No. 460.] STUDIES 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 (:01), 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 
