DODGE: STUDIES IN THE GENUS GYMNOSPORANGIUM 137 
two lying further back, the other two occupying separate branches. 
A cell wall is finally laid down, cutting off the outer portion of the 
germ tube containing the nuclei and most of the cytoplasm (Figs. 
8-10). This curious method of germination is in no sense similar 
to the development of a promycelium, though four nuclei are pro- 
duced in each case. It may be that it is fairly common among the 
rusts as Sappin-Trouffy has pointed out.’ Whether or not it is pos- 
sible to find an appropriate artificial medium for the development of 
the mycelium of a rust in artificial cultures, it would seem that such 
cases as these afford at least a starting point. Four-nucleated germ 
tubes are the rule in these cultures, but fully developed tubes with 
only two nuclei are not difficult to find (Fig. 11). 
In some of my cultures in which the petiole of a leaf had been 
infected at the junction with the blade, it was found that the winter 
bud was larger than usual. The mycelium must have run down the 
petiole and become established in the bud. When such plants were 
put in the cold frame over winter and taken out in the spring, these 
buds developed small leaves which at once became evenly covered 
with spermogonia and later were transformed into large galls from 
which aecidia developed quite normally. 
In some cases the mycelium seems to penetrate into the tissues of 
the stem where a spindle-shaped swelling or burl is formed. In the 
following spring a green gall bursts out through the cork, forming a 
nodular swelling outside and from this spermogonia and aecidia are 
produced. I have had several cases in which Roestelia transformans 
has survived the winter and developed aecidia the following spring 
The same is true in my cultures of R. Botryapites. In October, 1915, 
winter buds of six Amelanchiers showed signs of being infected. All 
of these survived the winter and developed spermogonia and ripened 
aecidiospores in the month of June, which is several months earlier 
than they can be found in nature. These are not cases where the 
formation of an aecidium has simply been delayed. On the con- 
trary, an entirely new crop of spermogonia arises from newly formed 
tissue, new gall growth, and we find the aecidia developing as in 
normal cases of infection with sporidia. 
(GYMNOSPORANGIUM FRATERNUM 
The buffer cells in the teleutospore sori of G. fraternum are much 
more striking in appearance, forming as they do a perfectly even 
palisade layer that frequently extends entirely across the sorus without 
interruption (Text-fig. 4). This is a very characteristic feature of 
8 Sappin-Trouffy, P. Recherches histologiques sur la famille les Urédinées. 
Le Botaniste 5: 59-244. f. I-69. 1 D 1896. 
