Page:Popular Science Monthly Volume 19.djvu/560

544, the young growing extremities of which are protected by a layer of tissue called the root-cap. The stem is the axis of the plant, and is the part which bears the leaves, and includes those peculiar growths, such as thorns, runners, tendrils, etc., which serve a special purpose in the plant economy. The leaf is a lateral outgrowth from the stem, and is usually a flat, green expansion, but may assume the form of scales, highly-colored and strangely-shaped floral parts, etc. The fact that the largest tree and the smallest herb are alike made up of a greater or less number of these plant-members, as they are termed, leads naturally to the thought that any mass of plant-tissue having a root, a stem, and a leaf, may be a plant individual, and that, when a number of these members are intimately associated together, a community of plant individuals is formed. This is the modern conception of a tree or shrub—a living structure, which is the result of the combined, harmonious, silent working of many generations of individuals. Out of the three members are made all the multiplicity of forms and structures which meet our eyes as we look upon the higher forms of vegetation. They all have a common origin in the apical growing-points, and are indistinguishable in their earlier stages, but become differentiated as they develop, and at last assume their characteristic, mature forms. The growing-point of a stem (punctum, vegetationis) is a conical apex, a little below which the leaves appear first as very slight swellings. By their more rapid growth than the stem, they reach above the growing-point, and, folding over each other, cover it more or less completely. As the stem elongates, the leaves upon the older portion are gradually separated, and an ordinary stem, with its leaves arranged at regular intervals, results. A bud is simply a young stem, with its undeveloped leaves. A developed stem is a series of similar parts, those parts being a leaf with a portion of the stem above and below it, each borne upon its predecessor, and in turn bearing the next one in the series. These similar parts have received the name phyton, and are very generally considered as the individuals out of which a plant community is built up. The gardener divides the young branches of the verbena, salvia, etc., into these phytons, and places them in moist sand, where they soon begin an independent existence, and in time reproduce their kind. In the operation of grafting, a similar portion of a plant community of one variety is given a fitting place for growth in another, and by its growth and multiplication of phytons a new colony is established. With this view a tree or shrub may form an individual part of a landscape, but not in the same sense that one may speak of a cow or a horse. The tree more nearly resembles a swarm of bees; there is a similarity of unity between a shrub and a hive. The larger part of the shrub is made up of foliar units, with ordinary leaves for the elaboration—gathering, so to speak, of the food for the whole community. These are the workers and the neuters of the vegetable "hive." Other plant