120 



SCIENCE. 



[N. S. Vol. XXIV. No. 604. 



INDIVIDUAX STEAINS ABEANGED ACCOBDING TO SEXUAL CHABACTEB. 



TABLE III. 



LIST OF SPECIES, THE THALLIC CONDITION OF WHICH HAS BEEN DETEBMINED, AB- 

 BANGED ACCOBDING TO THE TYPE OF THEIE SEXUAL EEPBODUCTION. 



In Table III,, which contains the species 

 investigated by the writer, arranged according 

 to their thallic character, the figures opposite 

 the heterothallic forms indicate the number 

 of different (-h), ( — ) and neutral strains 

 which have been tested of these species. In 

 addition the writer has a considerable number 

 of cultures which the hybridization reaction 

 would indicate are unmated strains of hetero- 

 thallic species. 



The sexual character of individual strains 

 of all the heterothallic species investigated 

 has remained unaffected when they are culti- 

 vated vegetatively. Thus the (+) and ( — ) 

 strains of Phycomyces and Miocor Mucedo 

 have been cultivated separately for 92 and 90 

 sporangiospore generations, respectively, and 

 are as active sexually as when their zygo- 

 spores were first discovered. Moreover, the 

 two opposite strains of Rhizopus have by daily 



transfers of mycelia been brought to the 

 seventieth generation and by transfers of spo- 

 rangiospores to the thirtieth generation with- 

 out the production of zygospores; yet it is 

 only necessary to make sowings together on 

 the proper substratum of spores from the 

 (+) and ( — ) tubes at the end of the series 

 in order to obtain zygospores in abundance. 

 The homothallic species have also been culti- 

 vated to many non-sexual generations, some of 

 them for ten years and over, without change 

 in their sexual behavior. Homothallism and 

 heterothallism therefore seem to be fixed con- 

 ditions in the forms in which the sexual char- 

 acter has been determined. 



In view of the facts summarized, it would 

 seem probable that Mr. Hamaker had been 

 working with impure cultures rather than 

 that he had discovered a new homothallic 

 species of Rhizopus. This is further sug- 



