. Botany all the year round; a practical text-book for schools. Botany. 244 ECOLOGY air cavities, and the bases of the stems are often greatly enlarged, as in the Ogeechee lime {Nyssa capitaia) and cypress, to give room for the formation of air passages. The peculiar hollow projections known as " cypress knees " are arrangements for aerating the roots of these trees. 350. Xerophyte Societies are adapted to conditions the reverse of those affected by hydrophytes. The extreme of these conditions is presented by regions of perennial drought like our western arid plains and the great des
. Botany all the year round; a practical text-book for schools. Botany. 244 ECOLOGY air cavities, and the bases of the stems are often greatly enlarged, as in the Ogeechee lime {Nyssa capitaia) and cypress, to give room for the formation of air passages. The peculiar hollow projections known as " cypress knees " are arrangements for aerating the roots of these trees. 350. Xerophyte Societies are adapted to conditions the reverse of those affected by hydrophytes. The extreme of these conditions is presented by regions of perennial drought like our western arid plains and the great deserts of the interior of Asia and Africa. Under these conditions. 469. — "Switch plants "of the alkali desert, condensed into mere green skeletons of vegetation, and thus adapted to extreme xerophyte conditions. plants have two problems to solve; to collect all the mois- ture they can and to keep it as long as they can. Hence, plants of such regions diminish their evaporating surface by reducing or getting rid of their foliage and compacting all their tissues into the Stem, like the cactus (Sec. 209), or they compress their leaves into thick and fleshy forms fitted to resist evaporation and retain large amounts of moisture, as in the case of the yucca and century plant. They also frequently develop a thick, hard epidermis, or cover themselves with protective hairs and scales. 351. Examination of a Xerophytic Plant. — Examine a joint of the common prickly pear {Optmtid), if it grows in your neighborhood, or use a potted cactus, and give your reasons for regarding it as a stem and not as a 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 Andrews, Eliza Frances, b. 1840. New York, Cincinnati [etc. ] American book company
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