30 
BULLETIN 64, U. S. DEPARTMENT OF AGEICULTUEE. 
The sharp differentiation between healthy and diseased varieties 
in adjacent rows, and other field evidence, indicates that the leaf- 
roll and curly-dwarf are manifestations of physiological weakness 
and associated with decline or loss of vigor of the strain. That 
certain varieties show a greater tendency to such degeneration 
phenomena is evident, and the still more marked development of 
these troubles on certain seedlings emphasizes their relation to the 
varietal problem. That many other seedlings in the same field 
exhibited unusual health and vigor seems convincing evidence that in 
this seed selection and breeding the way lies open for the complete 
solution of this problem of leaf -roll control. 
Of 59 of these diseased seedlings selected at random as typical 
examples in 1912, 29 were affected with leaf-roll and 30 with curly- 
dwarf; and of 22 selected in 1913, 7 had leaf -roll and 15 had curly- 
dwarf. The parentage of these is indicated in Table I, for its bearing 
on the question that will be asked as to whether certain combinations 
of varieties have a tendency to produce leaf-rolled or curly-dwarfed 
offspring. 
Table I. — Parentage of diseased seedlings. 
Parent varieties. 
Geheimrat Theil X Keeper 
Sophie X Keeper 
President Kriiger X Keeper 
Delaware X Keeper 
Norcross X Keeper 
Gem of Aroostook X Keeper 
Alexander's No. 1 Red X Keeper. 
Round Pinkeye X Keeper 
Irish Cobbler X Keeper 
Green Mountain X Keeper 
Keeper X Round Pinkeye 
Keeper X Silverskin 
Sophie X Irish Seedling 
Delaware X Round Pinkeye 
Number 
diseased with- 
Leaf- 
roll. 
Curly- 
dwarf. 
Parent varieties. 
Apollo X Silverskin 
Gem of Aroostook X Round Pink- 
eye 
Daisy X Keeper 
Early Eureka X Keeper 
Holborn Abundance X Irish Seed- 
ling 
Alexander's No. 1 Red X Irene. . . 
Manly X Irene 
Garnet Chili X Silverskin 
Irish Cobbler X Irish Seedling. . . 
Apollo X Irish Seedling 
Total. 
Number 
diseased with- 
Leaf- 
roll. 
36 
Curly- 
dwarf. 
A much more detailed analysis of the characteristics of these 
varieties and their seedlings is really required to answer this question. 
It is clear, however, that some varieties, like Keeper, are poor parents. 
A large number of successful crosses with Keeper were secured by 
Prof. Stuart because it produced an abundance of pollen, but the 
offspring of these have been so unsatisfactory on account of their 
tendency to curly-dwarf and leaf-roll that the variety will not be 
used again for crossing. 
From different crosses having the same varieties as parents 
there have come seedlings, some of which were leaf-rolled and some 
curly-dwarfed. No. 16472, illustrated in Plate IV, figure 1, is a 
perfect type of leaf -roll in a cross between Alexander's No. 1 Red and 
Keeper, while No. 16503, shown in Plate XI, figure 1, is an equally 
