262 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Other culture at least of the Rhizopus material which has been seut to 

 the laboratory. 



The fact that in the Chicago culture the strain remaining has (+) 

 characters, while in the culture in the Harvard laboratory the strain 

 remaining has (— ) qualities, shows that the running out of these scions 

 of the original Harvard zygosporic culture is probably due to accidental 

 circumstances accompanying the gross transfers of their spores or to con- 

 tamination from outside strains. The method of perpetuating these 

 zygosporic strains in gross cultures for class work is such that there 

 is no assurance that the culture at the end of the series has any genetic 

 connection with the one at the beginning. Comparatively little can 

 be learned, therefore, from a study of what remains from the " Harvard 

 strain." 



Distribution and Thallic Character of Strains in Nature. 



The existence of (+) and (— ) strains in Rhizopus having been defi- 

 nitely established, it seemed desirable, owing to the ease with which this 

 very common form may be obtained from distant sources, to test its 

 thallic character by a detailed examination of as many and as varied 

 cultures as could be procured, and with this object in view material was 

 collected from various sources and tested in detail, with the results 

 hereafter enumerated. 



Associations of (+) and (— ) strains of this species have been found 

 producing zygospores in Germany, and France, and have been obtained 

 by the writer from diverse parts of this country, and investigated, with 

 the results set forth in the previous pages. Accordingly questions now 

 arise in regard to the distribution of the individual strains. Requests 

 have been sent to a number of botanists in different parts of this and 

 other countries for spore material from their localities, together with 

 suggestions for obtaining the fungus on spontaneous cultures of bread. 

 Thanks to the kindness of the writer's correspondents, he is able to 

 represent by means of Table X the results obtained by the cultivation 

 of material from a wide range of territory. In cases wliere more than 

 a single contribution was received from a given locality the material 

 was of different origin, and in the table numerals indicate the order in 

 which the tests were made. 



Nearly all the material was received in a dried condition, generally on 

 bread, and inoculations were made into acidulated agar tubes in the 

 writer's lodging where danger of contamination from the laboratory 

 spores was minimized. When the cultures had been freed from the 



