Page:The American Cyclopædia (1879) Volume XIII.djvu/593

 PLANT 577 wild currant, and the twining stem of the hop, up to the erect one of the forest tree, presents a great number of modifications, all of which in descriptive botany have their technical names. Perennial stems, such as trees, are usually ter- minated by a bud ; this preparation to con- tinue the growth of the stem is made during summer, and when such buds are examined they are found to contain rudimentary leaves crowded upon very short undeveloped inter- nodes; in the following spring growth from such buds is exceedingly rapid ; the internodes elongate, while at the same time the minute leaves develop, and in many trees the whole growth of the season is made in a short time. The terminal buds only prolong the main stems, but most stems branch, and the branches (as a rule) proceed from buds in the axils of the leaves, or where these join the stem ; as leaves are opposite or alternate, the branches are thrown off in a similar manner ; but as only a small portion of the axillary buds develop, the arrangement of the branches is not so symmet- rical as might be expected. In trees and shrubs the buds, both terminal and axillary, are pre- pared beforehand and remain dormant through the winter. In many cases the development is continuous, especially in annual stems ; buds are developed as soon as formed, and we find upon such stems every gradation between the fully developed internodes, through gradually shorter ones, to a loose bud or growing point. Buds which are neither terminal nor axillary, but which appear anywhere upon the stem, are termed adventitious ; some trees and shrubs produce them habitually, while others do so only when the regular buds have been de- stroyed. To some forms of the stem special names are given, some of which are in common use ; a weak prostrate stem, like that of the strawberry, is a runner ; a sucker is a branch starting upon the stem at a point below the surface of the soil ; a stolon is a stem which bends over and takes root at the end ; these are all taken advantage of in propagating plants. In some cases a branch is developed as a ten- dril to aid the plant in climbing ; there are ten- drils of a different nature, but a fine example of this form is afforded by the beautiful Vir- ginia creeper, in which a slender branch^has at the end of each subdivision a disk which at- taches itself to a wall, after which the branch coils into a spiral. Thorns or spines are often suppressed branches, which become indurated and sharp at the point, as may be seen in a wild pear tree, the thorns, and many of the shrubs belonging to the arid western plains, where al- most all vegetation seems to be on the defen- sive. In most of the cactus family the leaves are mere rudiments which soon fall away, and the thick, green, fleshy rind of the stem per- forms the functions of both leaf and stem. These are a few of the above-ground forms of the stem, but those found below the sur- face are nearly as numerous and varied; much of that portion of the plant which, be- ing found below ground, is popularly con- sidered as the root, really consists of branch- es belonging to the stem. As there are creep- ing stems, which lie upon the surface and throw out roots at each joint or node, so there are plants with similar stems which behave in the same manner just below the surface ; these stems have nodes, from which roots proceed; but having no use for leaves, these organs are represented by mere rudi- ments in the form of scales; they have ter- minal and axillary buds, and if separated from the plant are capable of living, and if they are cut into as many pieces as there are joints, each node is able to make a plant ; some weeds, eminently couch grass, and some sedges in sandy soils, have underground stems of this kind, which ordinary cultivation only breaks up and subdivides, and thus multiplies rath- er than destroys the weed. Such an under- ground stem is called a rhizome or root- stock, which may be slender as in the couch grass, or very much thickened and fleshy as in the iris, bloodroot, and many others ; in some the growth is very slow and definite, as in the Solomon's seal of our woods (smila- cina), which throws up its leafy stem, and du- ring the season matures a bud at its extrem- ity ; when the stem dies it leaves a scar on the rootstock ; the bud thus formed will produce an above-ground stem the next year, another bud will be formed in advance of it, and so on, the plant gradually moving forward in this manner, while the older part of the rootstock, being no longer of use, slowly decays. Anoth- er form of the rootstock is the tuber, as the potato, which is only a very fleshy rootstock, gorged with starch to serve as nutriment for the numerous axillary buds (eyes) which it bears. In the Jerusalem artichoke the rela- tionship between the tuber and the proper stem is more distinctly seen ; it appears at the end of a much shorter stem than the potato tuber, and the scales which stand for leaves are much more prominent. Another form of underground stem is furnished in the corm, which is often called a bulb ; and it is a solid bulb, or very short, more or less globular root- stock, of which among garden plants the gla- diolus and crocus, and among wild plants the Indian turnip or Jack-in-the-pulpit (ariscema), are familiar illustrations ; that these are prop- er stems, though much reduced, is shown by the leaf scars and axillary buds they bear; and that they are not proper roots is shown by their bearing distinct roots. The stem of the cyclamen is just like a corm, but grows above ground. The scaly bulb differs from the corm or solid bulb in being clothed with fleshy scales, which are the bases of the leaves, fleshy and thick with the nutriment stored in them by the upper portions of the leaves, which have fallen away. A longitudinal sec- tion of a scaly bulb, like that of a lily, shows the stem reduced to a mere plate, to the up- per surface of which the scales are attached,