. Outlines of plant life : with special reference to form and function . Botany. THE STEM. 89 The paired vascular strands within the stele occupy various positions, and for purpose of location may be spoken of as though single. If trans- verse sections of the stem are observed, they may be seen either in a sin- gle row, roughly parallel with the surface of the stem (fig.'72), or in several concentric rows (fig. 79), or they may be irregularly disposed throughout it (fig. 73). No one method of arrangement is confined to any of the larger groups of plants, although the first is characteristic of
. Outlines of plant life : with special reference to form and function . Botany. THE STEM. 89 The paired vascular strands within the stele occupy various positions, and for purpose of location may be spoken of as though single. If trans- verse sections of the stem are observed, they may be seen either in a sin- gle row, roughly parallel with the surface of the stem (fig.'72), or in several concentric rows (fig. 79), or they may be irregularly disposed throughout it (fig. 73). No one method of arrangement is confined to any of the larger groups of plants, although the first is characteristic of most. Fig. 79.—Transverse section of the aerial stem of an onion {Allium Schoenoprasuin). e, epidermis ; ch, chlorophyll-bearing tissue of cortex; r, colorless tissue of cortex; ^,^, vascular bundles (wood bundles black, bast bundles dotted); sr, mechanical tissues connected into a cylinder; 7n, pith; ky pith canal formed by destruction of cells. Magnified 30 diam.—After Sachs. dicotyledons, while both the second and third methods are common among the monocotyledons. But so many exceptions are found to these last statements that it is best not to indicate the arrangement of the bun- dles by the terms dicotyledonous or monocotyledonous, as has been com- monly done; nor is it possible to maintain the terms exogenous and en- dogenous, which have long since become obsolete because misleading. 110. Pith.—^The pith is frequently found enormously developed in those parts of the stem used for storing reserve food, such as the tubers of the white potato and the yam. In other plants, particularly those growing in water, it suffers. 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 Barnes, Charles Reid, 1858-1910. New York : Henry Holt and Company
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