136 



EFFECTS OF RADIATION ON FUNGI 



raphyses are positively phototropic. Since its hymenial surface is 

 hemispherical, the amount of bending of the ascus tip is related 

 to the position of the ascus. Asci near the center are straight, 

 whereas those near the periphery may be bent through an anp;le 

 of 45°. In Morchella cornea, M. crassipes, and Ptyc hover pa 

 (Verpa) bohem'ica the fertile portions of the fruit bodies may be 

 regarded as compound disks. The asci are phototropic and be- 

 have as though each alveolus were a disk. The stipes of some of 



12 M. 6 P.M. 



12 P.M. 



6 A.M. 



12 M. 



6 P.M. 



Fig. 19. Diurnal cycle of development of asci by Tctphrina deformans. 



(After Yarwood.) 



these stalked species bend in response to light, thus carrying the 

 fertile tissues into the position most favorable for ascospore dis- 

 charge and dissemination. 



A diurnal rhythm in the discharge of ascospores is known to 

 exist in certain species. Ingold (1939) observed that Hy poxy Ion 

 jusciim discharges its spores nightly during the approximate pe- 

 riod between 9 p.m. and 5 a.m. In Nectria cimiabarina and 

 Podospora curvula, however, ascospore discharge occurs in the 

 daytime. 



By direct microscopic examination and by use of spore traps, 

 Yarwood (1941) found that in Taphrina deformans the ascoge- 

 nous cells give rise to asci in the evening and that nuclear division 

 and increase in size of asci occur throughout the night. During 

 the following daylight period the ascospores become morpho- 

 logically mature, and maximum discharge occurs during the early 

 portion of the succeeding night. This rhythm is attributed to 

 alternating light and darkness, but the significant effect of light 



