INTRODUCTION 3 



strated that in Achlya debaryana fertilisation does occur, 

 id probably also in other allied species. 



Trow's discovery, however, does not prove that the con- 

 clusions arrived at by others are incorrect ; as previously 

 stated, in species closely allied, some may still retain 

 a sexual mode of reproduction, others not. 



In the Ascomycetes Harper has demonstrated the 

 :currence of a sexual process in Sphaerotheca Castagnei, 

 Pyronema confliicns^ etc. 



Finally, Blackman has recently announced the discovery 

 of a sexual mode of reproduction in the Uredineae. This 

 consists in the fusion of two nuclei in certain cells in the 

 Aecidium stage. This, however, does not conform with the 

 definition of sexual reproduction as stated above, and as it 

 occurs at a definite stage in the individual immediately 

 preceding the formation of spores, it may possibly prove 

 to be homologous with the fusion of nuclei noted by 

 Dangeard in the Ascomycetes and the Basidiomycetes. 



The last-named author has shown that in the Basidio- 

 mycetes, a fusion of two nuclei takes place in the basidium, 

 which is considered as an oospore. In the Ascomycetes 

 a similar fusion of two nuclei occurs at the base of the 

 young ascus. Both instances are considered by Dangeard 

 as examples of true sexual reproduction, who consequently 

 does not admit Harper's statement respecting Sphatrotheca. 

 This fusion of nuclei in all cases just precedes the forma- 

 tion of spores. 



This view is not generally accepted, one reason being 

 that it occurs in certain species where undoubted sexuality, 

 as defined above, exists, as in Sphaerotheca^ etc. On the 

 other hand, this fusion of nuclei in the higher groups of 

 fungi appears to fulfil physiologically the functions of true 



