. Plant studies; an elementary botany. Botany. 198 PLANT STUDIES surface of the globular, cylindrical, or flattened stems (see §36). 140. Hairy coverings.—A covering of hairs is an effective sun screen, and it is very common to find plants of xerophyte regions character- istically hairy (see §35). The hairs are dead struc- tures, and within them there is air. This causes them to reflect the light, and hence to ap- pear white or nearly so. This reflection of light by the hairs dimin- ishes the amount which reaches the working region of the plant (see Fig. 174). 141. Bodyhabit. —Besides the va-
. Plant studies; an elementary botany. Botany. 198 PLANT STUDIES surface of the globular, cylindrical, or flattened stems (see §36). 140. Hairy coverings.—A covering of hairs is an effective sun screen, and it is very common to find plants of xerophyte regions character- istically hairy (see §35). The hairs are dead struc- tures, and within them there is air. This causes them to reflect the light, and hence to ap- pear white or nearly so. This reflection of light by the hairs dimin- ishes the amount which reaches the working region of the plant (see Fig. 174). 141. Bodyhabit. —Besides the va- rious devices for diminishing ex- posure or leaf sur- face, and hence loss of water, enumerated above, the whole habit of the plant may em- phasize the same purpose. In dry regions it is to be observed that dwarf growths prevail, so that the plant as a whole does not present such an exposure to the dry air as in regions of greater moisture (see Fig. 175). Also the pros-. Fig. 175. Two plants of a common scouring rush (.ESyat- selum), showing the effect of environment; the long, unbranched one having grown in normal meeophyte conditions ; the short, bushy branching, more slender form having grown on the dunes (xerophyte condi- tions).—After 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. New York, D. Appleton and Company
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