454 
C. H. CRABILL 
the plus sectors of the same colony were typically plus and remained 
so for 5 generations when a third minus strain developed. 
Fig. 6 will show better than words the history of the development 
of these strains. 
On November 5, 1914, a culture of C. pirinum was received from 
Mr. J. W. Roberts, of the Bureau of Plant Industry at Washington. 
It was labeled III and immediately subjected to test to see if it would 
also develop plus and minus strains. 
Fig. 5. II + 2 and II — 2 of the same parentage as those in Fig. 4. These 
cultures are 8 days old. A single large pycnidium has developed at the point of 
inoculation in the II — 2 colony. When spores alone are transferred the formation 
of pycnidia begins much later. When mycelium is transferred as in the present 
case a few pycnidia often develop at an early age due to the fact that young pycnidia 
are sometimes transferred on the mycelium. These naturally hasten to maturity 
as soon as food is supplied. 
The first set of subcultures was made on Petri dishes of starch 
agar. Every colony showed fruiting and non-fruiting sectors (Fig. 7). 
Progeny of the minus sectors have remained constant, for 9 genera- 
tions or until the present time. Progeny of the plus strain remained 
constant only 4 generations, when a small minus sector appeared in 
