710 
Journal of Agricultural Research 
Vol. XXVIII, No. 7 
INVESTIGATIONS 
Two distinct experiments were conducted. In the first a single rust, collected 
at Berkeley, Calif., was used. In the second, nine different collections of rust, 
from as many localities in the State, were used for inoculations. 
EXPERIMENTS WITH ONE RUST IN GREENHOUSE AND FIELD 
The varieties of oats tested were obtained from the following sources: 
Varieties 
United States Department of Agriculture______140 
California Agricultural Experiment Station....... 36 
Washington Agricultural Experiment Station..... 26 
Iowa Agricultural Experiment Station..... 14 
Kansas Agricultural Experiment Station...... 1 
Total.......... 217 
The lists included duplicates of many of the varieties. Some of the plants 
bearing the same name were very similar morphologically, but others differed 
somewhat. All were included in the tests. In other cases, plants bearing 
different names were alike. Etheridge’s “Classification of the Varieties of 
Cultivated Oats” (3) was used in studying the material and any changes that 
were made in the names w r ere in conformity to his descriptions. Each change 
in the name of a variety is recorded. 
The oat stem rust used in 1920 to obtain the results shown in Table I was 
found growing on cultivated oats in the botanical garden at Berkeley in the 
winter of 1919-20. It was cultured on red oats in the greenhouse. Square 
paper pots were placed in flats holding four rows of pots, with 10 in each row. 
Each variety occupied one row in a flat, a single seed being sown in each of the 
10 pots. As the available greenhouse space was not great enough to accom¬ 
modate all of them at once, they were grown in successive lots. The seedlings 
were inoculated when they were about 10 days old and were kept in a damp 
chamber 48 hours. After tw r o w r eeks the rust was studied and recorded, and 
the rusted leaves were packeted, labeled, and pressed. The seedlings were then 
transplanted to plats in the botanical garden. The first lots were set out on 
the seventeenth of February and the last on the twenty-seventh of March. The 
series was then repeated, the second set being about six weeks later than the first. 
When half grown these plants were subjected to a heavy artificial epidemic 
of the same rust. For this purpose urediniospores w T ere grown in the greenhouse. 
These spores were put into tap water and applied to the plants either by the 
use of an atomizer or by rubbing the culms with moistened fingers. As the 
epidemic developed on the older plants spores were transferred by the same 
method from the older to the younger plants. When nearing maturity, rusted 
specimens of each variety (including at least one complete culm) were studied, 
recorded, packeted, and pressed. Thus, each variety was subjected to four rust 
tests, two in the greenhouse and two in the field. The rust was measured on a 
scale of 0 to 4, in wdiich 0 is immunity and 4 is complete susceptibility. 
Eriksson and Henning (.£), in “Die Getreideroste” (1896), used in their tables 
a scale of 1 to 4 for grading rust. Rust-free material was recorded in a column 
headed “rein,” 1 indicated traces of rust, 2 and 3 larger amounts, and 4 abundance 
of rust. Their estimates w'ere based largely on the quantity of rust found. 
As used in this paper, the scale of 0 to 4 is not based on quantity of rust but on 
the size and appearance of individual uredinia. The types of infection as defined 
