. Plant physiology. Plant physiology. Fig. 130. Fig; 131. Fig. 130.—Flower of Hieracium pilosella. A, open, as by day; B, closed, as by night. Fig. 131.—Diagram showing phototropic response of Pilobolus. The culture is in a chamber and receives light only through small window at left. Spore-masses are discharged toward the window. of sixty-one different plant forms and found that the negative phototropic re- sponse was very marked in twenty-seven species and was not so marked in twenty-four species, while six species showed but little sensitiveness to light and the remaining four were not sens
. Plant physiology. Plant physiology. Fig. 130. Fig; 131. Fig. 130.—Flower of Hieracium pilosella. A, open, as by day; B, closed, as by night. Fig. 131.—Diagram showing phototropic response of Pilobolus. The culture is in a chamber and receives light only through small window at left. Spore-masses are discharged toward the window. of sixty-one different plant forms and found that the negative phototropic re- sponse was very marked in twenty-seven species and was not so marked in twenty-four species, while six species showed but little sensitiveness to light and the remaining four were not sensitive at all, This phenomenon does not occur commonly in ordinary subterranean roots, but if mustard seedlings {Sinapis alba) are grown in water-culture it is easy to demonstrate both posi- tive phototropism of the shoots and negative phototropism of the roots. Phototropic bending results from unequal growth on the two sides of the organ in which this bending occurs, and the response takes place only in the enlarging region. The degree of bending, or its rate, depends upon light intensity. Light of medium intensity produces the most pronounced bending, and the response is less marked both with higher and with lower intensities. The phototropic response is slight when the light intensity is low, increases to a >[Wiesner, 1879, 1882. [See note 2, p. 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 Palladin, Vladimir Ivanovich, 1859-1922; Livingston, Burton Edward, 1875-; Hopping, Aleita, 1890-. Philadelphia, P. Blakiston's Son & Co
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