280 PROCEEDINGS OF THE AMKPJCAN ACADEMY. 



phores down into the water below, but no growth from any sporangial 

 spores was observed. Transfers from this culture were made into three 

 agar tubes, but in only one of them was there any mycelial growth, and. 

 in this single case it was accompanied by bacteria probably derived from 

 the water in the bottom of the van Tieghem cell. By a single sporangial 

 transfer a pure tube culture, however, was obtained from this infected 

 growth, and tests to determine its thalUc condition were made during 

 October with five (4-) and six (— ) cultures, but with negative results. 

 Subsequent tests were made in January of this same tube and of later 

 members of a series of which this tube was the first. All were decidedly 

 (— ) in character except the most recent cultures in the series, which 

 appeared to be neutral. 



In so far as can be ascertained from the behavior of the cultures in a 

 single experiment of this nature, one may infer that the zygospores from 

 which the series was derived had, in germinating, produced spores, in the 

 mycelium arising from which, the sexual character was dormant, but that 

 the capacity for conjugation became evident after a certain lapse of time. 

 The experiment is unsatisfactory in that the origin of the cultures can- 

 not be traced with absolute certainty to an individual zygospore, although 

 there is not much doubt that they were thus derived. A determination 

 of the time at which the segregation of the sexual characters occurs in 

 strains derived from zygospore germinations, and the nuclear condition 

 associated with it, is a matter of considerable interest. The writer hopes 

 soon to be able to present more satisfactory evidence bearing on the 

 question, and until a greater body of facts is known it will not be prudent 

 to attempt any general discussion of the subject. 



Differentiation between the (+) and (— ) Strains. 



The (+) and (— ) strains of this species offer no morphological dif- 

 ferences by which as yet they can be distinguished. In the conjugative 

 apparatus certain differences may exist in the size and time of appear- 

 ance of the gametes, in the size of the mature suspeusors, or in the 

 length of the zygophoric branches, but none of these characters have 

 been found to be correlated with the sexual differentiation of the strains. 

 The shape and size of their spores and their gross appearance in pure 

 cultures are essentially alike in both instances. Although no morplio- 

 logical difference has been determined, yet, as has been shown by the 

 more rapid attenuation of the ( — ) strain when the two were grown 

 at an unfavorable temperature and by the cessation of growth in the 

 same strain in the mycelial series when the (-f) was unaffected, there 



