132 



EFFECTS OF RADIATION ON FUNGI 



the aiming was as accurate as if one source of lioht was nonexist- 

 ent. The sporangia were aimed at one or the other source of light, 

 not midway between the two. Allen and Jolivette were unable to 

 explain how this result was achieved, but Buller (1934) later 

 found the mechanical basis to reside in the ocellar structure of the 

 subsporangial swelling. 



L 



J L 



1 



J L 



J L 



J 



12 



Millimeters 



Fig. 17. Median longitudinal section of Pilobohis kleinii. The fructification 

 is directed toward the source of light. The basal sporangial wall has gelat- 

 inized, and the broken line indicates where the sporangium has separated 

 from its attachment. Certain ravs cannot penetrate the black sporangium, 

 which fits as a cap at the apex of the subsporangium. The ravs which pene- 

 trate the upper sporangial wall converge at the basal perforated septum, 

 which is red. The photochemical changes induced bv converged light 

 within the subsporangium induce swelling and eventual bursting at the tip. 

 The sporangium is carried away in toto with the squirt. (After Buller.) 



Later Parr (1918) concerned herself with precise measurements 

 of the responses of Pilobohis to wavelengths of the different re- 

 gions of the spectrum, to the presentation time, and to the energy 

 values involved. Her important conclusions include the follow- 

 ing: (1) Pilobohis responds phototropicallv to light in all re- 

 gions of the spectrum. ( 2 ) The presentation time required to 

 react phototropicallv increases gradually from the red rays to 

 the violet; that is, Pilobohis is more sensitive to violet than to red. 

 (3) The presentation time varies in inverse ratio to the square 

 root of the wave frequency. (4) For any given light source the 

 total energy value may be expressed as the product of the square 

 root of the wave frequency multiplied bv the presentation time. 



