DIMORPHISM IN CONIOTHYRIUM PIRINUM SHELDON 453 
of pycnidia and spores produced by the plus strain, the proHficacy of 
the minus strain falls into insignificance. 
To test out the evidence that a minus strain had split off from a 
plus parent, dilution plates were poured, using spores from both the 
plus and minus strains. All the progeny of the plus strain were 
typically plus. All the progeny of the minus strain were typically 
minus (Figs. 4 and 5). The former produced abundant pycnidia and 
Fig. 4. Second dilution plates poured from the colonies shown in Fig. 3. 
These plates are 5 days old and of the second generation after the mutation. They 
therefore have the labels II + 2 and II — 2. 
Note: Wherever two or more cultures appear in the same figure they were 
inoculated at the same time, incubated the same time under the same belljar, and 
photographed on the same plate. 
fruited in 4 days. The latter fruited sparingly only after 14 days. 
Spores from these dilution cultures were used to pour other plates. 
Again all progeny of plus parents were typically plus and all progeny 
of minus parents typically minus. For 12 generations the plus 
strain remained entirely plus. Then suddenly it gave rise to a minus 
sector in a petri dish culture. The progeny of this sector were typic- 
ally minus, whether poured or transferred by wire. The progeny of 
