250 
Journal of Agricultural Research 
Vol. XXV, No. 5- 
shows the results obtained. Plants showing types of infection o, 1, and 
2 are listed as resistant. A few of the more highly resistant plants of a 
number of the varieties and strains were transplanted to larger pots and 
grown to maturity, being crossed and selfed to obtain material for further 
work. 
An examination of Table II shows that one or more resistant plants 
were found in each of the varieties and selections. Considerable varia¬ 
tion apparently exists as to the number of resistant individuals to be 
found in these varieties and selections. This may be due in some cases 
to the relatively small number of plants which it was possible to study. 
The differences between such varieties and selections as Rosen, Abruzzes 
40-55, 40-56, 40-59, 40-48, and Star on the one hand, and Giant Winter, 
Henry, and Virginia on the other, probably represent varietal differences 
in the occurrence of resistant strains. It may be that a number of the 
strains of the latter varieties, when in the pure condition, are entirely 
susceptible, the small degree of resistance shown coming from cross 
fertilization with adjacent more highly resistant strains. It is, however, 
significant that such varieties as Rosen from Michigan, Abruzzes from 
North Carolina, and the spring ryes from Purdue University, all fairly 
pure varieties, show resistance. The data indicate that to some extent 
resistance is to be expected in all the varieties of rye now commonly 
grown. 
DISCUSSION 
The discovery of rye individuals resistant to leaf rust of rye is of 
considerable interest because of the lack of data or observations on 
disease resistance in this cereal. Although 68 selections of rye repre¬ 
senting about 17 of the principal varieties grown in this country were 
studied, no variety was found which was uniformly resistant. As rye is 
almost always cross-pollinated, this would be expected unless a variety 
was selected with rust resistance in view. On the other hand, all the 
selections studied showed at least a few resistant individuals. This 
indicates, at least in all the varieties studied and probably in others as 
well, that the factor or factors determining resistance have not been 
eliminated by the processes which selected varieties from the original 
parental stock. Rye varieties have been obtained largely by repeated 
selection of desirable types without precautions being taken to prevent 
cross pollination. As a result, the varieties are relatively few and ill- 
defined, differing mostly in ability to develop and yield well, and composed 
of many strains, at least so far as disease resistance is concerned. The 
differences shown between the various selections and varieties as to 
proportion of resistant individuals may be due to a difference in the 
number of the susceptible and resistant strains of which they may be 
considered to be constituted. The constant crossing and recrossing 
which must occur among these strains doubtless cause the number of 
resistant individuals to vary considerably, so that any one test is probably 
only a rough estimate. Before the exact degree of resistance in the varie¬ 
ties can be determined, it doubtless will be necessary to establish, if 
possible, a number of pure lines by repeated selfing and selection similar 
to the methods being employed with corn in this country. 
The data obtained are insufficient to justify drawing conclusions as 
to inheritance in rye of resistance to leaf rust. It is obvious that a num¬ 
ber of generations of breeding will be necessary before the genetic con¬ 
stitution of material of such complexity can be known with any degree 
