120 



RESEARCHES ON FUNGI 



of the mechanism of the heliotropic reaction of Pilobolus already 

 set forth in the previous Section. 



A Solution of the Problem of the Reaction of the Sporangiophore 

 of Pilobolus to Two Equal Beams of White Light. — Allen and Joli- 

 vette ^ made a study of the reactions of Pilobolus to light, in the 

 course of which they exposed cultures of Pilobolus at one and the 

 same time to two equal beams of light which passed through two 

 holes (c/. Fig. 59, A) in the wall of a dark culture chamber. They 



Fig. 58. — Pilobolus Kleitiii. Diagram to show the reaction of a 

 fruit-body to two equal beams of light making a considerable 

 angle with one another. The directions of the two beams of light 

 are indicated by the arrows a and b. A, the beginning of the ex- 

 periment. B and C, alternative end-results of the experiment : 

 the stipe of the fruit-body has turned the sporangium and sub- 

 sporangial swelling so that these have come to face either the 

 beam-of-light a (as in B) or the beam-of-light b (as in C). 

 Magnification, 14. 



observed that, when a culture is exposed to two equal beams of white 

 light coming from two sufficiently different directions (angle between 

 the rays converging on the fruit-bodies greater than about 10° and 

 up to 36° and more), the sporangium of each Pilobolus fruit-body 

 is aimed at one or the other source of light (c/. Figs. 15, p. 42, and 

 58) and the aim is as accurate at the source of light chosen as if the 

 other source did not exist ; and they ^ commented upon this curious 

 experimental result as follows : " Light rays from both sources 

 reach the sensitive sporangiophore. Apparently there is nothing 



1 Ruth F. Allen and Hally D. M. Jolivette, " A Study of the Light Reactions 

 of Pilobolus," Trans. Wisconsin Acad., Vol. XVII, 1914, pp. 561-569, 593-594. 



2 Loc. cit., p. 593. 



