494 Freeman. — Experiments on Brown Rust of Brontes. 
that experimented with ; there is also the danger from foreign 
spores after the Brome seedlings expose their leaves to the 
air. Care in selection of spore material should reduce the 
former to a very small error. There is no control of the second 
condition, except in the selection of a place free from Bromes, 
if the plants are to be kept as nearly normal as possible, and 
this is essential. Since the pustules on an infected leaf in 
a great majority of cases arises in the immediate vicinity 
of the infection spot, there may be at least an indication 
when foreign contamination has taken place. Confusion is 
also possible with the uredos of other species of Puccinia 
growing on Bromes. Errors resulting in negative results, 
e. g. poor spore material or the presence of conditions which 
are unfavourable for germination and of which the limits and 
exact nature are as yet unknown, are less easy to detect, so 
that chief reliance is perhaps to be placed upon the positive 
results. 
