in ike Bronzes and their Brown Rust. 273 
antagonism must be due to something far more subtle than 
a mere soluble poison oozing from the cells, 
7. Methods of Infection. 
The methods employed for the principal series of compara- 
tive infections were as follows. 
The carefully selected ‘ seeds ’ of the Bromes were sown in 
new pots of fresh soil, generally a dozen to a score in a pot, 
and allowed to germinate under hand-glasses till about a week 
old. The pots were then placed under bell-jars, kept moist by 
filter-paper, and put in a west window in the laboratory for 
24-48 hours, until the first green leaf (morphologically the 
second leaf) was well developed. During this period the 
‘ spear,’ enveloped in the first morphological leaf, which con- 
sists of the sheath only, exudes copious drops of water from 
the clefts corresponding to water-stomata at its apex. 
In some cases I infected the seedlings by putting spores on 
these ‘ tip-drops ’ : in others I placed the spores on the flat 
face of the leaf. It remains to be seen how far differences in 
results depend on these differences in procedure, as also whether 
anything depends on the different distribution of the stomata 
on the front and back of the leaf. The investigations of all 
these points in detail will require some time, but at present 
the evidence seems to show that it is immaterial, and that 
the infecting tubes can pass even into the slits representing 
water-stomata at the extreme tip. 
In any case it is certain that the ‘ spears ’ are susceptible of 
infection when only two or three mm. high, and long before 
the first green leaf is expanded, a point of some importance in 
discussing the question of the infectivity of seedlings. 
In other cases I infected older seedlings at the base, apex, 
or intermediate parts of the second or third leaf, and one or 
two curious points arise in this connexion. 
Infection may apparently fail at the base of rapidly growing 
young leaves, either because the stomata are not fully developed 
there, or because the rapidly elongating tissues pass forwards 
before the tips of the germ-tubes can gain an entrance. 
