42 RESEARCHES ON FUNGI 



be used for demonstrating the way in which light is refracted through 

 a subsporangial sweUing, was also described, and it was announced 

 that a fuller description of my observations, accompanied by illus- 

 trations, was in preparation for the press. The more elaborate 



Fig. 15. — Pilobolus Kleinii. Result of a heliotropic experiment in which 

 the sporangiophores were illuminated with two equal beams of white light 

 which converged on each fruit-body at a relatively wide angle (about 

 25°). Natural-size reproduction of a photographic print made 

 directly from a sheet of glass which covered two openings in the 

 side of a dark chamber. The positions of the openings, each 

 1-0 X 0-5 cm., have been indicated by white lines. The discharged 

 sporangia, which adhered to the sheet of glass and were black, appear 

 as white dots. Direction of shooting was horizontal. Distance of the 

 vertically placed surface of the culture medium from the glass plate 

 was 12 cm. The distance between the two windows, measured from 

 centre to centre, was 5 • 5 cm. The sporangiophores were continuously 

 lighted during the whole course of their development. From the dis- 

 tribution of the discharged sporangia it is evident that the spor- 

 angiophores directed themselves toward one or other source of light 

 and not in the resultant direction midway between them. Photo- 

 graph bv Van der Wev (Proc. K. Akad. v. Wetensch. te Amsterdam, 

 Vol. XXXII, 1929, Plate I, Fig. 5). 



treatment of the ocellus function of the subsporangial swelling 

 promised thirteen years ago was completed at that time ; but, 

 owing to my pre-occupation with other investigations, its pubUca- 

 tion has been delayed until now : it will be found in the next chapter 

 of this book. 



The Solution of the Problem of the Non-resultant Heliotropic 

 Reaction of Pilobolus to Two Beams of Light.— In 1927, Pringsheim 



