June 7,1924 
Uninucleated Aecidiospores in Caeoma nitens 
1057 
event, spermogonia would be formed, but cell fusions being omitted the aecidio¬ 
spores would be uninucleated. If the sporidium from the opposite end produced 
infection it could only be by a gynogenetic process. In such an event, no sper¬ 
mogonia would appear, no cell fusions would occur, and 1-nucleated spores 
would arise. 
The two strains evolved should remain or continue to be true to form, but by 
bringing about a double infection with a sporidium of each sort one would obtain 
a strain with spermogonia, cell fusions, 2-nucleated aecidiospores and 4-celled 
promycelia. The difficulty with which one is able to infect a blackberry systemi- 
cally and the rareness with which natural systemic infections occur in comparison 
with the vast number of spores shed, would suggest that this hypothesis should 
not be entirely ignored. One is reminded that future infection work with the 
orange-rusts should be carried on with spores at least from a single plant and 
ultimately with single aecidiospores and even with single sporidia. 
SUMMARY 
Certain strains of the short-cycled orange-rust on Rubus do not develop sper¬ 
mogonia except perhaps as they are aborted or vestigial. 
The aecidiospores in such strains are for the most part uninucleated. Binu- 
cleated or multinucleated spores are sometimes present in such aecidia. 
Cell fusions do not occur at the origin of a chain of uninucleated aecidiospores. 
The number of nuclei in an aecidiospore may be increased by nuclear divisions. 
The size of an aecidiospore'varies with the number of nuclei present at its 
maturity. The uninucleated spores are much smaller than those with two or 
more nuclei. 
A spore with one nucleus germinates normally; its nucleus divides once so that a 
2-celled promycelium Which matures two sporidia is formed. 
The number of cells in a promycelium and the number of sporidia matured is 
not fixed, but depends to a great extent on the number of nuclei in the aecidiospore. 
A poly nucleated spore is very large and would probably give rise to a promycelium 
with more than four cells and very likely some of the cells would contain more 
than a single nucleus. 
Degeneration of nuclei sometimes occurs in the cells of promycelia and certain 
of its cells may die, so that the number of sporidia eventually formed does not 
necessarily correspond to the number of nuclei originally present. 
So far as yet observed spermogonia are always matured by the long-cycled 
rust Gymnoconia interstitialis and cell fusions occur. 
Strains of the rust which commonly form 4-celled promycelia when the aecidio¬ 
spores are germinated always develop spermogonia. In this fofm the bihucleated 
aecidiospores arise as the result of cell fusions. 
That nuclear fusions always occur in the aecidiospore or its promycelium in 
the short-cycled orange-rust is questioned. 
So-called “abnormal” promycelia with other than the traditional number, 
four, cells are accounted for by nuclear behavior during spore development and 
germination. When a spore has but one nucleus, that nucleus divides only 
once during the formation of the 2-celled promycelium. 
Binucleated spores arising from cell fusions usually develop 4-celled promy-r 
celia, possibly without nuclear fusions followed by reduction divisions. On this 
principle a precocious division of the nuclei in a spore followed by a multicellular 
promycelium need not introduce a new element into the inheritance of the rust. 
