RUST RESISTANCE OF OAT VARIETIES. 5 
tain that the same number of spores was applied in each case. The 
time of appearance, size of uredinia, and character of infection are 
deemed of greater importance. 
The seedling plants were discarded as soon as final notes were ob- 
tained. Those in the series inoculated at the time of heading were 
allowed to mature in order to obtain herbarium specimens and seed 
for further work. 
SOURCES OF MATERIAL. 
The seed of all the varieties tested except Early Ripe 1 was ob- 
tained from the 1915 crop grown in rod rows in the rust nursery at 
Ames, Iowa. Most of these varieties were secured from Mr. C. W. 
Warburton, of the Office of Cereal Investigations, Bureau of Plant 
Industry; others were obtained from the Minnesota Agricultural 
Experiment Station. The forms listed under the Latin (specific) 
names (greenhouse Nos. 265 to 303) were obtained from Director 
Bubak, of the botanic garden at Tabor, Bohemia, through Prof. G. 
M. Eeed, of the University of Missouri. 
None of these varieties may properly be called a pure line, although 
some of these rows are traceable (several seasons back) to single 
plants. Others represent bulk material from rod rows, field plats, 
or commercial seed stocks. Some of the foreign material is in great 
need of more careful classification. Mixtures in the previous han- 
dling of both the domestic and foreign material sometimes have 
occurred, but it may be said safely that a majority of the varieties 
were true to name and for the most part pure, so that where eight 
or more seedlings were studied most of them really represented the 
true type of the variety under the name of which they were grown. 
In the trials on older plants, however, where only two individuals 
were studied, slight mixtures of the seed sample were more serious. 2 
EVIDENCES OF RUST RESISTANCE IN CEREALS. 
Before proceeding to a detailed description and consideration of 
the observations made and conclusions drawn it will be well to refer 
to the observations of earlier wurkers on rust resistance in cereals. 
Cobb (3) described certain wheat varieties which were resistant 
and mentioned the occurrence of dead areas of host tissiie. Marryat 
(6) also observed these dead areas in immune varieties, and Biff en 
(1) mentions unopened pustules which shed no spores. Stakman 
(12) observed similar indications of real resistance on (a) seedling- 
leaves of certain wheat varieties and on (b) leaves of a wheat sus- 
ceptible to the stem rust of wheat but inoculated with the stem rust 
of oats. He states that the more resistant a form proved, the more 
pronounced was the tendency of the rust to kill small areas of the 
1 Seed of this variety was obtained from Dr. H. H. Love. It is very similar to Burt 
and perhaps identical with that variety. Evidence tends to show that the origin of the 
two varieties was the same. 
2 All such instances are indicated in Table I. 
