VEGETATION. The complex problems in vegetable life, and in the act of vegetation, have caused it to be made the careful study of some of the most profound thinkers of the present day. In the articles, Germination and Physi ology, some branches of these questions are noticed. A plant from the time it begins its growth either from the seed or bud, simply mul tiplies cell growth until the limit of its vegeta tive powers are naturally reached, or until growth is stopped by sonic extraneous cause. The plantlet having reached the surface of the ground, moisture and heat must be supplemented with light, under which the stem and leaves be come green and immediately begin to elaborate nutriment from the watery sap drained by the roots from the earth. The roots continue to ex tend, thus increasing their powers of absorption, the leaves above ground continue to multiply, thus increasing the power of elahoration, and as a rule in just proportion to the root, so will be the proportion of leaf surface of a plant. The seedling has all the organs of the perfect plant, except the blossom buds, and these, as have been shown in another part of this work, are simply modified leaf buds. Thus it simply has to grow and produce in duplicate. what it already possesses. Thus the stem is carried higher and higher, and in plants having more than a simple stem, side branches are produced, as in the oak, each branch, nay each bud representing the ulti mate perfect plant, each increasing, and with continued powers of increase, until the mature stage is reached and growth ceases. In the case of annuals, this occurs at the end of the season with the ripening of the seed. With biennials, it occurs at the end of the second year. With triennials the third year, and with perennials, this growth continues indefinitely, particular species of trees wanting 5,000 or even more years to complete their growth. Some plants die down to the ground at the end of the season, the nutriment for the succeeding year's growth be ing started frorn year to year, as in the case of herbaceous biennials and perennials, or as in the case of deciduous trees, that store elaborated sap next the bark, and in the buds, but drop their leaves at the end of the season. In the case of evergreens, the leaves remain persistent, for one or more years, sometimes for five or six years, the new growth being supplied from the annual buds, as in the cone bearing trees, or else buds open succe,ssively as in the case of some tropical forms of vegetation. Vegetation may therefore be divided into annuals, biennials, and perenni als, since as a rule the so-called triennials are simply biennials, that under abnormal condi tions survive to the third year. Annuals, then, store up their life germs in the seed; biennials in the roots, the first season, expending this the second season in flowering and fruiting. By stopping the flowering, biennials may be made to continue to the third season, and some annuals may be changed into biennials, as in the case of winter wheat, strictly an annual plant. So bien
nial plants may bear fruit the first year. The organs of vegetation are three, the root, the stem, and the leaf. The form and appearance which these take are diverse, and yet however wonder ful, still each may be traced to one of the three organs. This study is called morphology. The root is the simplest form, consisting of the primary root, and its branches, there are, how ever, suhterranean, and aerial roots. Indian corn gives us an example among annual plants; the Pea-nut throws out aerial roots, which striking into the earth the nuts are formed thereon; the Banyan tree is an example among perennial trees, of aerial roots starting from the branches high in air, growing downward until they reach and pierce the soil, and forming additional props or trunks to the parent tree. So aerial roots are formed on a small scale by various climbing plants, as the Trumpet creeper, Poison ivy, the Virginia creeper, the English ivy, etc. So orchids or air plants, have nothing but aerial roots, and sustain themselves as parasites on other plants. The Mistletoe, Dodder, and vari ous fungus plants. are well known parasitic plants. The stem as to form or kind is dis tinguished as belonging to herbs, shrubs and trees. It is herbaceous, if it die down in the autumn. It is denominated shrubby if it is woody, lives over the winter, and belongs to those trees denominated shrubs, or it is arbores cent when belonging to tall trees of a single stem. It is upright when it grows erect; ascend ing when it rises in a slanting direction; declin ing when bent or turned to one side; decumbent when it lays along the ground but with the end turned more or less upward; procumbent when the whole stem trails along the ground; pros trate when it naturally lies flat on the ground:, creeping, if postrate and taking root along its. lower side where it rests on the ground; climb ing when it rises by means of tendrils, as in the grape, or by twisting its leaf-stalk around the support, as in the Maurandia, or by its rootlets, as in the ivy; it is twining when the stem sup ports it by winding spirally about a support, as in the bop or bean. The Squash is a climbing plant, yet if it have no support it becomes a creeping plant, anchoring itself to the ground by roots thrown out at the joints. The Straw berry is a true running plant. It forms no ten drils, but does throw out runners, forming an independent plant at the end of the runner. The leaf of a plant forms the organ correspond ing to respiration and digestion. These forms are almost endless in variety, and yet in a given. species, afford a means for distinguishing the species. A complete leaf has a blade, the extended portion above the footstalk; a foot stalk, the portion connecting it with the stem ;_ and a pair of stipules, or a pair of little blades at the base of the footstalk next the stem. The quince has this perfect leaf, many leaves have no stipules, manST .have no footstalk but sit directly on the stem. Some indeed have no blade, but this is rare.