VARIETAL SUSCEPTIBILITY OF OATS TO SMUTS 5 
Vavilov 's results coincide very closely with those obtained by the 
senior writer. The resistant and susceptible strains and varieties 
are similarly distributed among the different species. It is especially 
interesting that the only immune variety of Avena sativa (A. diffusa) 
observed by Vavilov is Mesdag, which appears to be identical with 
the variety Black Mesdag which proved so free from smut in the 
experiments of the senior writer. In his field experiments Vavilov 
found this variety entirely free from smut, but under greenhouse 
conditions he was able to obtain an occasional smutted plant. Vavi- 
lov also records resistance to loose smut in A. nuda var. biaristata. 
This variety, unlike the other varieties of A. nuda investigated, is 
characterized by 14 to 16 chromosomes. Vavilov also records that 
one strain of A. strigosa proved to be susceptible to loose smut. This 
strain, however, also is genetically different from the ordinary races of 
this species and can be readily crossed with varieties of A. sativa. 
Stapledon (18) has noted the prevalence of smut in the varieties 
of oats at the Welsh Plant Breeding Station at Aberystwyth. His 
results are much more significant on the question of contamination 
of seed than on the problem of varietal resistance. It should be 
noted, however, that Welsh Strigosa, belonging to the Avena strigosa 
group, produced some smutted plants. 
Sampson and Davies {15) have recorded the occurrence of TJsiilago 
avenae on 31 varieties in the experimental plats at Aberystwyth, 
Wales. Fifteen of these, among them the varieties Culberson, Black 
Mesdag, Golden Rain, and Black Mogul, appeared to be quite 
susceptible. According to these investigators, U. levis is rare in 
Wales, having been found in the experimental plats only on Avena 
nudaYSLT. cMnensis and A. strigosa subspecies glabrescens smdorcadensis. 
They carried out an experiment in which they inoculated eight 
varieties of oats with spores of U. levis from Orkney Strigosa. They 
obtained infection on Orkney Strigosa, but the other seven varieties — 
Algerian Sterilis, Welsh Strigosa, Ceirch du Bach, Black Tartar, 
Golden Rain, Radnorshire Sprig, and Potato — gave negative results. 
However, according to their other records these varieties are infected 
severely by U. avenae. 
In comparing the results of Sampson and Davies with those pre- 
viously obtained by the senior writer, the most important difference 
is the occurrence of smut on Black Mesdag and the different varieties 
of Avena strigosa. It is not unlikely that different strains of certain 
varieties of oats may vary in their susceptibility to smut. The 
senior writer has received from the Welsh Plant Breeding Station 
its varieties of A. strigosa and has found that they are quite different 
in appearance from those with which he has worked. It is evident 
that there are varieties and strains of A. strigosa which are susceptible 
to oat smut and others which are highly resistant. 
CHARACTERISTICS OF THE OAT SMUTS 
There are two distinct species of smuts which attack oats — the loose 
smut, Ustilago avenae (Pers.) Jens., and the covered smut, U. levis 
(K. and S.) Magn. The principal morphological distinction be- 
tween them is found in the character of the spores. The spores of 
loose smut are minutely echinulate, while those of the covered smut 
are entirely smooth. The spores of both are about the same size 
and shape and are somewhat lighter colored on one side. 
