130 



EFFECTS OF RADIATION OX FUNGI 



rates of growth on opposite sides of the growing zone. This ex- 

 planation is not entirely satisfactory if it is borne in mind that 

 the sporangiophores are radially symmetrical and that the regions 

 of sensitivity and of growth coincide. 



4 



Fig. 16. Response of Phycomyces to incident light. In A, grown in air, 

 the sporangiophores bend to direct the sporangia toward the light. In B, 

 the sporangia are surrounded with paraffin oil and have turned away from 

 the source of light. Density of the surrounding medium conditions the 



(After Buder.) 



direction of refraction of light. 



Further evidence to clarify this problem was presented by 

 Buder (1918). He grew P. nit ens, with the sporangiophores di- 

 rected vertically, in chambers whose vertical sides were parallel. 

 He then immersed the sporangiophores in one chamber in paraf- 

 fine oil; in the control chamber the sporangiophores were sur- 

 rounded by air. Illuminating both unilaterally, he found that 

 those in oil were negatively phototropic, whereas those in air 

 were positively phototropic. In explanation Buder pointed out 



