76 Wisconsin Academy of Sciences, Arts, and Letters. 
to the point where they originate by the division of a single nu¬ 
cleus in the germination of the sporidium accordng to the au¬ 
thors cited. The two nuclei which fuse maintain a separate 
existence throughout almost the entire life cycle of the rust. 
There can be no question as to the long continued separate ex¬ 
istence of the fusing nuclei nor as to the fusion itself. This 
fusion results in Coleosporium in a, renewed tendency to growth 
on the part of the cell containing the fusion nucleus. 
In Closterium Klebahn (10) found that in the zygote the 
pronuclei remained separate for some time. In Cosmarium he 
found a similar condition. Hacker (13) has shown that in 
Cyclops the two sexual nuclei maintain a relatively independ¬ 
ent existence at least through the early stages of the cleavage 
of the egg. There is some evidence that the chromosomes in 
the division of the fusion nucleus of the rust are collected into 
groups on the spindle (Tigs. 18, 19 and 20). It is quite pos¬ 
sible that these two groups of chromosomes, are respectively the 
chromosomes of male and female nuclei not yet combined. 
Raeiborski (5), in view of the fact that a longer or shorter 
period of development, exists between the fusion of the cyto¬ 
plasm and the fusion of the nuclei in the. cases mentioned above 
and also even more notably in the case of Basidiobolus, holds 
that the entire life cycle of the rust from, the germination of 
the sporidium to the fusion of the nuclei in the teleutospore 
is to be interpreted as an intercalation between cell fusion and 
nuclear fusion in a single sexual act. The division of the 
nuclei without cell division in, the young mycelium represents 
for him a cell fusion, the nuclear fusion occurring long after 
in the teleutospore. The evidence cannot be regarded as suf¬ 
ficient to establish this view. It is not yet established for a 
sufficient, number of forms at what stage the binucleated cells 
with conjugate nuclei first appear in the life cycle. 
There is as yet no evidence of any proper cell fusion in the 
rusts though the fusion of the nuclei in the teleutospore has the 
essential characteristics of a sexual fertilization in the origin 
of the nuclei and in the behavior of the teleutospore after 
fusion as described above. The existence of nuclei in the 
mycelial cells, maintaining independent, lines of descent, for in¬ 
definite periods, has perhaps made cell fusion unnecessary. 
