. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. Plant anatomy. 98 ABSORPTION OF WATER AND MINERALS and both are thickly beset with overlapping scales under which rain and dew gather and find entrance by osmosis into the cell cavities. Here the scales, like the velamen, serve both for the absorption, of water and protection against its loss. The scales when dry are shrunken and lie close against the stem or leaf; but when wet their thicker outer wall swells and bulges outward,. Fig. 47.—Cross section through a water-absorbing s
. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. Plant anatomy. 98 ABSORPTION OF WATER AND MINERALS and both are thickly beset with overlapping scales under which rain and dew gather and find entrance by osmosis into the cell cavities. Here the scales, like the velamen, serve both for the absorption, of water and protection against its loss. The scales when dry are shrunken and lie close against the stem or leaf; but when wet their thicker outer wall swells and bulges outward,. Fig. 47.—Cross section through a water-absorbing scale o£ Tillandsia usneoides; o, o, water- absorbing cells partially filled with water. (After Schimper.) water is drawn into the cell cavities, and by their turgidity the scales rise and make room for more water beneath them (Fig. 47). Practically the whole plant body is thus enabled to imbibe water, -and solutes that have come in the form of dust. Other Methods of Absorbing Water.—Some desert plants have devices for absorbing water into the leaves. Diplotaxis Harra, for example, a cruciferous plant of the Egyptian and Arabian deserts, has its foliage beset with stifE hairs which, acting as points for the radiation of heat, after sunset gather dew. The hair is practically waterproof excepting at its base, where the dew, running down from above, forms a filrn over the wall and 'is quickly absorbed. There are some interesting anatomical details in these hairs of Diplotaxis (Fig. 48). Cellulose additions to the wall fill the cell cavity down to the spreading base, where the cavity enlarges and is lined with an unusually thick protoplastic layer. The wall separating the hair from the body of the leaf has many pits through which the imbibed water can pass into a water reservoir tissue beneath, whence it is distributed directly to the mesophyll cells. The entire leaf is so thoi-oughly waterproofed that only. Please note that these images are extracted from scanned page images t
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