﻿328 BOTANICAL GAZETTE [may 



of gametangia. But it is important that we should recognize 

 this condition among the Ascomycetes as one that further study 

 may show to be not uncommon in the group. Juel (1902) 

 reports it for Dipodascus. Miss Nichols's (1896) studies on 

 Ceratostoma, while inconclusive in cytological details, are of 

 importance in this connection. She has described and figured 

 multinucleate oogonia (archicarps) and antheridia, which are 

 said to fuse. They are apparently coenogametes, and it is 

 probable that these structures will be found in other genera of 

 the Pyrenomycetes and Discomycetes, There are several forms 

 whose archicarps suggest a coenocytic structure (Eremascus, 

 Ascobolus, Sordaria, Eurotium, etc.). 



The student of the homologies and evolution of the sexual 

 organs among the Ascomycetes now finds himself face to face 

 with the same problem that has been presented to Stevens and 

 myself for the Phycomycetes. What is the relation of the uninu- 

 cleate gamete (^. ^., Sphaerotheca) to the multinucleate ? Which 

 condition is the more primitive? 



There is likely to be some confusion of homologies among 

 the sexual organs of the Ascomycetes. The oogonium (archi- 

 carp) of Sphaerotheca is morphologically a* gametangium, and 

 so is the antheridium, but both structures are physiologically 

 gametes. The oogonium and antheridium of Pyronema are 

 morphologically gametangia, so that in comparing these two 

 forms we are dealing with homologous structures. Of course, 

 we use them merely as illustrating certain sexual conditions ; 

 indeed, they are almost the only Ascomycetes whose sexual 

 organs have been thoroughly studied, with the exception of 

 certain lichens and the Laboulbeniaceae in which the conditions 

 are very different and will be considered later. 



The problem then will be: Did the uninucleate condition of 

 the gametangium, as represented by Sphaerotheca, come from a 

 multinucleate gametangium (coenogamete) illustrated by Pyro- 

 nema, or is it the progenitor of the latter? We have no series 

 of forms in the Ascomycetes such as the four species of Albugo 

 studied by Stevens to help us to a conclusion. But the problem 

 in the Ascomycetes seems to be identical with that of the 



