in the Bromes and their Brown Rust. 261 
A third thermometer was hung vertically in the air, well 
away from the thin glass rod which supported it by a thread, 
and which was stuck in a pot of soil. 
A fourth thermometer with blackened bulb was similarly 
suspended from another thin glass rod. 
And, finally, a similarly suspended thermometer with a 
long but narrow thin bulb — one of those which I use for 
inserting into glass cells in which hanging drops are cultivated 
— was so arranged that the bulb was wrapped in the broad 
leaves of B . maximus , and thus protected from the direct rays 
of the sun by the thickness of a single leaf. 
Various readings were taken on different days, of which 
the following may be given (Tables IV, V, and VI). It is 
not claimed that this method gives perfectly accurate results, 
but it shows quite clearly the kind of temperatures which 
may be expected in the closed glass vessels in which the 
spores are put to germinate on the leaves ; and even if it is 
contended that it will not give the exact temperature of the 
leaf-surface on which the spores are sown, we may fairly 
assume that it does show an approach to it, and at any rate 
demonstrates that such leaves may be heated up to tempera- 
tures far above the maximum for spore-germination or that 
which the germ-tubes can withstand, without themselves being 
damaged. 
I am of opinion that more accurate records with a ther- 
mopyle will show that the leaves in direct sunshine are 
heated up to temperatures far higher than is usually assumed. 
6. The Germination of the Uredospores. 
The germination of the spores — Uredo-spores — is as a rule 
easily brought about in water, distilled or tap water, but 
many observers have remarked the curious uncertainty some- 
times met with in their behaviour. I have paid some atten- 
tion to this matter, with a view to discover if possible what 
are the conditions which dominate the capacity for germina- 
tion. 
In a good batch of spores, signs of germination in water 
