82 
GEORGE F. ATKINSON 
atmosphere under the bell jars. No attempt was made to keep the 
aecidiospores from falling on them. In fact some of their leaves 
were well dusted with aecidiospores, but on none of them did teleuto- 
sori appear. For several years I have examined the dewberry plants, 
in the patch where the Caeoma is so abundant, for teleutosori and 
have never been able to find any. If the normal history of the Caeoma 
on these dewberry plants was a two-generation cycle, one would expect 
to find, on the leaves of the shoots which have outdistanced the 
perennial mycelium, some teleutosori. 
The production of teleutosori on those plants surrounded by a 
chilled moist atmosphere during the period when the aecidiospores 
were germinating indicates that, because of the lowered temperature, 
the aecidiospores, or at least many of them, did not germinate by a 
promycelium, but by an ordinary germ tube, which entered the host 
leaf forming a diploid mycelium from which the teleutospores arose. 
Germination of the aecidiospores of Caeoma nitens, therefore, appears 
to be selective, the mode of germination being determined by tempera- 
ture conditions. When the temperature is comparatively high, they 
assume the function of teleutospores. 
Gymnoconia peckiana, therefore, is an interesting example of a 
species in which the life cycle is not permanently fixed. In its more 
southern distribution, where the temperature, at the time of germina- 
tion of the aecidiospores, is comparatively high, it is generally (perhaps 
always) a one-generation cycle species. In its more northern distri- 
bution it is often, perhaps usually, a two-generation cycle species. 
In the intermediate region it has sometimes a one-generation cycle, 
at other times a two-generation cycle, probably depending on the 
local and seasonal temperatures at the time of germination of the 
aecidiospores. The general areas of distribution are, in general, well 
shown by Arthur, though germinations of the aecidiospores have not 
been tested over the entire area. Central New York lies in the inter- 
mediate climatic zone of the distribution of the species. On the 
ground of the determinating influence of temperature in the selection 
of a one-generation or two-generation cycle we would expect the 
existence here in the vicinity of Ithaca, N. Y., of both cycles. Ob- 
servation over a period of years has shown that in certain years 
Puccinia peckiana is not uncommon, while in other years it apparently 
is very rare. No attempt has been made here to correlate the abun- 
dance or scarcity of the Puccinia peckiana in different years with the 
temperature conditions. But it would seem reasonable to expect 
