in the Bromes and their Brown Rust . 259 
In devising some way of killing any possible Uredo-spores 
attached to the paleae or caryopsis, a few obstacles occurred 
owing to the difficulty of wetting the dry ‘ seeds ’ and the 
small size of the latter. Perhaps now that we know the 
maximum temperature for the spores (see p. 269), the best of 
all antiseptic measures will turn out to be careful heating in the 
dry state : this point needs further examination. As matter of 
fact I got good results by heating the seeds to 65-70° C in 
water : they will not stand 80-85° C. The temperature of 
65-70° C appears to be quite fatal to all Uredo-spores. 
I attempted to get over the difficulty of penetration of the 
micropyle, &c., by putting the ‘ seeds ’ in various liquids — 
chloroform, carbolic acid, mercuric chloride, &c. — and placing 
in a quickly acting air-pump and exhausting rapidly. As 
Table III shows, some success results, but great care is 
necessary to avoid damaging the radicle. Possibly more 
success will yet be met with in a longer series of trials, but 
I got very good results with chloroform. On the whole, 
however, heating to 70° C seemed most satisfactory. 
5. Experiments on Temperature. 
It seems surprising that we know practically nothing about 
the temperature of a leaf in the sunshine, yet such appears 
to be the case. A few observations have been made by 
placing thermometers with their bulbs stuck in the tissues 
of fleshy plants, such as Cacti, & c. \ but these hardly bear on 
the question concerning leaves, though they give us an insight 
into the subject of the high temperatures plant-tissues generally 
may withstand. 
Again, Keeble’s experiments 2 only bear indirectly on 
what we are here interested in: moreover they refer to 
tropical trees. 
Darwin, in his admirable memoir on Stomata 3 , has one or 
two records of leaf temperatures in Tropaeolum , but he gives 
no observations showing what temperatures are reached by 
1 Ascherson, Bot. Zeit. 2 Ann. Bot., vol. ix, 1895, p. 59. 
3 Phil. Trans., 1898, vol. 190, p. 531. 
