ENDOTHIA PARASITICA AND RELATED SPECIES. 43 



LIGHT RELATIONS. 



The relation of light to pycnospore production in Endothia para- 

 sitica was first discussed by Anderson (1, p. 20). He says — 



When plate cultures are grown in total darkness on chestnut-bark agar, no 

 pycnidia are developed, while on plates made at the same time and grown 

 in the light, the usual rings of pycnidia appear (fig. 57). Experiments were 

 also tried in which the plate was left in darkness until about half covered 

 with mycelium and then brought into the light. Circles of pycnidia were 

 developed, beginning with the ring which marked the outermost limit of the 

 colony when removed from the dark chamber. The concentric rings which 

 always appear on agar cultures are due to the alternation of night and day. 



Later, in a bulletin by Anderson and Eankin (6, p. 592), the same 

 results are attributed to D. C. Babcock. 



Up to the time the above-mentioned work was published the 

 writers had grown about 3,000 cultures of the several species of 

 Endothia on various media in flasks and tubes. Practically all of 

 these cultures had been kept in dark cases and Endothia parasitica 

 had produced pycnidia abundantly on most of the media used. It 

 seemed desirable, therefore, to determine whether wholly different 

 light relations existed when the fungus was grown on plates. The 

 following series of tests was accordingly made, using E. parasitica 

 only. 



LIGHT TESTS OF CULTTJEES ON PLATES. 



In experimenting with plate cultures in order to check up the 

 results reported by Anderson and Eankin (6, p. 592) it was noted 

 that there was great variation in the rate at which the cultures 

 dried out. There was considerable variation in this respect in dif- 

 ferent plates kept side by side, apparently due to differences in the 

 Petri dishes, and a marked difference between cultures kept in 

 light and those kept in darkness. Since a causal relation between 

 lack of moisture and abundant spore production had already been 

 shown, it seemed probable that this might influence the results of 

 the light tests in plate cultures. In fact, in a few cases the cultures 

 kept in the light did produce spores earlier than those kept in dark- 

 ness. Accordingly, in order to eliminate at least in part this fact 

 which seemed to obscure the possible effect of light, a method was 

 sought of equalizing the loss of moisture. In the following series 

 half the plates were placed under a plain bell jar and the other half 

 under a bell jar of equal size but darkened by being covered inside 

 and out with heavy black paper, such as is used to wrap photographic 

 plates. The two bell jars were then set side by side in front of a 

 north window. By this means the conditions were made much more 

 uniform as to temperature and moisture. There was still a slight 

 difference in the rate of drying and undoubtedly at times a difference 



