.294 Ward . — On Relations between Host and Parasite 
germinating at 20-22° C, so we may assume that no source of 
error existed there. 
The infection was done by sopping up spores in paper pulp, 
as I found them stick so" much better. Each infected plant 
was then put in the west window under a beaker kept wet 
with filter-paper — my usual method. 
July 6 — the day of infection of No. 747-— opened dull and 
cool, the shade temperature being 16-19*5° C and it rained 
hard in the later part of the day. 
July 7 was warm, close and dull, with sunny intervals later. 
Shade temperature 22° C at 10 a.m. 
July 8 was bright, hot with cool easterly breezes. 
July 9, overcast and dull muggy morning, t. = 19*5° C at 
11 a.m. Hot and sunny bursts later. 
July 10, 11, 12 and onwards were scorching hot days. 
It seems impossible to find any source of error in the 
temperature from July 6-8. No. 747 was put out on the 8th. 
It remained under the bell-jar till the 10th. Then free in 
the blazing sun. 
No. 752, similarly infected (but with better spores) on 
July 7, was put outside on the 10th. Its bell lifted on the nth 
and on the 13th free in the sun. 
Similarly with No. 7 54. Hence we must conclude either that 
the paper pulp method is bad, or that the temperature during 
incubation was so high that the mycelium in the leaf was 
killed. 
The weather during incubation was extremely hot — July 
10-21 — and several other seedlings were badly scorched when 
left under bell-jars, and the suspicion arose that the plants 
may have got so hot that the Fungus could not withstand it, 
and its growth was inhibited. 
Of course it might be urged that there is the possibility 
that, after all, these species of Bromus are resistant — but if so 
why did B. mollis in 747 and 752 resist the B. mollis spores, 
or B. sterilis in 754 those of B. sterilis ? Previous experi- 
ments have shown over and over again that such a result is 
not to be looked for. 
