DIMORPHISM IN CONIOTHYRIUM PIRINUM SHELDON 455 
one of the plus colonies (Fig. ii). Progeny of this minus sector have 
bred true until the present time. 
These results indicate that the C. pirinum from the Bureau of 
Plant Industry was dimorphic in stock culture when received. The 
separation of the plus and minus forms was accomplished as in Strain 
I 0-0-0-\abwt2s[J 1-0-0=0-0-0-0-0=0=0-0-0-0-0-0-0-0-0-0-0 
e=e=©-e-e-e=e=©-e-©-e ®^ o-o-o-o 
J£ ®-@=®-\abdut7\}\-~^ 0=0-0-0-0-0-0-0 
0=0=0-0-0-0-0-0-0-0-0=0-0-0-0-0 
jiru-/" " '0-0-0-0 
\)-o=o-o-o-o-o-o-o 
©=©-e-©-©-©-©-©-©-©-©-© 
0=0-0-0-0-0-0 
Y U-o=o-o-o-o-o-o-o-o-o 
Fig. 6. Chart showing the history of 5 cultures of C. pirinum. 
O Petri dish culture of minus strain, 
e " " " " plus 
<8) " " " " mixed strains. It is in such plates that the plus and 
minus sectors have appeared. 
U Test tube culture. 
= Succeeding plates poured from spores of preceding culture. 
The plus strains suddenly give rise to minus strains which are subsequently 
constant generation after generation. It will be noticed that fewer generations of 
minus strains than plus strains have been grown in nearly every case. This is dua 
to the fact that the plus strains fruit more quickly than the minus strains and more 
generations can be produced in a given time. I and II were isolated by the writer, 
III (IV) and V by workers of the Bureau of Plant Industry. Subnumbered plates 
have been photographed. The numbers correspond with the numbers of figures 
appended. 
II. The minus form remained minus. The plus form threw off another 
minus form in the following 4th generation. 
On January 2, 1915, two other cultures of C. pirinum, B. P. I. 
227 and B. P. I. 345, were received from Dr. J. S. Cooley and desig- 
