. Botany all the year round; a practical text-book for schools. Botany. STEM FORMS AND USES I45 and air. In general, leaves seek the best possible light exposure, and hence the normal growth of the stem is upward, toward the Hght. There are exceptions, how- ever, in the case of shade-loving plants that seek the shelter of the forests, and certain winter green herbs like the chickweeds, Indian strawberry, and dandelion, that protect themselves against stress of weather by lying low and hugging the earth. The same habit may temper both the summer's heat and winter's cold, by shading the earth ar
. Botany all the year round; a practical text-book for schools. Botany. STEM FORMS AND USES I45 and air. In general, leaves seek the best possible light exposure, and hence the normal growth of the stem is upward, toward the Hght. There are exceptions, how- ever, in the case of shade-loving plants that seek the shelter of the forests, and certain winter green herbs like the chickweeds, Indian strawberry, and dandelion, that protect themselves against stress of weather by lying low and hugging the earth. The same habit may temper both the summer's heat and winter's cold, by shading the earth around the roots and preventing too rapid evaporation in the hot season, and by keeping them in contact with the warm earth and preventing too rapid radiation in winter. 206. The Surface of Stems, like that of leaves, may be hairy, prickly, smooth, rough, etc., and the same terms are used in describing them. The object of these adaptations is the same as in leaves. Grooves and wings and hairs may either be related to drainage and aid in the conduc- tion of water, or they may help or hinder the visits of certain insects and other animals. Some of these devices are very ingenious, and have been imitated by man. The sticky gum exuded from the upper nodes of the catchfly {Silene) protects the flower against the visits of crawling insects as effectively as would a strip of sticky fly paper; and our barbed-wire fences do not serve their purpose any better than the prickles of the black- berry and the cactus. In regard to 207. Shape, stems are either round (terete), flattened, square, triangular, etc. Sometimes the shape is of great use in helping to distinguish different kinds of plants. In the mint family and its allies, square stems are prevalent; the sedges are generally characterized by triangular ones, and grasses by round, hollow, jointed ctilms, or haulms, as they are called, like those of wheat, oats, and rye. 288. — Culm of millet. ANDREWS'S BOX. — lO. Please note that the
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