22 
Journal of Agricultural Research 
Vol. XIV, No. x 
The results obtained in these series indicate the improbability of let¬ 
tuce or eggplant serving as alternate hosts of the virus. The possibility 
of experimental error or outside infection was also rendered unlikely 
through the various duplications of the work. The fact remains that 
aphids which had never come in contact with spinach produced a small 
percentage of infections when placed on healthy spinach plants; also, the 
juice of aphids similarly treated produced the disease in a few cases when 
inoculated into healthy plants. 
NATURAL, INFECTION OF SPINACH PLANTS 
NATURAL INFECTION OF GREENHOUSE SEEDLINGS BY VIRUS-BEARING 
APHIDS 
Blighted spinach plants were collected, transplanted to a bench in the 
greenhouse, and covered with a large glass cage. Some American-grown 
spinach seed which had been soaked for a few minutes in i to ioo for¬ 
maldehyde was planted in this cage. Ten days after transplanting the 
blighted plants to the greenhouse cage it was observed that they were 
dying and that the aphids from these plants had crawled to the seedling 
plants which had come up about six days after planting the seed. Only 
the cotyledon leaves had developed on the seedling plants at that time. 
The aphids in this cage were killed by fumigation a short time thereafter 
and the transplanted blighted plants died. About 30 days after the 
seedlings had come up it was observed that some of them had developed 
characteristic symptoms of blight, and within the next 10 days the 
majority of the plants had developed striking symptoms. This included 
some 25 plants in all. About 40 days after the seedlings had come up, the 
aphids in this case having been killed by fumigation, a pot of 12 seedling 
plants was set in this cage among the blighted plants. Thirty-five days 
later none of the seedlings in this pot had developed any symptoms of 
blight, although they were surrounded by blighted plants. This indi¬ 
cates that blight is not transferred except by aphids or some mechanical 
means. After making this observation, individuals of Rhopalosiphum 
persicae known to be free from infection were transferred to this cage. 
Twenty-nine days later the majority of the plants in the pot of healthy 
seedlings previously transferred to this cage had developed characteristic 
symptoms of blight, thus indicating that the aphids had traveled and 
carried infection from the blighted to the healthy plants in the pot. 
A number of R. persicae from blighted plants in the above cage were 
transferred to large plants in a field cage. Similar plants in the large 
cage were used as controls. Thirty-one days after they had been inocu¬ 
lated all of the plants had developed characteristic symptoms of blight, 
while the control plants remained healthy. These results substantiate 
those of previous experiments to the effect that spinach-blight is a specific 
disease which may be produced either in the field or in the greenhouse, 
