LIFE HISTORIES OF FUNGI 265 



ago, when it was discovered that there are, in reality, two 

 unlike strains of Rhlzoptis-mycelmm, and therefore two 

 kinds of spores. The two kinds of mycelia are designated 



Fig. 191. — Petri-dish culture showing dark line of zygospores between 

 the (+) and ( — ) strains of a dioecious species of mo\d,'C/i(>anephora (Mc) 

 and white lines of "imperfect hybridization" between the strains of this 

 species and the opposite strains of JMucor V (Mv). Note the total absence 

 of zygospore formation between two (+) or two ( — ) strains. (After 

 Blakeslee.) 



as (+) and (— ). When the interminghng hyphae are of 

 h'ke strains, either all (+) or all ( — ), conjugation fails 

 completely, but when they are from unlike strains, zygo- 

 spores form in great abundance. This fact is strikingly 



