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C. H. CRABILL 
nated IV and V respectively. The latter, B. P. I. 345, was isolated 
by Dr. Cooley from a soft rot of apple on December 3, 1914. The 
behavior of these cultures is shown in the diagram. Very likely IV 
is of the same parentage as III, received from Mr. Roberts of the 
same laboratory. The first subcultures showed it to be dimorphic, 
i. e., producing plus and minus sectors (Fig. 12). 
The first subcultures of V (B. P. I. 345) showed it to be a minus 
strain (Fig. 12), and it has so remained for 10 generations as shown 
in the diagram. It is identical with Strain I and with all the other 
minus strains developed in culture. 
Fig. 7. C. pirinum III. First subculture. 19 days old. Plus and minus 
sectors were more numerous in these cultures than in any previously or subsequently 
examined. These plates were opened for examination five days previous to photo- 
graphing, hence the contaminations around the edges of the cultures. 
The plus strains are all identical in appearance and behavior. 
The fact that the minus strain of C. pirinum, viz., I and V, and the 
plus strain, viz., II and III (IV), have been twice isolated by investi- 
gators working separately indicates that plus and minus strains exist 
in nature. 
The cultural studies show that minus strains may arise from 
plus strains by a sudden sporting or mutation. An objection might 
