56 
A large amount of additional work has been done along this 
line. Numerous collections of both loose and covered smut from 
various regions have been received and these have been tested 
upon a few varieties of oats. Several of the collections have 
behaved in the same general manner but it is possible that 
differences in behavior would appear if a wider range of hosts 
was used. A few of the smut collections, however, indicate 
distinct new races limited in a definite manner to certain par- 
ticular varieties. Perhaps the most interesting one is that which 
appears to be capable of attacking Fulghum oats, a variety 
which has proved quite resistant to the other races. It is also 
worthy of note that the variety Black Mesdag has proved to be 
highly resistant to all of the races so far studied. 
The occurrence of these specialized races is particularly 
important in problems of plant breeding and we must recognize 
the fact that there are distinct races of smut capable of being 
separated on the basis of their ability to infect different varieties 
of oats. A particular variety of oats may be resistant to one or 
more races but susceptible to another and progress in breeding 
can only be made when these possibilities are taken into account. 
Extensive data have been ‘published on the problem of the 
inheritance of resistance of certain oat hybrids to loose smut, 
Ustilago avenae. The data presented were derived from a cross 
involving the very resistant Black Mesdag and the very sus- 
ceptible Avena nuda var. inermis, and the behavior of their 
progeny to the Missouri specialized race of smut. The two 
parents differ in several important respects. Black Mesdag 
belongs to the Avena sativa type. It isa hulled oat with black 
flowering glumes, numerous awns and two or occasionally three 
flowers to the spikelet. On the other hand, Avena nuda var. 
inermis is a hull-less or naked oat with light colored glumes, 
without awns, and containing four or more flowers in each 
spikelet. The results described involved inoculation experi- 
ments with the Fe, F; and, to some extent, the Fs generation of 
hybrids. The general results indicate that resistance to the 
smut in this cross is dominant, while susceptibility is recessive. 
The facts are also in close accord with the interpretation that 
there is a single factor difference between the two parents. 
Some attention was paid to the inheritance of various morpho- 
