. Principles of modern biology. Biology. in plants are turgor movements involving receptor-conductor-effector structures similar to those of Mimosa. Accordingly, (1) the drooping of leaves during rainfall, (2) the movements by which leaves and flowers fol- low the course of the sun, (3) the leaf-closing movements by which insectivorous plants trap their living prey (Fig. 14-2), and (4) the sleep movements of many plants (Fig. 14-3) are all considered as typical turgor move- ments. GROWTH MOVEMENTS An example of growth movement is the bending of young stems toward a source of light (Fig. 14-4).
. Principles of modern biology. Biology. in plants are turgor movements involving receptor-conductor-effector structures similar to those of Mimosa. Accordingly, (1) the drooping of leaves during rainfall, (2) the movements by which leaves and flowers fol- low the course of the sun, (3) the leaf-closing movements by which insectivorous plants trap their living prey (Fig. 14-2), and (4) the sleep movements of many plants (Fig. 14-3) are all considered as typical turgor move- ments. GROWTH MOVEMENTS An example of growth movement is the bending of young stems toward a source of light (Fig. 14-4). Such growth movements proceed so slowly that about an hour is re- quired to appreciate the change. Growth The Responses of Higher Plants - 261 movements tend to be irreversible. The bend- ing depends upon a faster lengthwise growth of the cells on one side of the stem, and the convexity of the curvature always lies on the side of faster growth (Fig. 14-4). The fundamental difference between growth and turgor movements was not clari- fied until 1910, when evidence began to ac- cumulate proving the existence of growth substances, which regulate the growth of cells in different parts of the plant. Previ- ously it was known that cutting off the meri- stem tissue at the tip of a stem stops growth in the cells of the stump, where normally the cells continue to elongate until they be- come fully differentiated. The situation re- mained obscure, however, until about 1930. Then as a result of the researches of Boysen- Jensen, in Denmark, and Frits Went, in. Fig. 14-2. Venus's-flytrap (Dionaea), catching and digesting a fly. This move- ment is a turgor movement. (Copyright, General Biological Supply House, Inc.). 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 Marsland, Douglas, 1899-. New York, Holt, Rinehart and Wi
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