Page:The American Cyclopædia (1879) Volume XIII.djvu/592

 576 PLANT separation of flowering plants into two great classes. In the conifers and some other plants the cotyledons often appear to be more than two, but these polycotyledonous embryos are regarded as dicotyledonous with the cotyledons subdivided. To return to the bean. Even in the very rudimentary state to which we have traced it, the bean just " up," as in the com- mon expression, has all the organs of vegeta- tion that it needs, all in kind that it ever will have, and indeed all that any plant has. Root, stem, and leaf, being all that are con- cerned in the growth of the plant, its increase in size, are termed the organs of vegetation ; the two last named already existed in the seed, while the root was formed as soon as germination was fairly accomplished. The fu- ture growth of the plant consists in the repe- tition of these organs, and though in different plants these are wonderfully varied in form and size, and are sometimes turned aside from their proper functions, they may all be traced to these three elementary organs. In the plu- mule there is provision for the upward growth of the plant, though in a remarkable African genus, Welwitscliia, no upward growth takes place, the long and leathery cotyledons being all the foliage that the plant, though supposed to live upward of a century, ever produces. In all plants the leaf or leaves are produced upon the stem at a point called the node ; the space between one node and the next is the ^internode ; the plant then, no matter how long bearing nodes separated by internodes in fact, is merely a repetition of the embryo, which was a very short stem or internode with a pair of leaves. In the plumule the undevel- oped leaves were upon very short undeveloped internodes, and as growth went on these in- ternodes elongated, and grew from nourish- ment afforded by the cotyledons at first, and afterward from that primarily taken up by the root. The plumule is a very simple bud, but whether of this character or more highly or- ganized, a bud (leaf bud) always consists of un- developed leaves upon very short internodes ; as the bean plant elongates there is still found at its upper end a simple bud, or what gar- deners call the " growing point." The Root. This may exist but a single season (annual), it may last for two seasons (biennial), or con- tinue indefinitely (perennial). In a general way its functions are to absorb from the soil water and whatever it may hold in solution, and it also serves to fix the plant firmly to the earth. Its manner of growth will be men- tioned further on ; its chief office being that of absorption, it generally exposes the largest possible surface ; in annual plants, where the work is to be done quickly, it is usually much subdivided and presents a mass of threads (fibrous), and these, and young roots gener- ally, have their surface greatly increased by means of root hairs, which are prolongations like minute tubes, so small as to require a mag- nifier to see them, but which in the aggre- gate present an immense surface. If a main root descends into the soil, throwing off small branches from its sides, it is called the tap root; but its identity is often lost by its di- viding into numerous small branches. These branches may be thickened at intervals (a no- dose root), as in the dropwort, or be entirely fleshy, as in the tuberous root of the dah- lia. In some plants, especially biennials, the root, besides performing the usual functions, is converted into a storehouse for food; the roots of agriculture, the beet, carrot, tur- nip, and others, afford illustrations of this. The first year of these plants is passed in ac- cumulating nutriment in the root, which be- comes very much enlarged in diameter ; but if such roots are examined while growing, they will be found abundantly supplied with root- lets or small branches, to carry on the proper work of absorption. If a hardy root of this kind, like the parsnip, be left in the ground over winter, or a tender one, like the beet, be set out the next spring, the growth from them is very rapid; a strong stalk is thrown up, flowers and seed are produced, and this main- ly at the expense of the food contained in the fleshy root ; and it is well known that when this second growth has fairly started the roots become exhausted of their nutriment and use- less as food for man or beast. Boots, whether one or several, which start from the lower end of the radicle, are primary roots ; those which are produced elsewhere are secondary ; many stems which trail along the ground (as squash and sweet potato) throw out secondary roots, and the propagation of plants by layering and from cuttings depends upon the ability of the stem to produce such roots. Some stems which do not touch the ground produce aerial roots ; remarkable instances of this are found in the banian and the mangrove, and on a smaller scale in Indian corn, which for several joints above the soil throws out what farmers call brace roots, some of which reach the soil, while others do not ; in the European ivy, the poison sumach, trumpet-creeper, and other climbers, the stem produces roots which are completely diverted from the usual office of the root and serve only to aid the plant in climbing, their main use being to attach them to the trees 01 which they grow, like the roots of epiphytes. The Stem. The forms presented by the stei are still more numerous and varied ; its prop- er function is to lift up the leaves to the influ- ences of the light and air, and to keep up communication between those organs and the root, as well as (generally) to bear the repr ductive organs. The differences in duration the stem are similar to those of the root ; tl great variety in size, from the mere thread-lik( stem of some vines to the trunks 30 ft. or moi in diameter of the giant trees of California Australia, need only be alluded to. The din tion of the stem, from the prostrate form of cucumber, through the reclining stem of the
 * it may grow, presents a succession of leaf-