BLAKESLEE. — SEXUAL REPRODUCTION IX THE MUCORINEAE. 295 



the condition represented in Plate I, Figure 19, in which the zygophoric 

 hj'[)hae can be seen to have arisen in such a manner that there is an open 

 protoplasmic connection between the two progametes, and in this respect 

 the process is in marked contrast to that in Zygorhynchus, where the 

 more delicate zygophore is always normally distinguished at the end of 

 a filament by a septum below which the more vigorous zygophore arises 

 as a branch. That the zygophoric hyphae may be primarily bisexual 

 is suggested by the fact that, in one case observed, both of the zygophoric 

 hyphae connecting with a zygospore had grown on to produce sporan- 

 gia each of which we must assume contained bisexual spores. It is 

 possible that the segregation may be partial in the zygophoric hyphae, 

 giving to one a predominatingly (+) character and to the other, with 

 which it forms progametes, a predominatingly ( — ) character. So far as 

 they have been investigated, however, the mycelia developed from single 

 spores are always equivalent as regards their sexual character. Separa- 

 tion cultures have been made both from transfers from single sporangia 

 and from mixed transfers from a number of sporangia, and no difference 

 could be observed in the zygosporic production of the different mycelial 

 '•'colonies " developed, nor was there a line of greater z3'gosporic activity 

 where the mycelia of two colonies came in contact. It is perhaps fruit- 

 less to speculate on these questions without more data than are at present 

 available ; but the writer hopes in the near future to be able to present 

 additional experimental evidence bearing on the subject. 



Homothallisra appears to be a fixed condition in the species in which 

 it has been found. During the six years Mucor ii has been under cul- 

 tivation in the laboratory, it has been continued to many generations of 

 sporangial spores without suffering any abatement in its zygosporic 

 activity, and the same is true, though to a less extent, of the other forms 

 of the homothallic group. The thallic character, moreover, is not lost 

 through the production or germination of zygospores, since although in 

 water germinating zygospores produce only sporangia, in nutrients their 

 germination gives rise to a mycelium from which are formed both zygo- 

 spores and sporangia. 



Since Mucor i was the first homothallic form that the writer had 

 found and brought under cultivation, it has been the subject of a consid- 

 erable number of cultural experiments, the object of which was to dis- 

 cover if possible the factors influencing the formation of zygospores 

 in this species, as Klebs had done in Sporodinia, and to apply the results 

 obtained in an attempt to secure zygospores in other forms. In these 

 cultural investigations nearly two hundred pure gross cultures and some- 



