310 PROCEEDINGS OF THE AMERICAN ACADEMY. 



branched, and, although generally sterile, cases have been observed in 

 which sporangia have been produced from them. Sporangia, however, 

 have never been found in direct connection with the convoluted hyphae 

 of Phycomyces. The branches of 3f. Miicedo may be distinguished from 

 those of Phycomyces by the fact that the walls of the former are cov- 

 ered with granulations, while those of the latter are smooth. 



Miicor Macedo does not as readily hybridize as some of the other 

 forms ; with Mucor vi, its sexual action is at best feeble, and often there 

 is no response observable ; and with Absidia and with Mucor iii, al- 

 though tests have been made, no hybrids have been obtained. The (+) 

 strain of M. Mucedo, after having been rendered neutral towards its (— ) 

 strain by cultivation (p. 277), has been found no longer to form hybrids 

 with var. A. This further emphasizes the conclusion that the stimulus 

 for the production of progametes is the same in the formation both of 

 hybrids and of zygospores. 



As has been already mentioned, Mucor v is more active in forming 

 hybrids than any of the other heterothallic forms known, and the strains 

 of none of them have failed to respond when a contact with the proper 

 strain of this species has been offered. For this reason Mucor v has 

 been used in the few tests that have been made to determine the thallic 

 condition of species the (+) and (— ) strains of which have not been 

 differentiated. They have been listed in Table XII (p. 305) under the 

 sign opposite that of the strain to which they show a sexual response. 



The zygospores of Circinella umbeUata have been reported only by 

 Bainier ('03), and in his figure he has represented a zygospore with its 

 two suspensors in connection with the same hypha. Such a condition 

 would indicate that the species is homothallic, but the evidence from hy- 

 bridization points to a contrary conclusion. 



Cultures of a new species of Chaetocladium, found by the writer in 

 Venezuela, which can be readily grown saprophytically, and of Synce- 

 plialastrum, hybridize with Mucor v (-f), and it is thereby rendered 

 probable that these as well as some other species of the genus Mucor 

 tested are individual (— ) strains of heterothallic forms. 



Cultures of C imninghamella echimdata, a species originally described 

 by Thaxter ('91) under Oedocephalum and recently redescribed as C. 

 Afnca/ia by Matruchot ('03), who referred it to the Mucorineae largely 

 on the ground that it acts as a host for Piptocephalis, have responded 

 to the hybridization test with Mucor v (— ), and have thus been 

 shown to be (+) in character. In so far as may be determined, there- 

 fore, by the presence of a sexual response, the conclusion of Matruchot 



