. A textbook of botany for colleges and universities ... Botany. LEAVES 601 It Would seem that the chief determining factors of leaf size and pro- portion are those that control the water supply. High transpiration, whether caused by dry air, wind, light, or high temperature, and low absorption, whether caused by dry soil, soil salts, soil toxins, low oxygen pressure, or low tem- perature, are undoubtedly the dominating influences in deter- mining the small size and the great thickness of the xerophytic leaf. Furthermore, a combina- tion of factors is more effective than any single factor, bot
. A textbook of botany for colleges and universities ... Botany. LEAVES 601 It Would seem that the chief determining factors of leaf size and pro- portion are those that control the water supply. High transpiration, whether caused by dry air, wind, light, or high temperature, and low absorption, whether caused by dry soil, soil salts, soil toxins, low oxygen pressure, or low tem- perature, are undoubtedly the dominating influences in deter- mining the small size and the great thickness of the xerophytic leaf. Furthermore, a combina- tion of factors is more effective than any single factor, both as to the rapidity of development and as to the degree of xero-^ phytism attained; an "alpine" leaf, for example, is produced most quickly by exposing a plant to intense sunlight, high tem- perature, and dry air by day,. Fig. 873. — Leaf variation in the hare- bell {Campdnula rotundifolia); the apex of the shoot has been cut off, and lateral buds have developed at b and b'\ note that the first leaves of the axillary rosettes are short and roundish, as in seedlings and basal rosettes; such an occurrence sometimes is called a reversion to a juvenile stage. — From Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Coulter, John Merle, 1851-1928; Barnes, Charles Reid, 1858-1910, joint author; Cowles, Henry Chandler, 1869- joint author. New York, Cincinnati [etc] American book company
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