. Practical botany. Botany. 484 PRACTICAL BOTANY (7) Reduction of leaf surface, as in the case of needle-shaped (Fig. 248), scale-like, or other small, narrow kinds of leaf. (8) Partial or complete absence of useful leaves, as in the " switch plants," such as Spartium, Casuarina (Fig. 365), and so on; and in asparagus, the cacti (Fig. 65), and some euphorbias (Fig. 366). 445. Discussion of xerophytic characters. The first four kinds of characters operate, as may be readily under- stood, greatly to limit the loss of water. Close- ly packed parenchyma cells m the leaf interior, with fe
. Practical botany. Botany. 484 PRACTICAL BOTANY (7) Reduction of leaf surface, as in the case of needle-shaped (Fig. 248), scale-like, or other small, narrow kinds of leaf. (8) Partial or complete absence of useful leaves, as in the " switch plants," such as Spartium, Casuarina (Fig. 365), and so on; and in asparagus, the cacti (Fig. 65), and some euphorbias (Fig. 366). 445. Discussion of xerophytic characters. The first four kinds of characters operate, as may be readily under- stood, greatly to limit the loss of water. Close- ly packed parenchyma cells m the leaf interior, with few air spaces, give little opportunity for the water in the interior cells to escape into the internal atmos- phere of the leaf and so gradually pass off into the air. When the epi- dermis is thick, espe- cially if it is covered with a heavy, water- proof cutinized layer («<, Fig. 364), transpi- ration when the stomata are closed is very scanty. Stomata situated at the bottoms of microscopic pits or furrows are much protected from drafts of air and therefore give oif vapor slowly. And when the stomata-bearing leaf surface, as in the. Fig. 365. Casuarina, an Australian switch plant destitute of foliage leaves and depend- ing on the chlorophyll-containing cells of the bark for photosynthesis Photograph hy Robert Cameron. 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, Otis William, 1869- joint author. Boston, New York [etc. ] Ginn and company
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