272 PROCEEDINGS OP THE AMERICAN ACADEMY. 



sporangial transfers taken from the edge of a zygosporic culture were 

 unsuccessful the reverse was true if similar transfers were taken from 

 the low growth in the centre of such a culture. 



Resolution of ( + ) and (— ) Strains. 



In order to discover whether tlie zygosporic activity could be trans- 

 mitted through the mycelium arising from any single spore, a separation 

 culture was made of a mixed sporangial transfer from this favorable 

 region in the centre of a culture which was producing zygospores in 

 abundance. This culture was made in three Petri dishes containing a 

 corresponding number of dilutions of the original transfer; and on 

 May 2 (1903) an examination of the dish containing the last dilution in 

 which but five colonies were present, showed the presence of certain 

 remarkable conditions which, by furnishing the first suggestion in re- 

 gard to what appear to be the fundamental causes affecting zygospore 

 production, have formed a basis for the gi-eater portion of the present 

 investigation. 



The conditions referred to are graphically illustrated in the accom- 

 panying diagram, in which the crosses indicate the centres of the mycelial 



colonies which had arisen from five 



©single spores. At the regions of con- 

 tact between certain of these colonies 

 a luxuriant formation of zygospores 

 was observed, as is indicated by con- 

 tinuous lines in the diagram, while 

 between others in the areas indicated 

 by dots no zj'gospores were formed. 

 It was soon demonstrated that in every 

 case the branches between which the 

 zygospores were borne could be traced 

 to the individual mycelia on either 

 side of these zygosporic lines just 

 mentioned. The apparent explanation of this unexpected phenomenon 

 was that in this species, or at least in the cultures from which this sep- 

 aration was made, the zygospores are developed through the interaction 

 of individual mycelia which are different in nature. 



To determine whether there were more than two distinct strains of 

 these different mycelia, other separations were made from various 

 zy'Tosporic cultures then in the laboratory, and pure cultures up to 

 eio'hteen in number were secured from the opposite sides of the several 



