June 7,1924 
Uninucleated Aecidiospores in Caeoma Nitens 
1049 
spermogonia. A few 2-celled promycelia were seen in cultures from this collec¬ 
tion. A blackberry from Doctor White's plot at the Arlington Experiment 
Farm in Virginia regularly shows rust with spermogonia, yet practically every 
spore produces a 2-celled promycelium. Sections show that the spores are 
mostly uninucleated. One other specimen sent in appears to be of the same 
nature. So far as has been learned, every specimen of this interesting form 
occurred on a cultivated variety of blackberry. It is the only form with sper- 
mogonia so far studied that has uninucleated aecidiospores. 
CHARACTERISTIC FEATURES OF PROMYCELIA OF THE SHORT- 
CYCLED ORANGE-RUST 
In the preceding discussion, in order to avoid confusion, no mention has been 
•made of the great variability which may sometimes occur in the form and size 
of the promycelia which develop when spores from a single aecidium are germ¬ 
inated. Likewise, the promycelia were said to be 2-celled or 4-celled, as the 
case might be, disregarding the fact that in certain germination tests promycelia 
with from 3 to 8 cells were found. Furthermore, the number of cells which a 
promycelium develops does not necessarily correspond to the number of nuclei 
visible or to the number of sporidia that finally mature. Various types of promy- 
oelia, as they appeared in the germination test cultures, will be described. The 
method of origin of the chains of aecidiospores and the behavior of the nuclei 
during germination and formation of sporidia will then be considered. 
As a rule, the aecidiospores of the strain which seems to omit the spermogonial 
stage are smaller than those of the long-cycled form. The color characters of the 
^ecidia are not always dependable, but, in general, when the aecidia are rather 
light yellowish-orange as contrasted with reddish-orange colored (PI. 1, B, D) the 
spores will be found smaller, and less uniform in shape and size. These small spores 
s,re the ones that regularly produce 2-celled promycelia on germination. The more 
common types of this promycelium are shown in Plate fi, A to I. 3 Two septa 
are usually plainly visible, cutting off two cells, leaving the spore and a short 
piece of the germ-tube without cytoplasmic contents. The promycelia are 
rather slender and their sporidia are not large. As compared with these struc¬ 
tures developing from the large spores matured by other short-cycled strains, 
they are certainly smaller. In cultures of germinating spores from plant No. 
497 no promycelia were found with four sporidia attached. Plate 5, H, shows 
three sporidia on a 2-celled promycelium which is rather “abnormal". Some¬ 
times by following this type of growth a little further, one will find that the 
•contents of one of the sporidia will disappear so that only two finally are dis¬ 
charged. The sterigmata are frequently long and filamentous (PI. 5, D). This 
seems to be due to the conditions under which the spores germinate. Normal 
sporidia are finally developed. 
The more common types (4-celled) of promycelia developed from spores of 
strains producing spermogonia are shown in Plate 5, J to M. These are 4-celled 
and will all develop four sporidia. 
Certain odd types are also figured. They are, however, perfectly normal. 
A 9-celled promycelium is shown in Plate 5, N. Some of the cells are dead or 
•empty but six sporidia are being matured. Forked promycelia are not very 
Tare. Figure R shows one with eight cells, six of them alive; one sporidium has 
been discharged, two more are matured, and one is just forming. 
The influence that the conditions attendant on spore germination have on 
the form of the promycelia is occasionally very astonishing. For example, the 
spores from plant No. 569 develop in the warm laboratory very long germ 
1 The 4-mm. dry lens was used in drawing the figures in Plate 5; the 1.5-mm. oil immersion lens for Plates 
H to 4, inclusive. 
