1050 
Journal of Agricultural Research 
Voi. xxviii, No. m 
tubes (PI. 5, V), resembling those of the long-cycled Gymnoconia. They be^ 
come 4-celled, however, and mature four sporidia. Plate 5, S, shows such a 
promycelium as it would appear a little later. Five-celled promycelia (PI. 5*. 
T) with one sporidium from each, are sometimes seen in cultures. The forma¬ 
tion of five cells and five nuclei after a reduction division is not the regular order 
of procedure as commonly understood. These odd types of germination are 
referred to in order to focus attention on the question of nuclear behavior during: 
and after aecidiospore formation, and to raise the question as to whether or not 
nuclear fusions followed by reduction divisions are always to be found in the 
short-cycled orange-rusts. 
While every specimen of the rust so far discovered which omits its spermo- 
gonial stage is characterized by 2-celled promycelia, as previously noted, there 
are certainly clear-cut cases where spores from leaves with spermogonia are 
uninucleated and develop 2-celled promycelia with only two sporidia (PI. 5, 
ORIGIN OF AECIDIA WITH BINUCLEATED AECIDIOSPORES 
In the light of what is known of the vagaries of Rubus orange-rusts, it is im¬ 
possible to say what was the nature of the material which Olive (13) used as the 
basis for his cytological work on the orange-rust. It was gathered in Indiana 
on Rubus sp. He figures the Christman cell fusions referred to as “sexual fusions.” 
The rust that Olive studied evidently conformed in every way to what might be 
expected of the long-cycled form Gymnoconia. 
Kunkel (5) presumably did not find anything in his studies of the develop¬ 
ment of the aecidial sorus of the short-cycled form of the orange-rust to suggest 
that there might be at times some departure from the regular order of procedure 
in the growth of the aecidium. According to him the two nuclei originally 
found in the aecidiospore fuse before germination of the spore and as the germ 
tube begins to push out the fusion nucleus divides, sometimes while yet in the 
spore; the first division may also occur in the promycelium. After the second 
division the cross walls are laid down so that four uninucleated cells comprise 
the mature promycelium. Each of the four cells then develops a sporidium 
containing a single nucleus. In the manner of their origin, in the behavior of 
their nuclei on germination, and in the type of promycelia formed from them, 
the aecidiospores of Caeoma nitens were thus, according to Kunkel, not un¬ 
like those of Endophyllum sempervivi as reported by Hoffman (4) and others. 
The writer’s studies have been confined to preparations made from material 
obtained from plants infected with rust whose spores have been germinated. 
There are many interesting features in the development of aecidia which need 
further attention other than the so-called “sexual fusions,” but as the question 
relating to the ultimate form of the promycelium is in the main determined at 
the origin of the aecidiospore, it will be necessary to give this phase of the subject 
some attention. Disregarding what occurs when the aecidia of the long-cycled 
orange-rust are formed (PI. 2, T), the origin of the chains of spores in those 
strains where 4-celled promycelia are regularly developed from aecidiospores 
will first be referred to. Cell fusions (PI. 2, M to S) in numbers can be 
found in sections of aecidial primordia of the rust on an Iceberg blackberry 
No. 543. Spermogonia were developed in large numbers on this plant and 
germination tests showed that most of the spores germinated as short-cycled, 
forming quite regularly 4-celled promycelia. Binucleated spores and inter¬ 
calary cells are cut off in regular order above the fusion cells. 
In no case is there any indication in these sections of a fusion of the two nucle i 
in a spore. Hoffman (4) shows that in Endophyllum sempervivi the two nuclei 
