278 PROCEEDINGS OP THE AMERICAN ACADEMY. 



the normal strains had also done, that these two later generations of the 

 (— ) strain had lost their sexual character before those of the (+) strain. 

 It is apparent that the final disappearance of the ( — ) characters occurred 

 at or before the time of sporangial formation in tube A( — j. while tlie dis- 

 appearance of the (+) characters occurred at or before their formation 

 in tube A(+)6> or iu other words the attenuation of the ( — ) strain took 

 phxce tliree generations before that of the (+) strain under like conditions 

 of cultivation. It remains to be seen whether, along with the disappear- 

 ance of their power of conjugation the (+) and (— ) characters of the two 

 strains have been entirely lost beyond the possibility of being regained 

 by a continuation of the series under more favorable conditions. 



The temperature of about 80° F. at which the above series was con- 

 ducted is not at all unusual during summer months, and an attenuation 

 of a double series of (+) and ( — ) strains which was carried on during 

 the spring and autumn may be accounted for by the unfavorable effects 

 which the warm weather occurring at that time might have exercised on 

 their growths. That the mere number of sporangial generations, how- 

 ever, through which the strains are conducted has little influence on their 

 sexual power is shown by the unchanged sexual nature in a double spo- 

 rangial series of the (+) and ( — ) strains carried on during the winter, 

 the one to the tenth, the other to the eighteenth generations. 



In order to discover to what extent the growth of the fungus could be 

 continued by mycelial transfers alone, and to observe the effect of such 

 treatment on the (+) and (— ) strains, transfers were made, December 

 11, into tubes B(+)i and B(— )i and formed the starting points for a 

 mycelial series of tube cultures such as was begun on the same date for 

 Rhizopus and has already been described (p. 265). Each morning a 

 piece of the nutrient agar with the mycelium adherent was transferred to 

 a new tube, and the series was continued in this manner, with no percep- 

 tible difference in the growths of the two strains, until about the twentieth 

 generation, when, while the (+) mycelium remained normal, the activity 

 of the ( — ) appeared to be checked, and, on January 5, the mycelium of 

 B( — )25 had developed scarcely sufficient growth to enable a transfer 

 to be made, and for several days thereafter underwent but little increase. 

 Eventually, however, this tube produced sporangia, and when tested a 

 month later showed by forming zygospores in contact with a (+) strain 

 that its sexual character had not disappeared. 



The growth of the ( — ) series was renewed by taking a mycelial trans- 

 fer from tube B( — )23 from the upper part of the tube where a mycelium 

 had evidently been developed from fallen sporangia, and for some time 



