. Practical botany. Botany. ECOLOGICAL GROUPS 483 In order to realize the extreme danger to which plants are exposed from dryness, one needs only to remember how often harvests in great part fail from the effects of drought. This may mean that the entire plants have been killed, or only that they have not borne much fruit or seed, or that the roots, stems, or leaves are stunted. ^Nlany wild plants are as sensitive to prolonged drought as are ordinary field crops, and irrigation of a desert region which has a rich soil helps the growth of weeds as much as it does that of the crops among which t
. Practical botany. Botany. ECOLOGICAL GROUPS 483 In order to realize the extreme danger to which plants are exposed from dryness, one needs only to remember how often harvests in great part fail from the effects of drought. This may mean that the entire plants have been killed, or only that they have not borne much fruit or seed, or that the roots, stems, or leaves are stunted. ^Nlany wild plants are as sensitive to prolonged drought as are ordinary field crops, and irrigation of a desert region which has a rich soil helps the growth of weeds as much as it does that of the crops among which they spring up. 444. Means of limiting transpiration. Some of the principal means of limiting transpiration are as follows ^ : (1) Compact arrangement of the parenchyma cells in the interior of the leaf. (2) Development of a thick-walled epidermis (Figs. 249 and 364). (3) Situation of the sto- mata in pits or furrows (Figs. 249 and 364). (4) Inclosing the stomata in a sort of tubular cavity formed by the curving-in of the margins of the leaf (Fig. 363). (5) Presence of a coating of dead hairs, filled with air, on one or both surfaces of the leaf (Fig. 57). (6) Temporary reduction of the evaporating surface, as by rolling up leaves (Fig. 2), shedding leaves, reduction of living parts to a buried root, bulb, tuber, rootstock, or some combination of thickened roots and underground stems. 1 The subject is a very extensive one, fully treated in the writings of Warming, SoMmper, Goebel, Volkens, and other Fig. 364. "Waterproof epidermis and protected stoma of the century plant c, cuticle; cu, cutinized (waterproofed) layer of epidermis; ce, cellulose layer of epidermis; pi, pit, at the bottom of which the stoma is situated; po, pore of the stoma. Magnified about 220 diameters. After Luerssen. 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
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