162 . Transactions British Mycological Society. 
Pot No. 3. In the open throughout—spores 60-70 % ger- 
mination. 
Pustules on the 34th day. 
On the strength of these results one can easily explain why 
in a colder part of the year the rust took nearly ten to eleven 
weeks from the probable time of its having gained entry into 
the young seedlings, to develop pustules. The lowest tem- 
perature in the shade for February 1921 was 23° F., the highest 
was 61° F., the average minimum was 33°3° F. and average 
maximum 47°6° F. 
Hecke* in Austria has shown clearly that the upper limit of 
the incubation period in the case of yellow rust may go up to 
five months in a winter which was much more severe than the 
one we had, except for one week in the middle of December in 
the year 1920-21. He inoculated wheat on October 28th, which, 
exposed to winter cold, did not develop pustules till March 
28th. 
Undoubtedly a very severe winter with more frequent frosts 
may prolong this period by a few weeks, and if the earlier part 
of spring also happens to be cold, pustules may not appear 
till summer actually begins. 
It would be useless to enter into the details of all the experi- 
ments conducted on the length of the incubation period of this 
rust under different conditions so only the results of a few 
conducted in the open will therefore be given. 
1. Wheat inoculated Feb. 23rd, 1921 Pustules on the 25th day. 
2. ke - March 24th, 1921 LY 5.) MARE as 
3. e if Oct. 26th, 1921 vs Pe 6 hao 
2 ag a De . March 3rd, 1922 - i.) 26thes 
It is probable that during winter the rust mycelium inside 
the host grows by fits and starts rather than remains altogether 
latent, because even in the middle of winter the weather may 
occasionally be favourable for its growth and fresh pustules 
may be formed. 
That the recurrence of brown rust has a similar explanation 
will be clear from the following summary of experiments con- 
ducted during the spring, autumn and winter of rg2r. 
1. March 28th: 
(a) Wheat inoculated in the open and _ Pustules on the 
kept in the open 15th day. 
(6) Wheat inoculated in tropical pit at — Pustules on the 
the Botanic Garden 8th day. 
* Hecke L., Naturw. Zeitschr. f. Forst- u. Landwirtsch. 1x, p. 44 (1911). 
