RUST RESISTANCE OF OAT VARIETIES. 13 
DISCUSSION OF RESULTS. 
The notes in Table I on the varieties which showed resistance to 
one or both rusts indicate that rust resistance is very specific and 
that a particular variety may be entirely susceptible to one rust and 
somewhat resistant to the attacks of another. 1 
Of the 122 strains tested, 80 unquestionably were susceptible to 
both rusts in both stages of growth. This does not imply that these 
varieties are not of great commercial value in other respects and is 
not sufficient reason for discarding them from cultivation, for at 
present there are no suitable varieties to substitute for the best of 
them. It probably does remove them, however, from the list which 
is to afford promise of rust-resistant varieties. Heavy infections 
were obtained on practically all of these, and at least some normal 
uredinia were formed on all. While such greenhouse tests do not 
represent field conditions accurately, the optimum conditions for 
infection provided should make the evidences of resistance which 
appeared in some varieties all the more valuable. Some of these 
varieties may show some resistance under field conditions and some 
of them have properly been recommended as rust-escaping because 
of their early-ripening habit, as, for instance, the Sixty-Day and 
Kherson varieties. 
In 80 out of the 122 cases the results at two distinct periods in the 
life of the host plant have led to identical conclusions as to the sus- 
ceptibility of the variety. In some of the resistant varieties, also, 
both seedlings and mature plants gave the same evidences of re- 
sistance, though the results are not always in agreement. These 
susceptible varieties need not be discussed in further detail, but the 
list includes the following commonly grown sorts: American Ban- 
ner, Big Four, Ligowo, Lincoln, Siberian, Sixty-Day, Swedish 
Select, and White Russian. In this list are included also most of 
the botanical species represented and nearly all of the recently intro- 
duced foreign varieties. 
In the Arena sterilis group also, where most of the resistance to 
crown rust is found, several strains are very susceptible to the crown 
rust, as, for instance, Greenhouse No. 296, Red Algerian, and one 
strain each of Golden Rustproof, Italian Rustproof, Red Rustproof, 
and Turkish Rustproof. 
Not all varieties of the Arena sterilis group show perceptible re- 
sistance to either rust, and great care should be exercised in recom- 
mending to farmers these or other varieties as rust resistant. Still 
greater care is necessary in choosing a strain to use as a parent 
1 The studies of these varieties indicate the necessity for selecting and working from 
individual plants, for certainly within the same variety, and even within a line supposed 
to be pure for other characters, differences of a major degree in rust resistance exist. 
