236 THE LOWER FUNGI— PHYCOMYCETES 



upon. Teachers of botany desiring to use the common bread 

 mould in their laboratory work as illustrative of the Zygomycetes 

 were often at a loss to obtain zygospores, and subcultures from 

 zygospore producing material were in demand. Even these 

 frequently failed to develop zygospores. The spontaneous 

 appearance of zygospores on a variety of media and under widely 

 different conditions was wholly unexplained. 



The key to this mystery of zygospore production was dis- 

 covered by Blakeslee, and the explanation, though entirely 

 unexpected was very simple. Blakeslee (1904: 205) was working 

 on the problem of zygospore formation in Mucor mucedo and 

 obtained pure, zygospore producing cultures on agar. He found 

 that cultures from single sporangia of this material never pro- 

 duced zygospores, but that if a mass of mycelium was transferred, 

 zygospores appeared in abundance about the point of inoculation, 

 decreasing in number as the growth widened. It was found also 

 that mixed sporangial transfers from the center of the mass gave 

 origin to zygospores, while similar transfers from the margin of 

 the growth failed to do so. The culture which made clear the 

 fundamental nature of zygospore production was prepared in the 

 endeavor to discover whether the tendency to develop zygospores 

 could be transmitted through the mycelium derived from the 

 germination of a single sporangiospore. For this purpose dilution 

 cultures were made from mixed sporangial transfers from the 

 center of a zygospore group, one petri dish thus prepared contain- 

 ing only five spores. When the five mycelia which developed 

 from these spores met, it was seen that an abundant growth of 

 zygospores occurred along the line of apposition of certain of the 

 myceha, while between others none were formed. This culture 

 showed, moreover, that a given mycelium would produce zygo- 

 spores when meeting a second mycelium, and fail to do so on 

 meeting a third, which would form them on meeting the second. 

 Thus the culture indicated not only that two mycelia arising from 

 different spores are necessary for the production of zygospores, 

 but also that these spores are developed from the union of 

 mycelia which are different in nature. Blakeslee confirmed these 

 results by numerous observations on Mucor mucedo, and extended 

 his investigation to other members of the order. He found that 

 the majority of the Mucorales examined are of the type of Mucor 

 mucedo, and he designates these as heterothallic forms, because 

 two different thalli are necessary for zygospore formation. In 



