164 Transactions British M ycological Soctety. 
(6) Wheat inoculated in the laboratory removed to the 
open after four days. Pustules 27th day. 
(c) Wheat inoculated in the laboratory and removed to 
unheated greenhouse. Pustules 22nd day. 
(d) Control in the laboratory throughout. Pustules roth 
day. 
eles minimum temperature in shade during February 
1922 was 33°5° F. 
Average maximum temperature in shade during February 
1922 was 48° F. 
From the last two experiments it is clear that the mycelium 
of black rust can survive milder weather and but for the absence 
of the source of infection might appear on the cereal crops in 
the earlier part of spring, if weather conditions were favourable. 
But the source of infection (uredospores) cannot survive the 
more severe part of winter, and it is highly probable that the 
mycelium also cannot do so. 
As there was no black rust available in the open, the material 
used for the above experiments was such as had been cultivated 
in the laboratory. In every case after inoculation the pots were 
kept indoors for two to four days before removal to the open, 
to give the fungus a good start. Still it was only in the experi- 
ments conducted in more favourable weather that any positive 
results were obtained. 
That the incubation period may be prolonged even under 
higher temperatures is clear from what happened in one of the 
experiments last summer (1921). 
Out of the six seedlings of Burbanks wheat inoculated with 
yellow rust in the laboratory on July 26th, and kept indoors 
under protection from direct sun, only one developed pustules, 
and that on the seventeenth day; other inoculated spots were 
dead and shrivelled by then. 
Again Red Sudan wheat inoculated on August 8th with 
yellow rust and removed to the open after two days showed 
pustules on the eighteenth day but the infection was very poor. 
Av. minimum temp. in July 53°8° F.. Max. 79°4° F. 
= 7 Aug. 52°7° F. Max. 70°9° F. 
It may be remarked, that wheat inoculated on the 6th of 
June with yellow rust developed pustules on the ninth day. 
The writer has great pleasure in being allowed to quote from 
the unpublished work of Dr Burns some interesting data which 
have a direct bearing on this question. 
Dr Burns inoculated very susceptible varieties of wheat with 
black rust on the 16th of May 1909 at Poona in India, under 
the shade of a mango tree to protect seedlings from the hot sun 
and the plants developed pustules on the thirty-fifth day. 
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