RELATION OF SOME RUSTS TO THEIR HOSTS 1 85 
coronata was employed wherever oats (Avena sativa L.) could be used 
advantageously, and whenever time allowed. These two rusts were 
kept going on their host plants and thus stock material was always on 
hand. The method used was to make a spore suspension of the uredo- 
spores and spray them on the host by means of an atomizer. The 
pots were then covered with a bell jar and placed where the temperature 
ranged between 14° and 25° C, a temperature of 20° C. being used 
whenever obtainable. The belljars were removed after 24 hours. 
When maize was used it was found to be advantageous to draw the 
leaves gently between the fingers before inoculating as the leaves are 
covered with a wax-like substance which causes the spore suspension 
to roll off without wetting them. In some experiments, definite areas 
were inoculated by placing spores on them with a spear-pointed needle 
after the plant had been atomized. During the winter, the cultures 
were kept in a greenhouse, where Puccinia coronata required renewal 
about every three to five weeks and Puccinia Sorghi about every two 
months. This was done by inoculating freshly grown plants. During 
the summer, the stock cultures were kept in a garden in the open, 
where the rusts propagated themselves. 
Development of the Rusts 
Puccinia coronata 
The first signs of infection show in from five to seven days after 
inoculation, when light green areas are formed on the leaves. About 
seven to eleven days after inoculation, pustules appear in these areas 
as small, yellowish swellings, which soon break through the epidermis 
liberating the mass of uredospores. Teleutospores develop in about 
twenty-nine to thirty-six days after inoculation, when uredospore 
production has about ceased and the leaf is slowly dying and drying up. 
They show as blackish zones usually at the margins of the infected 
areas and their first appearance occurs towards the apex of the leaf, 
which is also the part of the leaf which first begins to die. 
Puccinia Sorghi 
The first signs of infection on maize are also light-colored areas on 
the leaves. These appear in about six to seven days after inoculation 
and pustules develop soon afterward, in usually seven to ten days. 
