1198 Wisconsin Academy of Sciences, Arts, and Letters. 
fusions similar to those in Phrag. speciosum in the formation of 
the primary uredospores of Phragmidium potentillae-canadensis 
and further (9) published a general account of the spore forms 
in the rusts in which he advances the view that the aecidio-, 
uredo-, and teleutospores are only a series of asexual repio- 
ductive stages arising from morphologically equivalent basal 
cells in the sporophyte generation and that one form of spore 
may replace the other; if there are no aecidiospores, the sporo¬ 
phyte generation begins with the uredospores, etc. 
It will he seen from the above that while our knowledge of 
the number of nuclei in the mycelium and the origin of the bi¬ 
nucleated condition of the cells of the rusts does not as yet, 
cover nearly all the species, still we are sure of enough to make 
some generalizations. It has now been fairly definitely estab¬ 
lished that all forms of spores in the rusts are binucleated begin¬ 
ning with the aecidiospores, or if they are suppressed, with the 
uredospores, and that the mycelium that is produced from these 
spores has binucleated cells up until the formation of the teleu¬ 
tospores when the nuclei fuse. There is further, considerable 
evidence that the reduction divisions occur in the formation of 
the four cells of the promycelium and that from these come un- 
inucleated sporidia which in their turn develop into a my¬ 
celium with uninucleated cells. 
Por an understanding of the life cycle of the smuts it will al¬ 
so be necessary to review the cytological work that has been done 
on the nuclear phenomena and on the spore formation of the 
Basidiomycetes. This group while not so nearly related to the 
ITstilagineae still has much in common with them in the homol¬ 
ogous structure of basidium and promycelium and of basidio- 
spores and conidia. 
It was established during the ? 90’s by the work of Bosen y 
Wager, and Dangeard that the cells of the carpophore are fre¬ 
quently multinucleated while the basidia are at first binucleated 
hut later become uninucleated by the fusion of the two nuclei. 
Maire (29) in 1902 found that in a number of species the 
cells of the sub-hymenial layer are binucleated while many of 
those of the stipe and pileus were multinucleated. He did not, 
