286 PROCEEDINGS OF THE AMERICAN ACADEMY. 



MUCOR III. 



The production of the zygospores of this undescribed Mucor, which 

 apparently belongs to the M. racemosus group, has been continued un- 

 der cultivation probably longer than those of any other heterothallic 

 form, with the exception of the " Harvard strain " of Rhizopus. 



The zygospores of this species were first found in a test-tube culture 

 infected by bacteria, which had been made from an impure transfer from 

 rat dung in an attempt to obtain an inconspicuous Mucor which was 

 concealed below the growth of what appeared to be a larger form. 

 Since it seemed not impossible that the production of zygospores might 

 in some way be connected with a change in the character of the sub- 

 stratum induced by the accompanying growth of bacteria, tests were 

 made by starting cultures from sporangial transfers to which bacteria 

 were added. The results of these cultures were, however, negative, 

 since no zygospores appeared. The original mixed culture was event- 

 ually freed from bacteria by successive mycelial transfers to solid media, 

 and continued to produce zygospores whenever masses of mycelia were 

 transferred from the zygosporic region. 



Similar experiments as to external conditions were carried on for 

 Mucor III, which have been already described for Rhizopus, but the 

 zygospores were more uncertain in their occurrence. In general, 

 nutrients with higher concentrations seem to support a greater abun- 

 dance of zygospores than those with lower concentrations. Few sub- 

 stances have been tested, but flour paste, plain bread and bread soaked 

 with dilate prune decoction, potato agar and potato agar plus 4 per cent 

 grape sugar, have all been successfully used as substrata for the j^i'oduc- 

 tion of zygospores. On plain agar, horse dung agar, and potato agar 

 acidulated with orange juice, however, it has not been possible to obtain 

 zygospores. 



When the cultures are grown in the warm oven at 26''-28^ C, the 

 formation of zygospores appears to be more abundant than when the 

 same substratum is used at the temperature of the laboratory. 



This species was finally resolved into its two sexual strains by making 

 separation cultures of zygosporic material which had been preserved in 

 a dried condition on bread. Five paired colonies were obtained separated 

 by zygosporic lines, and in all cases there was a more or less marked 

 difference apparent in habit of growth between members of each pair. 

 Later tests have shown that, in every instance, the cultures with the 

 lower development of sporangia have belonged to the strain which has 



