

the outer margin of the mycelial mats in this study they could 

 not he separated from what appeared to he internal changed in 

 the fungus itself. This consideration will become clearer 

 in the sequal. 



Since the elongating hypae of the fungi lie largely 

 near the aerial surface of the agar plate, while some are 

 partially in contact with the air-space above, it is neces- 

 sary to consider the aerial environmental conditions, as well 

 as those within the agar medium itself. Aside from temper- 

 ature, the air conditions in the culture di3hes above the 

 agar were sensibly the same in all cultures at the start, 

 excepting that the vapor tension of the water was , of course, 

 different for cultures exposed to different temperatures. 

 The air-space of the culture dish was always practically 

 saturated with water vapor. But the culture dishes could 

 not be hermetically sealed because it was desired to main- 

 tain practically unchanged the original oxygen and carbon 

 dioxide concentrations in and about the agar. This, of 

 course, allowed to take place a slow escape of water vapor 

 from the dishes and consequently a slow evaporation from the 

 agar surfaces during the culture period, the rate being some- 

 what greater at higher than at lower temperatures. The con- 

 sideration just mentioned shows that the conditions of the 

 medium were not strictly maintained throughout the culture 

 period, but that different maintained temperatures were auto- 

 matically accompanied by different rates of variation in the 

 water content of the yet unoccupied medium. Such variation, 



14 



