File:College botany; structure, physiology and economics of plants (1920) (20539398028).jpg

Title: College botany; structure, physiology and economics of plants
Identifier: cu31924000606685 (find matches)
Year: 1920 (1920s)
Authors: Cook, Melville Thurston, 1869-1952
Subjects: Botany
Publisher: Philadelphia and London, J. B. Lippincott Company
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN

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74 COLLEGE BOTANY it -will be readily seen that the leaves miist have a very definite relationship to both air and stinlight. Looking upward into the top of a tree, it will be seen that the leaves are on or near the tips of the shoots and form a canopy supported by the branches as a framework; or, looking down on the tree, it will be noted that there is very little overlapping of the leaves, which are so arranged as to form a beautiful mosaic. These: p^rimary func- tions will be given further consideration in Chapters XIV and XVI. The secondary functions of the leaves are as follows: (a) Storage, in which the leaves are fleshy and usually serve to supply nour- ishment for flower and fruit stalks, which are produced later. The so-called cen- tury plant is a good example of this kind, but the cabbage plant is a much more common example. The cabbage is a bienuial which produces its flowers and seeds the second year, using the food that was stored in the leaves during the Fig. 55.—Barberry leaves " modified into spines. £j.g^ SOaSOu's grOWth. (6) Leaves serve as hvd sccdesfov the protection of the true leaves and the flowers within. By carefully removing the scales there vsdll be found a gradual gradation from true scales on the outside to true leaves within (Fig. 20). (c) Leaves are frequently developed as spines, in which the veins become firm and shaxp, and the mesophyll is greatly re- duced. The barberry is an excellent example of this type of leaf (Fig. 55).
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