SEXUAL REPRODUCTION 



121 



The basis of present-day knowledge of sexuality in the i\lu- 

 corales was provided by the classical studies of Blakeslee (1904). 

 He determined that hvphal branches from the mycelium arising 

 from a single sporangiospore of some species interact to form 



Fig. 37. Sporodinia grandis. A. Sporangiophore bearing sporangia. 



(Adapted from de Bary.) B. Vertical section of sporangium; spores have 



been delimited by cleavage. (After Harper.) C, D, and E. Stages in 



zygote formation. (Adapted from Bainier.) F. Mature zygote. 



zygospores. He termed such species homothaUic. In other 

 species zygospores do not mature unless the interacting hyphae 

 arise from two sporangiospores of different potentialities. He 

 termed these species heterothallic. One of these thalli is func- 

 tionally female ( + ), and the other is functionally male ( — ). 

 Studies have shown that Sporodinia grandis, Absidia spinosa, 

 Dicranophora jidva, Rhizopiis sexiialis, Zygorhynchus spp., and 

 some species of Alucor belong to the homothallic group, whereas 



