PHYCOMYCETES 33 



the male cell being more active, and contributing to the more pas- 

 sive and receptive female cell which then matures the oosphere. 

 The fertihzation tube, present in all forms but Monohlepharis, 

 does not function as a conjugation tube. Instead of copulating 

 with the oogonium, it pierces the oogonial wall and penetrates 

 to the oosphere. Properly speaking, therefore, copulation 

 between the gametangia does not take place, and as they do not 

 merge to form a common cell their individuality is retained even 

 after fertilization. 



Contrasting in the higher Phycomycetes with oomycetous 

 reproduction is a wholly different type of sexuality termed 

 zygomycetous. It is present in many genera, and these con- 

 sidered as a group are called the Zygomycetes, In these forms 

 differentiation of the female gametangium to form oospheres 

 does not occur, and the end product of the sexual process is 

 termed the zygospore. The male and female gametangia are 

 usually morphologically identical, and are not designated by the 

 names antheridium and oogonium. In a few genera (e.g., 

 Zygorhynchus) they show a pronounced and constant difference 

 in size and shape, but the character of the sexual process is such 

 that the larger cell may not be regarded with certainty as the 

 female. Direct copulation of the gametangia takes place in all 

 cases, the contiguous walls of the two sexual organs are absorbed, 

 and a common cell results in which the two protoplasts are com- 

 pletely merged. In many genera the fusion cell then enlarges 

 and the individuahty of the copulating gametangia is completely 

 obliterated. In other cases only a pore is formed between the 

 two cells, and, though a fusion cell thus results, the identity of 

 the gametangia is retained. Finally, the fusion protoplast 

 rounds up, assumes a wall, and matures into the zygospore. In 

 some species one gametangium or the other forms the zygospore. 

 In others it fills the common cavity resulting from their complete 

 fusion. In still others it exists as a globose bud protruding from 

 one of the gametangia or from their point of union. It is not 

 clearly an endogenous spore. The gametangial wall enveloping 

 the fusion protoplast becomes greatly thickened and when thus 

 transformed serves as the wall of the spore. The zygospore 

 differs from the oospore is not lying free in the gametangium. 

 Fusion of one or more pairs of sexually different nuclei occurs 

 in the zygospore, nuclear conditions varying apparently in 

 different species. Functionally the zygospore corresponds with 



