in the Bromes and their Brown Rust. 291 
pulp obtained by scraping sterilized filter-paper. In all cases 
the tested spores gave good and in some cases excellent 
results as regards germination. 
The infection was made under wet beakers, as usual, and 
the plants left thus at the west window for two days. Then 
they were put outside under bell-jars, and freed from these 
on the fourth day, and placed fully exposed to the sun, the 
pots standing in saucers and kept properly watered. 
The temperature on July 6 to 13, the week of inoculation 
and infection, was high, the maximum being about 29° C and 
the minimum I5°C in the shade, and in the west window 
between 3 and 6 p.m. it would occasionally be higher, though 
a shade blind is always used there. 
It is to the high temperature, I think, that the delay or 
failure of infection and incubation must be attributed. The 
question arises how far the failures are due to it alone. In 
considering these failures we must not forget that each pot 
in each series received the same treatment, however, so that 
we still have comparative results. 
Nevertheless it seems significant that rain brought down 
the temperature of July 7 to about T4-20 0 C from i 6-30°C 
the minima and maxima of July 6 . On July 8 the tempera- 
ture rose again. It was these series which directed my atten- 
tion more particularly to the question of temperature, and no 
doubt much work will be needed before its full importance in 
infection is understood. When we find that the thermometer 
registers 38-36° C in the sun, and that (see Table X, p. 270) 
the spores will not germinate much above 25° C, it seems likely 
that the young mycelium in the leaf will also be inhibited by 
the high temperatures, though we are ignorant of what the 
exact temperature inside the leaf may be. 
In view of the evident failure of Nos. 747 and 754 it seemed 
necessary to examine somewhat more closely what conditions 
could be supposed to have affected the matter. Three points 
are concerned : the germination of the spores, the infection, 
and the incubation periods. 
The spores were tested and were known to be vigorously 
