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150 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 10 



the end of 3 weeks, pycnidia had formed in all the cultures in the 

 glass can but were less numerous than when similar cultures were 

 kept in daylight. No pycnidia developed in the cultures kept 

 in the card-board box. A few sclerotia-like bodies did form in 

 the moist cotton in the bottom of each tube, but these contained 

 no spores of any sort. The response of the cultures used in 

 this experiment to artificial light is like that observed by Coons 

 and Levin ('20). These workers induced pycnidial formation 

 by Plenodomus fuscomaculans and certain other light-sensitive 

 fungi by subjecting cultures on agar slants to radiation emanating 

 from two 100-watt nitrogen-filled electric bulbs. However, in 

 the experiment reported by the writer, the light used was of less 

 intensity and burned intermittently for only half the time. 



As a result of the experiments cited above, it seems clear that, 

 under ordinary cultural conditions, light is a necessary factor 

 for pycnidial production by Diaporthe Sojae. Its intensity may 

 be reduced to half or possibly less than half that of ordinary 

 daylight, and the duration of illumination need not be longer 

 than 6 hours. Moreover, electric light may be substituted for 

 daylight. On the substratum used no consistent differences 

 were observed between the amount of mycelium grown in 

 cultures in light and in darkness. In this respect, the writer's 

 observations differ from those of Coons ('16) and Harter ('17). 

 These workers report a more abundant production of mycelium 

 in darkness than in light. That light is only one of a number 

 of factors operating to induce pycnidial production is evident 

 from the writer's experience with cultures of the pod- and stem- 

 blight fungus on other substrata. Synthetic solutions and plant 

 decoctions solidified with agar give rise to very few, usually no, 

 pycnidia even when kept in strong diffuse light. 



Spore Germination 



Under suitable conditions, pycnospores begin to germinate 

 in 4 hours after being placed in tap water. The spores become 

 appreciably swollen by an intake of water and put out 1 or 2 

 slender hyaline germ tubes. At room temperature in summer, 

 the longest of these may reach in 18 hours a length several 

 times that of the spore. The tubes continue to grow for about 



