. Nature and development of plants. Botany. NATURE OF PLANTS 59. and the cells are changing in character, so that they perform different duties. This is illustrated in the cross section of the root (Fig. 36), where we see that the outer cells have become modified, forming an epidermis with root hairs for absorption. Within the epidermis is a broad zone of cells, the cortex, often used for the stor- age of manufactured foods, while in the center of the stem are the vascular bundles. The woody portion of the bundle, or xylem, radiates out- ward from the center and the soft portion, or phloem, al
. Nature and development of plants. Botany. NATURE OF PLANTS 59. and the cells are changing in character, so that they perform different duties. This is illustrated in the cross section of the root (Fig. 36), where we see that the outer cells have become modified, forming an epidermis with root hairs for absorption. Within the epidermis is a broad zone of cells, the cortex, often used for the stor- age of manufactured foods, while in the center of the stem are the vascular bundles. The woody portion of the bundle, or xylem, radiates out- ward from the center and the soft portion, or phloem, alternates with it (Fig. 36, x, p). The materials absorbed from the soil are largely transported up to the stem and leaves through the xylem, and the foods manufactured by the leaves reach the root by means of the phloem cells. The branches of the root originate in a very curious way from the cells just outside the xylem. These cells by repeated divisions form lateral roots which gradually destroy the tissues in their way and finally grow out to the surface of the root (Fig. 37). By this arrangement they are provided with a root cap and fully prepared to enter the soil on emerging from the old root. 2S. The Transport of Water in the Root.—^The inner layer of the cortex, the endodermis (Fig. 36, end), consists of a layer of cells which, in the older part of the roots, forms a very compact and more or less cutinized ring of cells. This tissue is supposed to function in preventing an undue loss of water from the con- ducting strands of xylem to the cortex. It should be stated here that the root hairs not only absorb fluids but also force out the absorbed substances into the adjoining cells of the cortex. All living cells have this power of absorbing and expressing fluids. So it comes about that the absorbed fluids are forced by the root hairs into the cortical cells and by them they are passed on to the cells of the xylem when by some force not known they are drawn up the stem int
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