. A civic biology : presented in problems. Biology; Sanitation. 74 SOIL AND ITS RELATION TO ROOTS. Cross section of a young taproot; a, a, root hairs; b, outer layer of bark; c, inner layer of bark; d, wood or central cylinder. the length of the main root. In their development the cells men- tioned have grown together in such a manner as to lose their small ends, and now form continuous hollow tubes with rather strong walls. Other cells have come to develop greatly thickened walls; these cells give mechanical sup- port to the tubelike cells. Col- lections of such tubes and sup- porting woody c
. A civic biology : presented in problems. Biology; Sanitation. 74 SOIL AND ITS RELATION TO ROOTS. Cross section of a young taproot; a, a, root hairs; b, outer layer of bark; c, inner layer of bark; d, wood or central cylinder. the length of the main root. In their development the cells men- tioned have grown together in such a manner as to lose their small ends, and now form continuous hollow tubes with rather strong walls. Other cells have come to develop greatly thickened walls; these cells give mechanical sup- port to the tubelike cells. Col- lections of such tubes and sup- porting woody cells together make up what are known as fibrovascular bundles. Root Hairs. - - Careful examina- tion of the root of one of the seed- lings of mustard, radish, or barley grown in the pocket germinator shows a covering of tiny fuzzy structures. These structures are very minute, at most 3 to 4 milli- meters in length. They vary in length according to their position on the root, the most and the longest root hairs being found near the point marked R. H. in the figure. These structures are outgrowths of the outer layer of the root (the epidermis), and are of very great importance to the living plant. Structure of a Root Hair. - - A single root hair examined under a compound microscope will be found to be a long, round structure, almost colorless in ap- pearance. The wall, which is very flexi- ble and thin, is made up of cellulose, a substance somewhat like wood in chemi- cal composition, through which fluids may easily pass. Clinging close to the cell wall is the protoplasm of the cell. The interior of the root hair is more or less filled with a fluid. 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 Hunter, George W. (George William), 1873-1948. New York : American Book Company
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