DIMORPHISM IN CONIOTHYRIUM PIRINUM SHELDON 46I 
evidence points to the conclusion that the variation which gives rise 
to minus strains occurs in the spore rather than in the myceHum which 
develops from it. 
The study of plants of C. pirinum on Petri dishes shows beyond a 
doubt that the fungus is chemo tactic, i. e., growing only in the direc- 
tion of its food supply or that it produces some toxic substance detri- 
mental to its own growth. 
Whichever the case may be, two plants in close proximity never 
grow entirely together (Fig. 13). The mycelial threads of the two 
do not interlace. They are to that extent antagonistic. 
Fig. 12. IV and V, respectively. First sub-cultures, 24 days old. 
Some simple tests indicate that this apparent antagonism, is not 
due to excreted toxins. The fungus was grown for two months on a 
liquid medium containing starch. This medium was then filtered 
through a sterilized Chamberland filter. 
The extract, which was found sterile on plating, was used as 
follows : 
1. A large drop of the plain extract was placed at the margin of 
a thrifty colony on each of several Petri dishes. 
2. Boiled extract was used in a Uke manner. 
3. Plates were poured with plain extract and cooled agar and 
subsequently inoculated. 
