreground on the left represents a Cycas (wrongly called in the conservatories Sago Palm). Behind it is a Yucca (called Spanish Bayonet at the South) and two Cocoanut Palm-trees. On the right is some Indian Corn, and bebind it a Banana. 20 GROWTH OF PLANTS FROM BUDS. \vesson 4. LESSON Iv. THE GROWTH OF PLANTS FROM BUDS AND BRANCHES, 37. We have seen how the plant grows so as to produce a root, and a simple stem with its foliage. Both the root and stem, how- ever, generally branch. 38. The branches of the root arise without any particular order. There is no telling beforehand from what part of a main root they will spring. But the branches of the stem, except in some extra- ordinary cases, regularly arise from a particular place, Branches or shoots in their undeveloped state are 39. Buds, These regularly appear in the axils of the leaves, — that is, in the angle formed by the leaf with the stem on the upper side; and as leaves are symmetrically arranged on the stem, the buds, and the branches into which the buds grow, necessarily par- take of this symmetry. 40. We do not confine the name of bud to the scaly winter-buds which are so conspicuous on most of our shrubs and trees in winter and spring. It belongs as well to the forming branch of any herb, at its first appearance in the axil of a leaf. In growing, buds lengthen into branches, just as the original stem did from the plumule of the embryo (16) when the seed germinated. Only, while the original stem is implanted in the ground by its root, the branch is implanted on the stem. Branches, therefore, are repetitions of the main stem. They consist of the same parts, — namely, joints of stem and leaves, —growing in the same way And in the axils of their leaves another crop of buds is naturally produced, giving rise to another generation of branches, which may in turn produce still another generation; and so on, — until the tiny and simple seedling develops into a tall and spreading herb or shrub; or into a massive tree, with its hundreds of annually increasing branches, and its thousands, perhaps millions,