BLAKESLEE. — SEXUAL REPRODUCTION IN THE MUCORINEAE. 219 



writer's opinion, due to the fact that their experimentation has been 

 based on the erroneous assumption that external conditions were the 

 controllins factors in the problem, whereas they are in reality either 

 wholly witiiout inlluence or of quite secondary importance. 



In regard to the significance of the phenomena of conjugation it may 

 be said that although from the time of Ehrenberg ('20), the union of 

 gametes has been generally held to represent a primitive sexual process, 

 there have been some who see in this fusion only a vegetative process. 

 Vuillemin ('87) at some length maintains that in his Zygorhynchus 

 heterogamus the inequality of the gametes, which he homologizes with, 

 sporangia, is due to differences of alimentation and is of no sexual, 

 significance. This union he compares to the anastomosis between 

 mycelial cells commonly seen in the clamp connections of the Basidiomy- 

 cetes, and from the absence in the formation of zygospores of characters, 

 which are supposed to be essential to a sexual process he casts doubt 

 on the presence of sexuality in the whole group. Brefeld, though oppos- 

 ing the majority of mycologists in denying sexuality to the Ascomy- 

 cetes, speaks throughout of the formation of zygospores as a sexual 

 process. Van Tieghem even goes so far as to find an indication of' 

 sexual differentiation in the size of the gametes in Rhizopus and Pilaira 

 ('75, p. 81), and in the fact that the forked spines of the zygospores of 

 Phycomyces ('73, p. 295) are produced from one suspensor before they 

 are from the other. Klebs ('98), in his paper on Sporodinia, although 

 recognizing sexuality in the formation of zygospores, does not discuss 

 the subject, and investigates the production of zygospores on the same 

 basis as he would that of any other reproductive form of a polymorphic 

 fungus. Falck ('01, p. 302) merely mentions in a footnote the word 

 "sexuality," and then says that the process of conjugation can be also 

 explained on the basis of mechanical forces, and that the azygospores can 

 as well be sexual. 



In regard to the cytology of the zygospore there is little decisive 

 knowledge. The zygote is at first multinucleate, but, according to Leger 

 ('96), with the accumulation of oil in the centre the nuclei entirely dis- 

 appear, and at opposite poles of the zygospore appear two groups of 

 small granular bodies which are called " Spheres embryogenes." Those 

 in each group fuse together, and the two thick-walled bodies thus formed 

 are the "Spheres embryonnaires " which are to be found in mature 

 zygospores of all the Mucorineae. At germination the " Spheres 

 embryonnaires" increase in size, lose their walls, and fuse with each 

 other. The nuclei which now reappear undergo one mitotic division and 



