24 
Journal of Agricultural Research 
Vol. XIV, No. i 
of blight. The plants left as controls appeared healthy. These results 
indicate that spinach-blight is caused by a definite virus, and is trans¬ 
mitted from plant to plant by the aphids. 
COMPARISON OF DISEASED MATERIAL FROM VARIOUS LOCAL SOURCES 
Farm C.—Diseased plants collected in two blighted areas on farm C 
were placed in a field cage, care being taken that the blighted plants 
did not touch the healthy spinach seedlings in the cage. Both species 
of aphids were present on the blighted plants. Sixty-one days later 
two of the seedling plants had developed the mottled leaves typical of 
spinach-blight. Twelve days later a third seedling plant developed 
definite symptoms of blight. 
These results indicate that the aphids on introduced, blighted plants 
had crawled to the seedling plants and had infected them with the 
spinach-blight virus. 
In order to prove the infection, one mottled leaf was removed from each 
of two diseased plants for prick inoculations. With a flamed needle 
the leaves of two spinach plants were pricked to serve as controls. Seven 
plants in two pots were inoculated by pricking through the mottled leaf 
of plant i into the healthy leaf of the seedling. Seven similar plants 
in two pots were inoculated by pricking into them the juice of the mottled 
leaf from plant 2. Twelve days after inoculation five plants developed 
typical symptoms of blight. Thirty-six days after inoculation 12 of the 
14 inoculated plants had developed the mottled leaves characteristic of 
blight, but the control plants were large and apparently healthy. The 
other inoculated plants, although not showing typical symptoms of blight, 
did not have the healthy appearance of the control plants. These 
results indicate that the aphids are carriers of the virus, and that spinach- 
blight is caused by a specific virus which can be transferred from plant 
to plant by needle pricks as well as by aphids. 
Station farm. —Blighted plants were collected from the Station field 
and piled on the ground in the edge of the woods near the greenhouse. 
Pots of spinach seedlings from seed from six different sources were placed 
in wire cages so as to have seed lots 1,2, and 3 in one cage and 4, 5, and 
6 in another. Two such series were made, a total of 12 pots in four 
cages. Some of the blighted plants from the above-mentioned pile 
were placed in each cage, care being exercised that the blighted plants 
did not touch the seedlings in the pots. The next day it was observed 
that Macrosiphum solanifolii and Rhopalosiphum persicae had crawled 
from the leaves of the blighted plants onto the leaves of the seedling 
plants; therefore the blighted plants were carefully removed from the 
cages so that they did not touch the seedlings. Six days later seedlings 
in seed series 1 and 5 had the mottled leaves characteristic of blight, 
and 11 days Jater a large percentage of the seedlings in each of the seed 
