. Nature and development of plants. Botany. NATURE OF PLANTS 47 scarcely more than one millimeter in length (Fig. 30). Note that they always begin to grow a few mm. back from the root tip and at the opposite end of the zone of root hairs the tubes are withering or dying off, leaving the older portion of the root covered only with the epidermis. If a root is marked into 2 mm. spaces with India ink it will be found after 12 to 15 hours that only the portion below the root hairs is elongating. The first space from the tip has grown very little, the second and third. Fig. 29. Fig. 30. Fig. 29. The
. Nature and development of plants. Botany. NATURE OF PLANTS 47 scarcely more than one millimeter in length (Fig. 30). Note that they always begin to grow a few mm. back from the root tip and at the opposite end of the zone of root hairs the tubes are withering or dying off, leaving the older portion of the root covered only with the epidermis. If a root is marked into 2 mm. spaces with India ink it will be found after 12 to 15 hours that only the portion below the root hairs is elongating. The first space from the tip has grown very little, the second and third. Fig. 29. Fig. 30. Fig. 29. The absorbing surface of roots: A, seedling of mustard showing extent of surface covered by root hairs. B, an older branching root, the shaded areas near the tip are due to particles of earth clinging to the root hairs. The remaining portions of the root are free hairs and take little or no part in absorption. Fig. 30. Origin and character of root hairs: A, first appearance of. a root hair due to the pushing out or growth of a definite portion of the surface of an epidermal cell. B, older hairs that have become irregular through coming in contact with soil particles. much more, and in the other spaces there is a gradual retarding of the growth until 8 to 12 mm. from the tip elongation has ceased. It is at the point where elongation has ceased that the root hairs begin to appear, but the total number existing on the root at any one time does not materially vary owing to the fact that they are dying off farther back on the root with the same rapidity that characterizes their formation near the tip (Fig. 29, B). Before the significance of these peculiar features can be. 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 Curtis, Carlton Clarence, 1864-1945. New York, H. Holt
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