. Practical botany. Botany. 482 PRACTICAL BOTANY. (2) The various kinds of heather, knotgrass (^Polygonum amculare), Itnawel (^Scleranthus annuus'), and the rushes are instances of xerophytes with small leaves, exposing compara- tively little surface to the sun and air. (3) Century plants (Fig. 62), houseleeks, and aloes are good examples of fleshy-leaved xerophytes. (4) Many xerophytes combine in their leaves some of the characteristics of groups (1), (2), and (3). The leaves of cedars, hemlocks, firs, and spruces have a thick epidermis and close interior struc- ture, like that shown in Fig.
. Practical botany. Botany. 482 PRACTICAL BOTANY. (2) The various kinds of heather, knotgrass (^Polygonum amculare), Itnawel (^Scleranthus annuus'), and the rushes are instances of xerophytes with small leaves, exposing compara- tively little surface to the sun and air. (3) Century plants (Fig. 62), houseleeks, and aloes are good examples of fleshy-leaved xerophytes. (4) Many xerophytes combine in their leaves some of the characteristics of groups (1), (2), and (3). The leaves of cedars, hemlocks, firs, and spruces have a thick epidermis and close interior struc- ture, like that shown in Fig. 249, and are also small, exposing little surface. The common purslane, the portu- laca, and the ice plants {Mesembryanthemum) have small and rather fleshy leaves. Many xerophytes have extraordmarily developed root systems, as in the case of the mesquite (Sect. 27), and so can draw moisture from great depths in the earth. Others have extensive provisions for water storage (Sects. 34, 66, 67). Among these the cacti are notable for the amount of water which they can store in their succulent stems, which are often fluted, so as to expand and contract readily. This water has been rapidly absorbed by the spreading, shallow root system from the layer of earth (only an inch or two deep), which is moistened by the rare rains of the desert re- gions where many such cacti grow. Between rains the roots of these cacti serve only for anchorage. Xerophytes in general are so constituted as to transpire little at any time, or else to be able, in ciise of danger from excessive dryness, to reduce the amount of transpiration to a very low value. Fig. 363. Cross section of rolled-up leaf of crowberry (Empetrum nigrum) Magnified. 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 Bergen, Joseph Y. (Joseph Young), 1851-1917; Caldwell
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