314 



PHYSIOLOGY OF THE FUNGI 



For these chemicals to stimulate pycnidium formation, the culture had 

 to be in such a physiological condition that 1-hr. exposure to light would 

 induce sporulation. 



The sporulation of a number of other species in our laboratory has been 

 observed to be influenced by the presence or absence of light (Figs. 60, 

 61). Among these are Dendrophoma obscurans, Trichoderma lignorum, 



Fig. 60. The effects of light on the 

 production of conidia by Trichoderma 

 lignorum after 3 days at 25°C. A, 

 exposed to continuous artificial light. 

 Note the more or less even distribution 

 of conidia. B, exposed to alternate 

 ight and darkness, 12 hr. each. Note 

 the rings of conidia. C, grown in 

 continuous darkness. Note the ab- 

 sence of conidia. 



Sphaeropsis malorum, Ceratostomella ulmi, Botrytis sp., Endothia para- 

 sitica, Septoria nodorum. The reaction of some fungi to light is appar- 

 ently dependent, to a certain extent, upon the composition of the medium. 



Still another effect of light should be emphasized, i.e., the inhibitory 

 effect. The depressing effect of strong light upon growth and length of 

 sporangiophores of Phy corny ces hlakesleeanus is easily demonstrated. 

 Elfving (1890) noted that the amount of inhibition of growth by light 

 varied with the composition of the medium. 



Ultraviolet light. The destructive action of sunlight upon micro- 

 organisms, especially bacteria, was recognized about the time that pure- 



