36 BULLETIN 1275, U. S. DEPARTMENT OF AGRICULTURE 
and var. Green Mountain (S. N. 110). On the whole, the percentages 
of infection were somewhat higher in the greenhouse than m the field. 
Certain varieties, Avena ludoviciana (S. N. 180) and A. sterilis 
var. Red Rustproof (S. N. 262), gave negative results in the green- 
house cultures, although infections usually occurred in the field. 
Moderately resistant varieties, such as A. sativa var. Black Diamond 
(S.N. 116), var. Ruakura Rustproof (S.N.266), andyar. Belyak (S.N. 
306) , gave about the same percentages of infection in the greenhouse 
as in the field trials. Danisn Island (S. N. 3 1 1) , which under field con- 
ditions showed only slight susceptibility to the smuts, gave rather 
high infections with Ustilago avenae in the greenhouse. 
A special feature of the greenhouse infections was the vi^or of the 
outbreak of the smut. In many cases the spores were developed not 
only in the floral parts but also on the upper leaves of the plant, 
resembling a characteristic leaf smut such as Urocystis tritici on wheat 
or Ustilago striaeformis on various grasses. In most cases these sori 
were found only on the upper or flag leaf; sometimes, however, one 
or more of the leaves just below the flag leaf also showed the same 
condition, but as a rule the sori on these were not so prominent nor 
extensive. These linear sori occurred on the blade of the leaf, rarely 
on the upper part of the sheath. The pustules were most numerous 
at the base oi the blade, but frequently extended clear to the tip, 
forming long parallel striae. In the early stages the spore masses were 
covered by the leaf tissue which soon ruptured and allowed the spores 
to escape. Very often the leaf, if severely attacked, was dwarfed. 
(Pis. II and III.) Several observers (3,9) have recorded this occurrence 
of the formation of spores on the leaves, and Verissimo d' Almeida and 
de Souza {21) have described a variety foliicola of Ustilago avenae. 
While this condition seems to be more prevalent in plants grown 
under greenhouse conditions, occasionally a similar condition is 
observed in plants grown in the field. 
These leaf sori occur on plants infected both by Ustilago avenae and 
U. levis. Their occurrence seemed to be correlated somewhat with 
the susceptibility of the varieties. The strains of Avena fatua, A. 
nuda,snia A. sativa orientalis var. Green Mountain were particularly 
conspicuous for the development of these sori on the leaves. 
SUMMARY 
Studies on the varietal resistance and susceptibility of oats to 
Ustilago avenae (Pers.) Jens, and U. levis (K. and S.) Magn. were 
carried out at Columbia, Mo., Ames, Iowa, Manhattan, Kans., 
Aberdeen, Idaho, Pullman^ Wash., and Brooklyn, N. Y. Strains 
and varieties of Avena brevis Roth, A. fatua L., A. ludoviciana Dur., 
A. nuda L., A. sativa L., A. sativa orientalis L., A. sterilis L., and A. 
strigosa Schreb. were grown. 
The strains and varieties at the widely separated stations gave, in 
general, similar results. 
Six strains of Avena brevis were grown. Five of these wore similar 
and gave negative results with both smuts, except in one doubtful 
case. Plants grown in the Ustilago avenae series numbered 4, .*->'.»(). 
and in the U. levis series they numbered 3,734. The remaining strain 
differed in maturing later and in other respects. Only four plants 
out of a total of 1,0 16 were observed to be infec ted with U. levis. Nega« 
