458 
C. H. CRABILL 
1. Mycelium was continuously selected from the extreme edge 
of plus colonies where no pycnidia were yet forming. 
2. Mycelium was continuously selected from colonies which were 
subjected to temperatures so low and so high that fruiting was poor. 
3. Mycelium was continuously selected from colonies grown in 
such dry atmosphere that fruiting was poor. 
Several generations of such selections gave no promise of the 
development of a minus strain. 
Attempts have also been made to develop a plus strain from a 
minus strain. 
Fig. 9. Same as Fig. 8, 16 days old. 
In all the minus strains studied there appear colonies which with 
age show greater prolificacy in some sectors than in others (Fig. 9). 
By the transplantation of spores only from the pycnidia of the pro- 
lific sectors generation after generation it was thought possible to 
build up a plus strain. Selection of this sort however has in no way 
altered the minus strain. Pedigreed cultures after such selection are 
in no respect different from pedigreed cultures obtained by con- 
tinuous selection of mycelium from the poorest fruiting sectors of 
the minus colonies. 
These experiments show that selection is not a factor in the origin 
