KINDS OF SHOOTS.
691. Since it is desirable to consider the shoot in its relation to environment, for convenience in discussion we may group shoots into four prominent kinds: (1) Foliage shoots; (2) Shoots without foliage leaves; (3) Floral shoots; (4) Winter conditions of shoots and buds. Topic (4) will be treated in [Chapter XXXIX, section IV].
Fig. 413.
Lupinus perennis.
Foliage shoot and floral shoot.
692. (1st) Foliage shoots.—Foliage shoots are either aerial, when their relation is to both light and air; or they are aquatic, when their relation is to both light and water. They bear green leaves, and whether in the air or water we see that light is one of the necessary relations for all. Naturally there are several ways in which a shoot may display its leaves to the light and air or water. Because of the great variety of conditions on the face of the earth and the multitudinous kinds of plants, there is the greatest diversity presented in the method of meeting these conditions. There is to be considered the problem of support to the shoot in the air, or in the water. The methods for solving this problem are fundamentally different in each case, because of the difference in the density of air and water, the latter being able to buoy up the plant to a great degree, particularly when the shoot is provided with air in its intercellular spaces or air cavities. In the solution of the problem in the relation of the shoot to aerial environment, stem and leaf have in most cases coöperated;[38] but in view of the great variety of stems and their modifications, as well as of leaves, it will be convenient to discuss them in separate chapters.
Fig. 413a.
Burrowing type, the mandrake,
a “rhizome.”
693. (2d) Shoots without foliage leaves.—These are subterranean or aerial. Nearly all subterranean shoots have also aerial shoots, the latter being for the display of foliage leaves (foliage-shoots), and also for the display of flowers (flower-shoots). The subterranean kinds bear scale leaves, i.e., the leaves not having a light relation are reduced in size, being small, and they lack chlorophyll. Examples are found in Solomon’s seal, mandrake ([fig. 413a]), etc. Here the scale leaves are on the bud at the end of the underground stem from which the foliage shoot arises. Aerial shoots which lack foliage leaves are the dodder, Indian-pipe-plant, beech drops, etc. These plants are saprophytes or parasites (see [Chapter IX]). Deriving their carbohydrate food from other living plants, or from humus, they do not need green leaves. The leaves have, therefore, probably been reduced in size to mere scales, and accompanying this there has been a loss of the chlorophyll. Other interesting examples of aerial shoots without foliage leaves are the cacti where the stem has assumed the leaf function and the leaves have become reduced to mere spines. The various modifications which shoots have undergone accompanying a change in their leaf relation will be discussed under stems in [Chapter XXXIX].
694. (3d) Floral shoots.—The floral shoot is the part of the plant bearing the flower. As interpreted here it may consist of but a single flower with its stalk, as in Trillium, mandrake, etc., or of the clusters of flowers on special parts of the stem, termed flower clusters, as the catkin, raceme, spike, umbel, head, etc. In the floral shoot as thus interpreted there are several peculiarities to observe which distinguish it from the foliage shoot and adapt it to its life relations.
The floral shoot in many respects is comparable to the foliage shoot, as seen from the following peculiarities: