. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. Plant anatomy. 96 ABSORPTION OF WATER AND MINERALS vides carbon dioxide and oxygen just as it does for other green plants, and brings soil substances in the form of dust. These plants are not therefore living on the air alone, as their name might imply, but they have essentially the same raw materials for building their food as have plants rooted in the soil. To illustrate the essential mode of their obtaining water and solutes two types of aerophytes will be discussed, namely, t
. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. Plant anatomy. 96 ABSORPTION OF WATER AND MINERALS vides carbon dioxide and oxygen just as it does for other green plants, and brings soil substances in the form of dust. These plants are not therefore living on the air alone, as their name might imply, but they have essentially the same raw materials for building their food as have plants rooted in the soil. To illustrate the essential mode of their obtaining water and solutes two types of aerophytes will be discussed, namely, the type where true roots are sent forth into the air, and the type which, pro- ducing no roots, has its stems and leaves equipped for ab- sorption. In the first in- stance, some tropical orchids, and other aerophytes lodging on the branches of trees, send forth roots into the air that have an external covering of dead tissue known as the velamen (Fig. 45). The cells of this tissue have many very minute openings through their exterior and interior walls through which water passes when the root is wet with rain or dew. The velamen is formed by tangential division of the protoderm, beginning a short distance from the apex and giving rise to layers of cells varying from one to eighteen or more according to the species. The cell-walls of the velamen sometimes remain thin, but usually they are thickened, either uniformly, or in the form of a network or spiral bands. After the. cells have reached maturity the protoplasts soon die, and. Fig. 45.—^Portion of a cross section through an aerial root of Stanhopea oculata. h, The velamen; i, exodermis; j, cortex; k, endo- dermis. (After Haberlandt.). 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 Stevens, William Chase, 1861-. Philadelphia, P. Blakiston's Son
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