48 Forest Club Annual 



ilar moisture and temperature conditions, produced five crops of 

 conidial threads from the same pycnidia within six months. Be- 

 tween experiments the threads of spores were washed off with 

 distilled water and the specimen subjected to a temperature ot 

 115 C. for one minute. 



The effect of light on the rate of growth was also studied. 

 Cultures of the fungus were grown in absolute darkness and in 

 bright daylight. Eight days after inoculation, pycnidia had form- 

 ed on the cultures kept in the dark as well as on those kept in 

 the light. Fewer and slightly smaller pycnidia had formed in 

 the dark than in the light. The yellow color of the mycelium was 

 the same in both cases. 



The effect of light on the shape of the fruiting body is mark- 

 ed. When the fungus is grown in the shade, the necks of the 

 perithecia lengthen perceptibly, while the perithecia themselves 

 often form entirely above the bark in the stromatic tissue de- 

 veloped there, thus giving rise to abnormal pustules. Pycnidia 

 also respond to this stimulus. The pustules containing them, when 

 found in a shaded position, generally show slightly erumpent 

 necks. 



Conditions Under Which Ascospores Are Discharged From 



Perithecia. 



As stated above, the ascospores are contained in the asci 

 within the perithecium. If these spores remained within the peri- 

 thecium, infection from this source would be slight. On the 

 contrary they are not retained within the perithecium except in- 

 dry weather. After a rain these spores shoot into the air in 

 countless numbers. When the walls of the perithecium become 

 wet they swell and this results in a diminution in the size of the 

 perithecial chamber. This contraction causes the ascospores to 

 be forcibly ejected through the ostiole. This is. not merely a push- 

 ing out en masse as is the case with the conidia, which are pushed 

 out in a gelatinous string, but the ascospores come out singly and 

 do not have a tendency to adhere to each other. To substantiate 

 this observation an experiment was performed in which bark 

 containing perithecia was moistened with water. After the asco- 

 spores began to shoot, air was forced over the discharging peri- 

 thecia. Slides were exposed to catch the ascospores. These slides 

 when examined under the microscope showed that the ascospores 

 were scattered and not adhering in masses like conidia in the 

 "spore horns". Investigations indicated that there was practically 

 no expulsion of ascospores during the winter months. 



Mature perithecia were observed to commence discharging 



