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enabled to withstand the tempest's shock. Vascular tissue is sometimes in the form of spiral fibre, which may be seen surrounding the pith of some plants, where the thread may easily be uncoiled.
11. Through the small tubular wood-cells the sap is carried from the roots to the leaves. Yet these cells, in the young and growing plant, have no openings, and the sap can pass from one to another only by making its way through their thin walls. And so short are the wood-cells generally, that, to rise a foot in such a tree as the basswood, the sap has to pass through the walls of about two thousand of these cells. There are no continuous11 veins, as many suppose, through which the sap of trees rises. Wood-cells in the bark are generally longer than in the central parts; they give great toughness to the inner bark of many plants, and they furnish the invaluable fibres of flax and hemp.
12. In addition to the cells which have been described, there are larger cells called ducts, which are either long single cells overlapping one another, or rows of cells placed end to end. Some of these are so large that they may be seen by the naked eye when cut across, but they are usually much too small for this. There are also, in various plants, canals or cavities formed between or among the cells, and filled with the particular products of the plant, such as milk, oil, turpentine, etc.
13. These various cells constitute the substance or framework of plants, from the mushroom of a night to the oak of centuries. The diversities of appearance which they present, when viewed by the aid of a microscope, enable us to distinguish one kind of vegetable growth from another, as the fibres of flax or linen from cotton, even when twisted and woven together, and thus to detect frauds in the manufacture
At 12 are represented portions of vascular tissue, showing the spiral arrangement of the fibres. At 13, a common arrangement of the wood-cells through which the sap circulates, placed end to end, or partially overlapping each other. At 14 is shown the appearance of fibres of flax, when viewed by the microscope; and at 12 15, the twisted appearance of
fibre of cotton.
of cloths, where the cheaper material of cotton is intermixed with linen. (Fig. 4.) Our obligations to the woody fibre of plants are infinite, for without it we should have neither linen nor cotton cloths, neither sails nor cordage for our ships, nor a door-mat upon which to clean our shoes; without it the books of the present day would have no existence, for the paper upon which they are printed is made of wooden fibre.
14. All plants have a covering called the cuticle; and this, formed of cells also, extends from the lowest root to the topmost twig, spreading over every leaf, and enveloping the whole plant. Yet in one of the great classes of plants, the exogenous, or outward-growing, this covering differs essentially from that of the endogenous, or inward-growing; for, while in the former it constitutes the true bark, which is separable from the wood, in the latter it is only a hardening of the outward portion of the stem. We shall hereafter see that this covering has offices to perform, especially in the leaves, quite similar to the functions of the human skin, which we have already described.
1 AD-HER'-ENT, united.
2 GERM, beginning; origin; first principle. 3 OM-NIS-CIENCE, universal knowledge.
IN MIN'-IA-TŪRE," on a very small scale.
5 MYR'-I-ADS, immense multitudes.
6 RIND, skin; bark, or outer coat.
7 MAZE, intricate winding.
8 "LUCID WEBS," the webs of life, well known to Him who wove them.
9 PROC'-ESS, pronounced pros'-ess.
10 Tis'-sûE (tish-shu), that which has the appearance of being woven.
11 CON-TIN'-U-OUS, separate; uninterrupted.
THE ROOTS OF PLANTS.
1. In what manner does the plant grow? and by what means is it nourished? are questions to be answered at the very outset1 of our inquiries2 into the physiology of vegetation. We are therefore next brought to consider those compound3 organs of plants which perform, among other functions, that of nutrition.
2. It is necessary to vegetable growth that certain substances should be absorbed, in a liquid state, through the roots, and that this nutritive liquid, or sap, should circulate through the stem to the leaves, which latter are the respiratory
or breathing organs, performing functions similar to the lungs of animals. From the leaves the sap is returned to the stem, after having been acted upon by the atmosphere, in a condition suitable for the formation of the new growth of the plant.
3. When the proper conditions of heat, light, and moisture allow the germination5 of the seed, which may be considered as a plant whose vital powers are dormant, its outer shell or covering bursts, and, in whatever position the seed is planted, the stem goes upward, while the The Root, 14that goes downward. rootlet invariably turns downward, and spreads out its little fibres to suck up nourishment from the earth.
4. In some rare instances roots may become branches, and branches act as roots. A maple-tree may be inverted," the branches being buried in the ground and the roots extended in the air, without killing the tree. The stems of some plants send out fibres which take root in the earth; and frequently twigs stuck in moist earth will take root and become large trees. Nearly two thousand years ago the Mantuan bard thus discoursed on this mode of propagation:
"These ways of planting Nature did ordain
For trees, and shrubs, and all the sylvan train.
