26 o 
Journal of Agricultural Research 
Vol. XXV, No. 6 
and that in the third season. No record was obtainable of the disease 
status of this sample previous to 1919. 
Referring now to the other condition mentioned previously—namely, 
that in which there seemed to occur a marked increase in seriousness 
of infection from one season to the next, the following cases are cited: 
(a) It was observed in plants just emerging from the soil in the green¬ 
house bench that certain ones exhibited marked wrinkling and mottling 
of leaves at this early stage (PI. 2, B and C), while others, which later 
developed typical though mild mosaic symptoms, showed no mottling 
or wrinkling at the corresponding period of development (PI. 2, D). The 
plants shown in Plate 2, C and D, are both from parentage indicated as 
mild mosaic but not from the same hill. ( b ) Again, a case of extreme 
mosaic is observed in a very young plant which is from a parentage 
indicated as “healthy but adjacent to mosaic hills” (PI. 2, B). 
In Plate 2 the potted plants A, 1 and A, 2 are grown from the same 
corresponding tubers as the plants shown in C and D. A, 1 and C from 
the same tuber developed early the extreme type of mosaic from mosaic 
mild ancestry, while A, 2 and D developed mild mosaic symptoms from 
an ancestry exhibiting the same type of infection. 
The writer has at hand no definite evidence upon which to ‘base an 
explanation of the differing types of mosaic infection just described. 
There may be some weight accorded to the suggestion that certain 
plants possess a factor of resistance to mosaic infection which is absent 
in other plants. It is also conceivable that the divergencies in the type 
and seriousness of symptoms observed may be due to differences in 
amount of infective material introduced by aphids or other agencies. 
Another and perhaps more plausible explanation is that in the plants 
exhibiting the mild and extreme symptoms, there may occur what are in 
effect distinct types or strains of mosaic possessing sufficient individuality 
to account for the persistence of either through successive generations 
of the host plant. The sudden development of the extreme type in 
such plants as are illustrated in Plate 2, B, and the continuation of the 
mild type in Plate 2, D, may be considered as furnishing some support 
for this argument. It is to be hoped that further investigations will 
throw light upon this point. 
SPINDIylNG-SPROUT AND EEAFROLIv 
In 1916 Stewart (13, p . 331) in a discussion of the results of his “Obser¬ 
vations on Some Degenerate Strains of Potatoes,” summarizes his 
conclusions in part as follows: “Although spindling-sprout symptoms 
appeared occasionally in the tubers of plants affected with mosaic, leaf- 
roll, and curly-dwarf, they were too infrequent to warrant the conclusion 
that spindling-sprout is correlated with any of these three diseases.” He 
further adds, “sprouting tests of tubers from leafroll, curly-dwarf, and 
mosaic plants show that spindling-sprout is not a symptom of these 
diseases.” In general, the present investigation has shown that 
spindling-sprout, while it is not, as a rule, a symptom of curly-dwarf or 
mosaic, is a consistent symptom of leafroll and often also of net-necrosis. 
Stewart's procedure in noting the sprout condition of tubers from plants 
of certain observed foliage symptoms of the previous season, seems to 
the writer to be not so dependable with reference to the information 
sought as that which takes into account as well, and indeed, primarily, 
the foliage condition of the progeny plants. It must frequently occur 
