No. 460.] STUblES ON PLANT CELL.— V. 245 



for sexual processes at other periods more closely associated 

 with the development of teleutospores or basidia. 



The conjugation of yeast cells has many points of similarity 

 to the fusion of conidia in the Ustilaginales. This phenomenon 

 has been discovered in an organism obtained from commercial 

 ginger by Barker (:oi), which he calls Zygosaccharomyces, and 

 in three species of Schizosaccharomyces by Guilliermond (:03). 

 The conjugation in all forms immediately precedes spore forma- 

 tion and involves a nuclear fusion as well as, that of the cyto- 

 plasm. The conjugation is followed by division of the fusion 

 nucleus and spore formation in the united cells. The con- 

 jugating cells are sisters in the species of Schizosaccharomyces 

 but apparently may not be closely related in Barker's form, 

 Zygosaccharomyces. Both investigators regard the conjugation 

 as a sexual act, and Guilliermond considers the fusion cell to be 

 an ascus with the value of a zygospore. These conclusions do 

 not seem to the writer convincing. Spore formation in the 

 yeasts has not been shown to present any of the peculiarities of 

 nuclear division and free cell formation as described by Harper 

 for the ascus, and until such are established it is hardly safe to 

 conclude that the yeasts are Ascomycetes. Whether or not the 

 conjugation is a sexual process becomes a question of phylogeny 

 and we know too little of the history and relationships of the 

 yeasts to assert that the conjugating cells are morphologically 

 gametes. Again, the view that yeasts are derived from conidia 

 or mycelia of higher fungi which have continued a simple 

 growth by budding in peculiar and favorable media is rather 

 against any view that we are dealing here with a simple or 

 primitive sexual act. There are very striking resemblances to 

 the fusions of conidia in the Ustilaginales, which were described 

 in the previous paragraph and do not appear to be sexual proc- 

 esses. It is unsafe to assume sexuality because the conjuga- 

 tion precedes spore formation, because in most yeasts spore 

 formation takes place regularly without conjugation. Is it not 

 rather another illustration of cell and nuclear fusions related to 

 nutritive processes alone .? 



Some of the most interesting nuclear fusions, apparently 

 associated with the apogamous development of a sporophyte are 



