NUCLEAR BEHAVIOR IN THE PROMYCELIA OF CAEOMA 
NITENS BURRILL AND PUCCINIA PECKIANA HOWE^ 
Louis Otto Kunkel 
In a preliminary paper (lo), I have shown that the aecidiospores 
of Caeoma nitens Burrill produce promyedia. The behavior of the 
nuclei during the germination of these spores was not described at 
that time and has been the subject of my further studies. 
Tulasne (19) in 1854 found that the aecidiospores of Endophyllum 
Euphorbiae silvaticae do not germinate as normal aecidiospores. 
Instead of forming non-septate germ tubes, these spores produce 
promycelia. Morphologically considered they are aecidiospores ; never- 
theless, they function as teleutospores. Sappin-Trouffy (17) also 
studied them and confirmed the observations of Tulasne as to the 
manner of their germination. According to Sappin-Trouffy, however, 
the behavior of the nuclei in the germination of this aecidiospore 
differs from that in a normal teleutospore. The two nuclei in this 
case do not fuse but pass directly out into the tube of the promycelium 
where they divide to produce the four nuclei. 
Maire (12) also made a cytological study of the aecidiospores of 
E, Euphorbiae silvaticae. He agrees with Sappin-Trouffy that nuclear 
fusions do not occur in them. He also studied the aecidiospores of 
E. sempervivi and decided that here again the nuclei do not fuse but 
pass out into the germ tube and divide, just as in the case of E. Eu- 
phorbiae silvaticae. 
More recently Hoffmann (8) has made a very careful cytological 
study of E. sempervivi. He finds that a nuclear fusion does occur 
in the aecidiospores of this rust and that the four nuclei of the pro- 
mycelium arise by two successive divisions of the fusion nucleus, just 
as in the case of ordinary teleutospores. He showed that the first 
or even both of these divisions may take place in the aecidiospore. 
This observation suggests that the two nuclei, which according to Maire 
(12) pass out of the spore into the promycelial tube are the product 
^ Contributions from the Department of Botany, Columbia University. No. 
259. 
37 