"Some bow the vines; and, buried in the plain,
Even stumps of olives, bared of leaves, and dead,
It is probable that some allowance is to be made for the poet's privilege in Virgil's account of the dry poles; but it is not uncommon to see posts, set out for fences, growing as trees.
7. Although no solid substance can find its way through the roots into the plant, yet as the water which the rootlets absorb from the earth always contains earthy matters, it is through this medium that the plant is nourished, when the matter in solution is such as the plant requires for its structure.10 In this way, also, the plant is poisoned when substances injurious to it are thrown around the roots; and in the same way the wood of trees designed for ornamental purposes has been dyed by chemical substances.
8. Although roots generally grow in the ground, yet some, like those of parasites11 and air-plants, grow upon other vegetables, and have no immediate connection with the soil. Nor does it follow that all subterranean 12 vegetable organs are roots. The root-stalks of the sweet flag and ginger, aiso tubers like the common potato, artichoke, and dahlia, and the bulbs of the turnip, lily, tulip, and onion, may very properly be considered as underground stems, although, in botanical language, they are usually described as roots. (Fig. 6.)
Fig. 6.-Botanists not only give particular names to all parts of plants, but also particular terms to express their principal varieties of form. Hence, in advanced works on Botany, these terms must be defined and explained. Although, of the root, stem, and leaves, the former is the simplest, and least varied in its modifications, yet it exhibits quite a number of varieties in form, the principal of which will be described here.
At 1 is shown the sprouting of a grain or kernel of corn, sending upward a little stalk which contains a single seed-leaf, or co-tyl-e'-don, but has wrapped up in it other leaves. It has a single rootlet, or rad'-i-cle, which shoots downward. At 2 the corn plant is seen farther advanced, each leaf coming out from within the others as the plant grows. A cluster of fibrous or thread-like roots has also made its appearance.
At 3 is the seedling plant of the maple, with its pair of seed-leaves, or co-tyl-e'-dons, showing that it belongs to the class of di-co-tyl-e'-don-ous plants (see note, page 193). At 4 is a turnip-shaped or na'-pi-form root; 6, spindle-shaped, like a radish; 7, roots of the dählia, clustered and tuberous; 8, the potato, also tuberous; 9, the corm, or solid bulb of the crocus, which is merely a short and thick rootstock; 10, the scaly bulb of the lily; 11, the rhi-zo'-ma or rootstock of the Solomon's seal, properly an underground stem; 12, the strawberry, sending out runners, which take root and produce new plants.
9. Roots are classified, in respect to duration, as annual,13 biennial, and perennial. Annual roots are fibrous, 14 and produce, during their brief existence of a single season, herbage, flowers, and seeds. Biennial plants produce leaves the first year, but their flowers, fruit, and seeds appear during the second and last year of their existence. Perennial plants live through a series of years, producing leaves, flowers, and seeds during the natural period of their lives, which is sometimes reckoned by centuries.15
1 OUT'-SET, beginning.
2 IN-QUI'-RIES, questions; seeking for information.
9"MATTER IN SOLUTION," that which is dissolved in the water.
3 €ŎM'-POUND, not simple; composed of sev-11
5 GERM-I-NA'-TION, the act of sprouting.
6 DOR'-MANT, in a sleeping state.
10 STRUCT'-URE, growth or formation.
12 SUB-TER-RA'-NE-AN, being under the sur-
7 IN-VERT'-ED, turned upside down.
8 "MAN'-TU-AN BÄRD," Virgil: called the 14 FI'-BROUS, having small thread-like roots. Mantuan bard because he was born near 15 CEN'-TU-RIES, hundreds of years. Mantua, in Italy.
CHANGES PRODUCED BY CULTIVATION.
1. THE changes which roots and tubers can be made to undergo1 are numerous and highly beneficial to man. tato, for example, is a native of tropical America, and when found wild its tubers are small and scarcely fit to be eaten, while it has been rendered by cultivation one of the most valuable articles of food. The produce2 of an acre of wild potatoes could be held in a single measure, while the same area,3 under cultivation, will sometimes yield two or three hundred bushels. Cultivation has produced a thousand varieties of this tuber, varying in shape, size, color, and quality.
2. Beets, parsnips, and turnips are also made to assume many variations under proper cultivation. The bulb of the latter, for instance, has, since the beginning of the present century, been changed from globular to spindle-shaped, in colors from white and yellow to purple and green, and in weight from a couple of ounces to twenty pounds. So also with the carrot, which in a wild state is a slender, tapering root of a yellowish-white color, but which, by cultivation, increases in