34 BULLETIN 1275, U. S. DEPARTMENT OF AGRICULTURE 
centages of infection. Turkish Rustproof (S. N. 267) has shown a 
high degree of resistance to both smuts, but the selection from 
Turkish Rustproof (S. N. 268) seems to be somewhat more sus- 
ceptible. 
The cultivated strains and varieties of Avena sterilis have shown 
a remarkable degree of resistance to both loose and covered smut. 
It is especially striking that such important commercial varieties as 
Burt and Fulghum (including Kanota) possess a very high degree 
of resistance to the smuts. On the other liand, it is noteworthy that 
the wild t}^pes and the closely related species A. ludoviciana are 
moderately susceptible to both Ustilago avenae and U. levis. 
RESULTS FROM AVENA STRIGOSA 
Four strains (S. N. 29, 76, 133, and 177) of Avena strigosa 
Schreb. were grown. In the experiments with Ustilago avenae, 4,824 
plants were grown and in those with U. levis 3,736 were grown. 
No infected plants were observed. Evidently all the strains used 
were highly resistant to both smuts. 
Mrs. Lucille K. Bartholomew, in her experiments with certain vari- 
eties of oats while in the Office of Cereal Investigations, succeeded 
in producing infection in a single plant of Avena strigosa (unpub- 
lished data) . There can be no question as to the identification of the 
plant, because it was only partially smutted. 
It is interesting to compare the results with those obtained by 
Vavilov (#0). He grew in his experiments four different strains 
of Avena strigosa and found that three were immune from Ustilago 
avenae. The fourth strain, however, had a considerable percentage 
of infection. He found that this strain differed genetically from the 
other three, as it would cross readily with the ordinary types of 
Avena. Stapledon (18) and Sampson and Da vies (15) record the 
occurrence of smut hi the Orkney Strigosa. It is evident that there 
are distinct strains of A. strigosa that are more or less susceptible 
to the smuts: These may all differ genetically, however, and may 
have the sativa type in their ancestry. 
GREENHOUSE EXPERIMENTS 
It is evident from the data presented that very great differences 
are found in the susceptibility of oats to Ustilago avenae and U. 
levis. In order to examine more closely the behavior of some re- 
sistant varieties, experiments were conducted in the greenhouse in 
1919, 1920, and 1921. Several of the most resistant varieties, to- 
gether with a number of extremely susceptible ones, were grown in 
these different years. The data are summarized in Table 8. 
An examination of Table 8 shows clearly that varieties highly 
resistant under field conditions have maintained their resistance when 
grown in the greenhouse. These varieties include Avena brevis (S. N. 
77 and S. N. 134); A. ludoviciana (S. N. 72); A. sativa var. Black 
Mesdag (S. N. 70 and S. N. 117); A. sterilis var. Burt (S. N. 175), 
var. Fulghum (S. N. 129 and S. N. 257), and var. Red Rustproof 
(S. X. 262); and y1. strigosa (S. N. 133). A. brevis (S. N. 77) and A. 
ludovicicma <S. \. 72) gave entirely negative results in the field, but 
in (he greenhouse experiments one plant of each was observed to be 
infected. 
