126 



EFFECTS OF RADIATION ON FUNGI 



presence of daylight, exposure for a single hour, even if followed 

 by return to the darkroom, being sufficient to result in the pro- 

 duction of pilei. Likewise in Lentinus lepideus [Buller (1905)] 

 the stimulus of light is necessary for formation of the pileus. 

 Fruiting bodies grown in weak light have grotesque shapes. Al- 

 though stipes are at first positively heliotropic and indifferent to 



Fig. 13. Petri-dish culture of Aspergillus clavatus in ordinary diffuse light. 



geotropism, by the time pilei begin to form they lose this reactiv- 

 ity to light, and negative geotropism dominates pilear develop- 

 ment. Aspergillus clavatus forms short conidiophores when 

 grown in total darkness, whereas conidiophores of two lengths, 

 one short and the other an inch or more long, are produced on 

 exposure to diffuse daylight [Wolf (1938)]. The colonies pro- 

 duced under these considerations might be suspected to belong 

 to two distinct species of Aspergillus. 



Psalliota campestr'is, the cultivated mushroom, when grown in 

 caves or cellars that are illuminated only to permit gathering the 

 crop, is completely indifferent to light. Many subterranean 

 fungi, as would be anticipated, are unaffected by light. Evidence 

 has accumulated, moreover, that a considerable number of slime 



