158 Transactions British Mycological Society. 
at 2-3° C., not more than 5 % at 22~-23° C. and no germination 
at all at 29-30° C. 
On the strength of some further trials the writer has come to 
the. conclusion that the uredospores of P. glumarum germinate 
better than either of the other two rusts at 2-3° C. At 22-23° C. 
(near the upper limit) those of P. graminis germinate better 
than P. tviticina but those of P. glumarum show very poor 
germination. 
Above 5° C. and up to 20° C. all the three rusts germinate well. 
It has been pointed out above that black rust cannot withstand 
cold, whereas both yellow and brown rusts resist it well. This 
fact is further borne out by the results of a large number of 
experiments conducted at different times of the year with 
uredospores of almost the same age after exposing them to low 
temperatures in cold storage. The material used in these experi- 
ments was cultivated in the laboratory. In all the experiments 
the controls were kept at laboratory temperatures at which the 
germination tests were made. The following is a brief summary 
of the results: 
A. Black rust (P. graminis). 
After exposure to — 6-5 to — 10° C. for 24 hours the uredo- 
spores of this rust do not show even 10 % germination and 
after four to seven days there is a total loss (only one or two 
spores germinating) of viability. 
When exposed to 2:5°C. the spores retain nearly 10% 
viability even after one month. They show as much as 50% 
germination after exposure to 5° C. for a month. 
B. Brown rust (P. triticina). 
The uredospores of this rust on the other hand show as much 
as 50-60 % germination after exposure to — 6:5 to — 10°C. 
for twenty-four hours and even after a week retain nearly 30 % 
of their viability. After one month’s exposure their viability 
falls to 15 %. 
At 2:5° C. and 5° C. the uredospores retain as much as 25 % 
of their viability after a month’s exposure. 
C. Yellow rust (P. glumarum). 
After exposure to — 65 to — 10° C. for twenty-four hours the 
uredospores of this rust germinate quite as well as those of 
brown rust. After four days they show nearly 25 °%% germination, 
but by the end of a week only 10 % spores are viable. At 
25°C. and 5° C. they retain 15-20 % of their viability after an 
exposure for one month. 
It is essential to point out that the above results are not 
absolutely constant and that casual variations in the per- 
