PHOTOMORPHIC ACTIONS 



97 



growth in micrometer divisions, those on the right give the temperature, which 

 is indicated by the thin line. During each half-hour's exposure to light 

 (10 to 10.30 and 11.30 to 12) the amount of growth decreased. That roots 

 grow more rapidly in darkness than in light is shown by the following results 

 obtained by Wolkoff 1 with Pisum sativum\ 



The influence of prolonged feeble illumination is well shown by the following 

 experiments by Morgen 2 , in which seedlings of Lepidium sativum were grown 

 between February 7 and March 8 at varying distances from a window. It 

 will be seen that the length of the hypocotyl increases as the light decreases, 

 although the dry weight decreases. The lessened growth of the root in the 

 more shaded plants is probably correlated with the increased growth of the 

 hypocotyl combined with the scantier supply of food. 



Light may also exercise various inductive actions, and the day's 

 exposure may influence the growth during the subsequent night. Thus, 

 in Pilobolus microsporus the tendency to sporangium formation induced 

 luring the day finds expression during the following night 3 , and similarly 

 the formation of the pileus and the elongation of the stipe of Coprinus 

 rtercorarius take place normally during the evening and night 4 . The entire 



1 Mentioned in Sachs' Textbook, p. 808. 

 a Morgen, Bot. Ztg., 1877, P- 588. 



3 Klein, Jahrb. f. wiss. Bot., 1872, Bd. vin, p. 357; Grantz, Einfluss d. Lichtes a. d. 

 Entwickelung einiger Pilze, 1898, p. 6. 



4 Brefeld, Unters. ii. Schimmelpilze, 1877, Heft 3, p. 32; Grantz, I.e., p. 23. 



PFEFFER. II H 



