NUCLEAR BEHAVIOR IN PROMYCELIA 
45 
more than two cells fuse and this leads to the production of aecidio- 
spores that contain more than two nuclei. The behavior of the nuclei 
in these spores during germination is a problem which I have not yet 
been able to solve. The age of the mycelium which bears the aecidio- 
spores is not known. It is generally supposed to be approximately 
one year old but this question cannot be settled without experimental 
evidence. It is interesting to note in this connection that Miiller 
found that the mycelium which produces most of the aecidiospores of 
Endophyllunt Euphorbiae silvaticae is two years old. The binucleate 
aecidiospores become uninucleate, presumptively by nuclear fusions 
during the early stages of germination. Two successive divisions of 
the nucleus of the aecidiospore produce the four nuclei of the pro- 
mycelium and each nucleated cell of this promycelium produces a 
sporidium. 
I am inclined to believe that Caeoma nitens is a rather primitive 
form among the rusts. The predominance of the gametophytic gen- 
eration over the sporophytic generation is strong evidence in favor of 
this view. This is the condition which we generally meet with in the 
lower forms of plant life. Those rusts in which the sporophytic 
generation has become the important stage are probably higher in the 
scale of evolution than such forms as Caeoma nitens and Endophyllum 
sempervivi. Caeoma nitens should also be regarded as more primitive 
than Endophyllum, since it possesses a simpler form of aecidium. 
I am greatly indebted to Dr. R. A. Harper and Dr. W. G. Mar- 
quette for advice and criticism while engaged in this work. 
Columbia University, 
New York City 
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