. Botany for high schools and colleges. Botany. THE GELL-WALL. 33. 26.—Growth in thickness of the wall produces changes m the cell of even greater importance than growth in sur- face. While surface-growth has but little to do with the determination of the functions of the cell, the thickening of its wall generally results in a change in function, or an entire suspension of all physiological activities. Cells with extremely thin Avails are most active; only such can take part m growth. (See Chap. XI.) Nutrition and assimilation are confined to cells whose walls have but slight thick- ness. Cell
. Botany for high schools and colleges. Botany. THE GELL-WALL. 33. 26.—Growth in thickness of the wall produces changes m the cell of even greater importance than growth in sur- face. While surface-growth has but little to do with the determination of the functions of the cell, the thickening of its wall generally results in a change in function, or an entire suspension of all physiological activities. Cells with extremely thin Avails are most active; only such can take part m growth. (See Chap. XI.) Nutrition and assimilation are confined to cells whose walls have but slight thick- ness. Cells with moderately thick walls may be used as storehouses for food ; starch, for example, is frequently found in such cells. But as the walls attain great thickness the protoplasm loses all activity save that neces- sary to the secretion of cellulose. 27.—The thickening generally produces certain markings or sculpturings in the shape of projecting points, ridges, bands, etc., which on the one hand are on the outside of the wall, while on the other they are on the inside. In some pollen grains and spores we have the best examples of external markings. Here, in some cases, certain isolated points in the cell-wall become strongly thickened, g-iv- ing rise to spines or prickles (Fig. 11). Fig. 11.—Pollen grain of Lavatera trimestris, covered witu prickles. X After 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 Bessey, Charles Edwin, 1845- [from old catalog]. New York, H. Holt and company
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