514 
Journal of Agricultural Research 
Yol. XXX, No. 6 
mosaic symptoms added, demonstrat¬ 
ing a distinction between these two 
diseases. Similar distinctions appeared 
in the other series. Usually more 
marked dwarfing resulted from these 
combinations than from the single dis¬ 
eases. 
CONTACT INOCULATIONS IN THE 
GREENHOUSE 
In order to ascertain whether the 
mere contact of the seed pieces, roots, 
and shoots of spindle-tuber plants with 
those of healthy plants would produce 
infection, seed pieces from diseased 
and healthy plants were planted to¬ 
gether in 10-inch pots imthe Washing¬ 
ton greenhouses during the winter of 
1922-23. The healthy plants were of 
three varieties, Green Mountain, Irish 
Cobbler, and Bliss Triumph. Each 
variety was represented by 14 healthy 
tubers which were split in two. One- 
half of each healthy Green Mountain 
and Irish Cobbler tuber was planted 
in contact with a spindle tuber Bliss 
Triumph seed piece, while a half of 
each healthy Bliss Triumph tuber was 
planted in contact with a spindle 
tuber Green Mountain seed piece. 
Here contact of freshly cut surfaces 
was not intimate, as in tuber grafting. 
The other healthy tuber halves served 
as controls and were planted in 8-inch 
pots. From the time of planting, 
January 5, 1923, until harvest, April 
12,1923, the forty-two 10-inch pots were 
covered with aphid-proof cages, while 
the control plants in 8-inch pots 
remained uncaged in the same green¬ 
house. 
Three observations during this ex¬ 
periment did not disclose any insects 
on the caged plants. On account of 
seed piece decay six of the healthy 
Green Mountains in 10-inch pots 
failed to produce tuber progeny. 
At harvest all tuber progeny from 
the contact healthy plants as well as 
from the control plants appeared 
normal, while the tuber progeny from 
the spindle tuber plants which had 
attained sufficient size for diagnosis 
were spindle-shaped. 
The second generation Irish Cobbler 
and Bliss Triumph plants were grown 
in the open field at Presque Isle, Me., 
and those of the Green Mountain 
variety in the Washington, D. C., 
greenhouse. In this generation 31 
Irish Cobbler tuber units, representing 
13 of the original contact half tubers 
(one half tuber being without tuber 
progeny), as well as the respective 
controls, were healthy. Spindle tuber 
progeny resulted from all the original 
spindle tuber plants. In the second 
generation 29 Bliss Triumph tuber 
units, representing 11 contact half 
tubers of the first generation and their 
respective controls, remained free from 
spindle tuber. One other contact half 
tuber and its respective control pro¬ 
duced spindle tuber plants (in the first 
generation in the greenhouse) possibly 
as a result of late season field infection 
the previous season. Two contact half 
tubers failed to produce tubers in the 
first generation because of seed-piece 
decay. Likewise, in the second gener¬ 
ation 22 Green Mountain tuber units, 
representing 11 half tubers of the first 
generation and the respective controls, 
failed to produce spindle tuber progeny. 
These observations confirm similar 
ones on the contact of mosaic and leaf- 
roll plants with insects excluded, where 
negative evidence was obtained. 14 
A similar experiment but without 
insect cages, was performed in the 
Orono, Me., greenhouse at about the 
same time. Here Bliss Triumph tubers 
that were healthy or with mosaic of 
several types, leaf-roll, or spindle 
tuber were planted in steam-sterilized 
soil, each in a 10-inch pot with a 
healthy Green Mountan tuber. There 
were two similar series, W and C, 
which were placed in separate rooms, 
the former in a warmer place than the 
latter. Planting was done in the second 
week of December, 1922. White flies 
(Asterochiton vaporariorum ) appeared 
in January on other plants in the same 
greenhouse and were cyanide fumi¬ 
gated on January 12 and 18. All but 
one of the Bliss Triumph plants had 
emerged from the soil by January 22,. 
and the last one and also the Green 
Mountains had emerged by February 
8. White flies were present again, on 
the C series this time, in February and 
later in April, and were cvanided each 
time. Frequent observations dis¬ 
closed no aphids at any time, in this 
o Schultz, E. S., and Folsom, D. Op. cit. p. 46-48, 54. 
EXPLANATORY LEGEND FOR PLATE 7 
A. —Mild mosaic (2) in a Green Mountain hill of a strain known to be entirely mosaic from 1916 to 1923, 
inclusive, compared with a rugose mosaic hill of the same variety (1). Photographed on Sept. 10, 1923, 
after the death of the rugose mosaic vine 
B. —Plants grown from the right-hand tuber of Plate 5, B. Photographed on Aug. 11, 1923. Mi 
mosaic is present. Compare with Plate 5, C 
C. —Plants grown from the left-hand tuber of Plate 5, B. Otherwise as for Plate 7, B 
