LIFE HISTORIES OF FUNGI 265 



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

 unlike strains of Rhizopus-mycelium, 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 mold, Choanephora (Me) 

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

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

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

 Blakeslee.) 



as (+) and ( ). When the intermingling hyphae are of 

 like 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 



