20 6 RESEARCHES ON FUNGI 



Another possible explanation of the absence of conjugate nuclei 

 and of the non-occurrence of karyogamy in Sporobolomyces is that 

 in this genus all traces of a sexual process have disappeared. As 

 Kluyver and van Niel * have pointed out, in this connexion facts 

 concerning the Saccharomycetes may be cited for comparison. 

 Guilliermond 2 has shown that in this group of Yeasts, in which as 

 defined by him all the species form ascospores, there is a gradual 

 transition between species in which conjugation takes place between 

 two neighbouring cells with resultant karyogamy (Schizosaccharo- 

 myces, Zygosaccharomyces, Debaryomyces) to species in which all 

 traces of conjugation and of karyogamy have completely disappeared 

 (Saccharomyces). If such yeasts as Saccharomyces cerevisiae have 

 ceased to show any signs of sex and yet are able to form ascospores 

 non-sexually, there may be Basidiomycetes which have lost all 

 trace of sex and yet are able to form basidiospores non-sexually ; 

 and, further, the species of Sporobolomyces, which resemble the 

 species of Saccharomyces in their vegetative budding, may be just 

 such Basidiomycetes. 



For the reasons set forth in the above discussion I have come to 

 the following conclusions : 



(1) From the point of view of phylogeny, the most important 

 characteristics of Sporobolomyces are : (a) the peculiar shape of the 

 conidium which is due to its possessing an excretory hilum that is 

 developed on one side of the top of the sterigma^ (6) the presence of 

 a sterigma of typical conical shape beneath each conidium, and (g) 

 the discharge of the conidium by the drop -excretion mechanism. 



(2) The possession of the characteristics just enumerated, which 

 are identical with those concerned with the production and liberation 

 of individual basidiospores in all Hymenomycetes and Uredineae, 

 clearly indicates that Sporobolomyces belongs to the Basidiomycetes. 



(3) The behaviour of the nuclei in Sporobolomyces, as ascer- 

 tained up to the present, cannot be used as an argument either for 

 supporting or for rejecting the conclusion that Sporobolomyces 

 belongs to the Basidiomycetes. 



1 A. J. Kluyver and C. B. van Niel, loc. cit., pp. 393-394. 



2 A. Guilliermond, The Yeasts (translation by F. W. Tanner, New York), 1920, 

 pp. 48^9, 193-232. 



