. Elementary botany. Botany. IRRITABILITY. 87 flower plant in the experiment detailed above. The day position of the leaves on the other hand, which is more or less horizontal, is induced because of their irritability under the influence of light, the inherent downward or epinastic growth is overcome for the time. Then at nightfall or in darkness, the stimulus of light being removed, the leaves assume the position induced by the direction of growth. In the case of the cotyledons of some plants it would seem that the growth was hyponastic even after they have opened. The day position of the cot
. Elementary botany. Botany. IRRITABILITY. 87 flower plant in the experiment detailed above. The day position of the leaves on the other hand, which is more or less horizontal, is induced because of their irritability under the influence of light, the inherent downward or epinastic growth is overcome for the time. Then at nightfall or in darkness, the stimulus of light being removed, the leaves assume the position induced by the direction of growth. In the case of the cotyledons of some plants it would seem that the growth was hyponastic even after they have opened. The day position of the coty-. Position of cotyledons in the dark. Fig. 77. Fig. 78. Squash seedling. Position of cotyledons in Squash seedling, light. ledons of the pumpkin is more or less horizontal, as shown in fig. 77. At night, or if we darken the plant by covering with a tight box, the leaves assume the position shown in fig. 78. While the horizontal position is the general one which is assumed by plants under the influence of light, their position is dependent to a certain extent on the intensity of the light as well as on the incidence of the light rays. Some plants are so strongly heliotropic that they change their posi- tions all during the day. 203. Leaves with a fixed diurnal position.—Leaves of some plants when they are developed have a fixed diurnal position and are not subject to. 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 Atkinson, George Francis, 1854-1918. New York, H. Holt
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