June 7 ,1924 Uninucleated Aecidiospores in Caeoma Nitens 1051 
fuse and then often undergo the first division before the spore is shed. The 
writer's sections of telia of the long-cycled form Gymnoconia show that the two 
nuclei fuse as the teleutospore reaches maturity. Is it possible that the two 
nuclei of the short-cycled orange-rust spore never fuse? If so, the reduction 
division would be omitted, only that standing in place of the homoeotypic division 
persisting to give the four nuclei of the “normal” promycelium. 
In some preparations from an infected loganberry “two-legged” cells are very 
difficult to find (PI. 2, L). Very likely such figures represent sections at right 
angles to the pairing cells so that only one of the “leg” cells appears in the 
section. It is not impossible that chains of binucleated spores may sometimes, 
or even regularly, arise by mere nuclear division as claimed by Kursanov (8). 
It is certainly strange that fusion cells are so hard to find in this strain on logan¬ 
berry. 
Rust from a blackberry also shows aecidial chains of 2-nucleated spores 
(PI. 2, I, J) where it is also difficult to understand why more examples of two- 
legged fusion cells are not to be found. The cytology of this form of the orange- 
rust is being given further attention. 
ORIGIN OF SORI WITH CHAINS OF UNINUCLEATED AECIDIO¬ 
SPORES 
There being no question as to the existence of cell fusions, at least in the 
aecidium primordium of the Gymnoconia orange-rust, the form of rust on black¬ 
berry which omits the spermogonial stage will next be considered. 
Plate 2, A, represents merely in outline and position the structures in an 
aecidial sorus of the rust on Crandall blackberry which was obtained May 17, 
1922. The uninucleated basal cells arise from uninucleated cells of the sorus 
primordium. Intercalary cells are cut off and the spores are matured in a normal 
fashion. There were no cell fusions in this sorus. At B a chain of 2-nucleated 
spores and interstitial cells is shown adjacent to chains of uninucleated spores. 
Kursanov ( 6 ) says, in effect, that in Aecidium leucospermum this would mean 
that the nucleus of the original basal cell simply divided and thereafter 2-nucleated 
cells are cut off. In Plate 2, D and F, are shown chains of spores in an aecidium 
from plant No. 497, most of whose spores produce 2-celled promycelia. At F the 
two lower cells in the chain are clearly uninucleated while the spores above are 
binucleated, but at E the basal cell is binucleated. In some forms scarcely a 
binucleated spore can be found in a sorus. At G is shown a very young sorus, 
and at H, a somewhat older one where from first to last the cells are uninucleated. 
As noted, cell fusions regularly occur in the aecidium of the long-cycled orange- 
rust (PI. 2, T). By triple or quadruple fusions, 3 and 4 nucleated spores presum¬ 
ably may arise as in the other rusts. What would this mean in germination and 
in infection ? In forms of the short-cycled Caeoma rust with spermogonia where 
cell fusion would be expected to occur frequently, binucleated spores may possibly 
arise without such fusions. Then, too, 3-nucleated spores are not at all rare in 
iihese forms (PI. 2, K). In strains without spermogonia and with uninucleated 
spores originating without fusion there are also 2-nucleated spores, possibly 
formed as the result of nuclear division and also from cell fusions. By studying 
stained preparations of germinating spores the writer becomes more thoroughly 
convinced that the orange-rusts represent forms which are not fixed in their life 
cycles. Bearing in mind the facts regarding the methods of origin of the aecidio¬ 
spores one may understand more readily why there is such a great variation in 
the forms of promycelia. 
96461—24f-7 
