BLAKESLEE. SEXUAL HErilODUCTION IN THE MUCORINEAE. 279 



the mycelial transfers grew vigorously. While, however, the (+) tubes 

 remained unatft-cted the growth in the (— ) tubes gradually became again 

 • weaker until February 15, when the mycelium in tube B(— )oi was 

 almost at a standstill and did not develop sufficiently for a transfer 

 until two days later. The (— ) series was then continued on potato agar 

 to which four per cent grape sugar had been added, but the increased 

 nutriment was not a sulRcient stimulus to carry tlie growth well beyond 

 the sixty-fourth generation, when, on February 19, the series was discon- 

 tinued. The (+) series had then reached the seventy-second generation, 

 and to all appearances had been unchanged either in vegetative or sexual 

 vigor. On the other hand it was ten days before tul)e B( — )c4 had devel- 

 oped sulficiently for the formation of sporangia and transfers, made from 

 its spores, in contact with (+) inoculations produced but a feeble my- 

 celium which was unable to take part in the production of zygospores. 

 The same was true of a similar contrast made March 8, but when the 

 experiment was repeated March 13, the growth was better, and a line 

 of zygospores, though somewhat scanty, resulted. From an earlier 

 sporaugial culture made from the tube B( — )g^ zygospore? could be ob- 

 tained by contrast against (+) strains, and it is possible that some of 

 the spores of the March 13th transfer were derived from a mycelium 

 ■which had developed as a result of a resowing of the tube by the first 

 stunted sporangia formed. 



Tlie experiment demonstrates that the continuous cidtivation of the 

 mycelium, in so far as conducted, has no apparent influence on the 

 vegetative vigor nor on the sexual capacity of the (+) strain, while it 

 decreases to a marked degree the vegetative vigor, and, as a consequence, 

 the sexual capacity of the ( — ) strain. The sexual character is not, how- 

 ever, lost, but is merely unable to exert itself when the vital force in the 

 mycelium is thus reduced. The series further offers another example of 

 the general law that unfavorable conditions inhibit the formation of zygo- 

 spores before that of sporangia. 



Germination of Zygospores. 



Mucor Mucedo is the only heterothallic species the zygospores of which 

 the writer has succeeded in germinating. In April, 1903, a number of 

 washed zygospores which had been taken from a tube culture of the 

 previous February were sown in a van Tieghem cell. When they were 

 for the last time inspected in the following June, no apparent change had 

 taken place in them, but in October, when the cell was re-examined, it 

 was found that zygospores had germinated and pushed their sporangio- 



