BLAKESLEE. — SEXUAL REPRODUCTION IN TUE MUCORINEAE. 239 



6, Fio-ure 9, the suspensors arise immediately uear each other from the 

 same mycelial branch; in other cases they are the ends of longer or 

 shorter hyphae whose insertions lie at a more or less considerable dis- 

 tance from each other and belong to altogether different systems of 

 branching." 



Although parasites caused the zygospore formation in this special 

 instance, Zopf thinks it must be possible to cause them by artificial means 

 without the parasites. He expresses his desire to discover the special 

 culture conditions necessary, but as nothing has been published on the 

 subject since, it may be assumed his investigations were fruitless. 



Were it not for Figure 9, we should consider the evidence of a hetero- 

 thallic condition very strong. The other twelve figures of zygospores, 

 however, illustrate rather the condition mentioned in which the progametes 

 belong to different systems. From the presence of Pleotrachelus and 

 Syncephalis in Zopf's zygosporic culture it is obvious that ho did not 

 have a pure culture of Pilobolus, and it is conceivable that an opposing 

 strain entered by the same road with the two parasites. His experiments 

 prove nothing, since in the second culture he did not introduce the para- 

 sites pure, but on fragments of the very dung that was producing zygo- 

 spore.^. If the form is heterothallic he transferred with the parasites the 

 mycelium of the two opposing strains. The account is strongly suggestive 

 of the writer's early work with Mucor in. (p. 286), the zygospores of 

 which first appeared in a tube culture infected with bacteria. 



Pilobolus Kleinii van Tieghem. 



In one of Zopf's ('92) cultures of P. Kleinii on sheep dung the forma- 

 tion of sporangia suddenly ceased, and all the sporangial primordia were 

 found converted into galls infected by the parasitic organism Pleotrachelus 

 fulgens. Since in dung cultures of the same Pilobolus where the para- 

 site was absent zygospores were not produced, Zopf concludes that as in 

 P. cryslallinus the suppression of sporangia by Pleotrachelus is the cause 

 of the zygospore formation. The figures are indecisive as regards the 

 origin of progametes. That the cause assigned by Zopf is not the true 

 explanation is evinced by the fact that Professor Thaxter has found the 

 zygospores of this species on sheep dung but without the parasite. In 

 preparations of this material which the writer has examined, the hyphae 

 in connection with the suspensors remain separate as far as it is possible 

 to follow them. 



