204 Transactions British Mycological Society. 



oxygen and moisture is also shown in the field by the fact that 

 the fungi attack their hosts preferably at the ground level where 

 both factors are most suitably balanced. The foregoing table 

 gives the macroscopic characters of the forms when grown on 

 the freshly made media which proved to be most suitable for 

 growth and diagnostic characters*. The descriptions refer to 

 cultures about one month old. All with the exception of B 

 produce in the first week a fair amount of aerial growth which 

 collapses when the medium begins to lose its moisture. The 

 column "Aerial growth" in the table refers to that which is 

 present when the culture is one month old or more. 



From the above it will be seen that I, A, B, and W, can be 

 easily distinguished by their mode of growth, and with practice 

 E can also be distinguished from all others by a characteristic 

 slaty-grey colour of the surface of the sclerotia on potato. On 

 agar the latter can be distinguished by the large number of 

 small sclerotia (about i mm. in diam.) formed on sides of tubes 

 and by the fact that the mycelium covers the surface of both 

 media with a felt of growth resembling that of B. 



Temperature and Rate of Growth. A comparison between the 

 rates of growth were made by measurements and observations 

 on several cultures on different media at temperatures of o-i° C, 

 5-8° C, 21-23° C. The manner of subculturing, although done 

 as uniformly as possible, did not always give the same results. 

 In a number of subcultures of any one form some commenced 

 growth quicker than others and any slight difference in the 

 moisture content of the medium or air in the tube or Petri dish 

 made an appreciable difference in the rate of growth. For 

 comparing the rate of growth at the above temperatures sub- 

 cultures of all forms were made at the same time from young 

 rapidly growing cultures of the same age incubated at 21-23° C. 

 and immediately placed in chambers and kept there for five 

 days. At temperatures 0-1° C. none of the fungi made any 

 growth whatsoever. At 5-8° C, E, I and B made no growth. 

 The disc of growth of W measured 5 mm. in diameter and for 

 5, A, PO and PE growth ranged from 20-22 mm. in diameter. 

 On placing the cultures kept for five days at the lower tempera- 

 tures in an oven at 21-23° C, growth took place within twenty- 

 four hours and continued as usual. At 21-23° C. the fungi can 



* These were steamed potato and malt extract agar prepared as follows: 

 Steamed potato (P) potato cut into wedge-shaped pieces, placed on moistened 

 cotton-wool at the bottom of large tubes and sterilised by steaming. Malt 

 extract agar (M), 200 grs. crushed barley to 1000 c.c. of distilled water at 45° C. 

 Kept at 45° C. for half an hour, then temperature raised to 70° C. in half an hour. 

 Kept at 70° C. for one hour and filtered. Distilled water added to s.G. 1-020. 

 Then 3 per cent, of agar added, autoclaved, cooled and egg albumen added. 

 Autoclaved, filtered, tubed and finally autoclaved. 



