Journal of Agricultural Research 
Vol. XIV, No. t 
I 4 
These results indicate that the aphids which had fed on blighted 
plants carried the virus to healthy field plants. That the aphids were 
only carriers of the virus and not the true cause of the disease is shown 
by the fact that the virus from the plants artificially infected by the 
aphids produced typical symptoms of the blight when transferred by 
needle pricks to healthy plants in the greenhouse. 
DIRECT VIRUS INOCULATIONS FROM FIELD TO GREENHOUSE AND BACK TO 
FIELD 
Aphids were removed from blighted plants and placed on three pots 
of spinach seedlings. Subsequently the blighted plants were mashed 
in a mortar and the juice pressed out through a cloth. Some of this 
juice was pricked into seedling plants which were then placed under a 
globe in the greenhouse to keep them under more humid conditions. 
Twenty-one days after inoculation two of the plants had developed 
characteristic symptoms of the blight. A similar pot of plants, pricked 
with a flamed needle, covered with another globe, and used as a control, 
remained healthy. With some of the extracted juice, three plants in 
separate pots were inoculated by pricking the virus into the leaves. 
A similar pot of plants was pricked with a flamed needle to serve as a 
control. Eleven days after inoculation symptoms of spinach blight be¬ 
gan to develop in three plants. Twenty-one days after inoculation, two 
of the plants were in advanced stages of blight, while the third was. con¬ 
siderably stunted, but not as mottled as the two others. Eighty-six 
days after inoculation four large plants in a field cage were inoculated 
by mashing into them a leaf from one of the above blighted plants. 
Similar plants in the same cage were pricked with a flamed needle and 
served as controls. Eighteen days after inoculation three of the four 
plants had developed typical symptoms of blight, while the control 
plants appeared healthy. 
DIRECT INOCULATIONS BY APHIDS PROVED BY VIRUS INOCULATIONS 
Individuals of Rhopalosiphum persicae and Macrosiphum solanifolii 
were shaken from blighted plants and placed in a large pot containing 
over ioo spinach seedlings. Twelve days later distinct mottling of some 
of the spinach leaves was observed. Sixteen days after inoculation 
numerous plants had decidedly mottled leaves. Ten days later a large 
percentage of the ioo plants in this pot had developed typical symptoms 
of blight. 
Twenty-three days after inoculation one leaf was removed from each 
of three blighted plants in the above pot, and with these mottled leaves 
seedlings in two pots were inoculated by pricking and mashing the 
blighted tissues into them. A third pot of six plants was inoculated by 
pricking juice from one of the blighted leaves into the seedlings. A 
