Mar. 15, 1925 
Degeneration Diseases of Potatoes 
523 
duration of certain insects known to be 
capable of the transmission of these 
diseases. In order to secure additional 
evidence regarding the effect of different 
regions on the dissemination of mosaic, 
leaf-roll, and spindle tuber, the follow¬ 
ing test was carried on. 
In 1922 comparatively healthy com¬ 
mercial stocks of five varieties, Green 
Mountain, Rural New Yorker, Rose 
Four, Irish Cobbler, and Bliss Triumph, 
were grown in four regions: On Aroos¬ 
took Farm in northeastern Maine, on 
Highmoor Farm in southwestern Maine, 
at Riverhead, Long Island, and at Nor¬ 
folk, Va. In each variety one original 
stock was selected and divided into ten 
30-pound lots. Two such lots of each 
variety were planted in each locality, 
one lot between rows of Green Moun¬ 
tains with 100 per cent both mosaic and 
spindle tuber and the other lot between 
rows of Irish Cobblers with 100 per cent 
leaf-roll and the same per cent spindle 
tuber. In addition, at Riverhead and 
Norfolk a third lot of each variety was 
grown several rods from any 100 per 
cent diseased stock. The diseased Green 
Mountains also were originally from 
one lot which was divided for planting 
in the four regions; the same is true of 
the diseased Irish Cobblers. In 1922 
representative samples of the 50 differ¬ 
ent healthy lots and of the diseased lots 
were kept, and in 1923 were grown on 
Aroostook Farm, where the observations 
recorded in Table XI were made. 
The data in Table XI can be used 
for several kinds of comparisons. Mild 
mosaic was present in about 20 to 30 
per cent of the hills in the Green Moun¬ 
tain lots from between leaf-roll Irish 
Cobbler rows in the four regions, and 
from the isolated lots not grown be¬ 
tween diseased rows. Relative to the 
preceding, there was a somewhat 
higher percentage in the Green Moun¬ 
tain lots from between mosaic Green 
Mountain rows in northeastern Maine 
and southwestern Maine, and still 
more from the same in Virginia and 
Long Island. Mild mosaic was present 
in about 30 to 40 per cent of all the 
Bliss Triumph lots except a very small, 
unrepresentative one where 3 of the 
5 plants were leaf-roll. Mosaic, that 
is not of the rugose type, probably was 
present in the lots of the other varieties 
originally, and was unusually con¬ 
spicuous in 1923 when present. Except 
where masked by rugose mosaic, it was 
present in about 30 to 50 per cent of the 
hills in the Rural New Yorker lots, in 
about 10 to 20 per cent of the Irish 
Cobbler lots, and in about 30 to 60 per 
cent of the Rose Four lots. Therefore, 
with these types of mosaic there was no 
marked difference between different 
regions or between different plots in the 
same region. 
Rugose mosaic, however, was much 
more abundant in the Virginia lots than 
in the corresponding ones from other 
regions, in each variety and in all three 
locations in the field relative to dis¬ 
eased rows. The only exception is in a 
small lot of three plants, which is 
negligible. Rugose mosaic was present, 
though in small percentages, in a ma¬ 
jority of the lots from northeastern 
Maine and Long Island but was absent 
from most of the lots from south¬ 
western Maine. It was present in all 
Irish Cobbler lots except one, though 
this variety showed the lowest per¬ 
centages, and absent from all Rural 
New Yorker lots except those from 
Virginia. Therefore rugose mosaic 
was contracted only slightly in south¬ 
western Maine but markedly in Vir¬ 
ginia, and was contracted by different 
varieties in different amounts. 
Leaf-roll was in 100 per cent of 
every Virginia lot from between leaf- 
roll Irish Cobbler rows (pi. J.0, A) and 
for the lots from Long Island ranged 
from 51 to 93 per cent (pi. 10, B), from 
southwestern Maine from 0 to 60 per 
cent (pi. 10, C), and from northeastern 
Maine from 0 to 22 per cent (pi. 10, D), 
with averages respectively of 74, 26, 
and 6 per cent. It is clear that the 
spread of leaf-roll was greater as the 
region was farther south. Farther 
spread than from diseased rows to 
adjoining healthy rows occurred in 
Virginia and Long Island but not in 
either part of Maine. In Virginia the 
Green Mountains and Bliss Triumphs 
between the mosaic Green Mountain 
rows contracted over 90 per cent 
leaf-roll, and where grown a few rods 
from 100 per cent diseased rows con¬ 
tracted over 80 per cent in that region. 
Where there was a difference among 
the varieties Green Mountains and 
Bliss Triumphs generally were the most 
infected by leaf-roll. 
Spindle tuber was originally in 100 per 
cent of the hills in both the diseased 
Green Mountain lots, the diseased 
Irish Cobbler lots, and the “healthy” 
Rose Four lots. The last will be 
disregarded in the comparisons to be 
made. From between the Green 
Mountain rows the Virginia lots 
ranged from 68 to 92 per cent spindle 
tuber, the northeastern Maine lots 
from 30 to 90 per cent, the Long Island 
lots from 4 to 78 per cent, and the 
southwestern Maine lots from 4 to 38 
per cent, with respective averages of 
85, 54, 39, and 16 per cent. From 
between the Irish Cobbler rows the 
