50 
Journal of Agricultural Research 
Vol. XIV, No. I 
between the ist of July and the time the early fall spinach is above the 
ground by four last-born generations; hence, in this case one of the 
factors hindering spring-to-fall transmission of the disease by aphids 
would be eliminated. 
At the edge of a field on a farm near the Station one spinach plant 
left from the spring crop was observed on June 4, 1917. This plant 
had been left because it was in line with a cucumber row. It did not 
appear to have typical symptoms of blight, although some of the leaves 
were yellow. A number of Macrosiphum solanifolii were present on this 
plant. One leaf-bearing aphid was removed and brought to the green¬ 
house, where the aphids were placed on a pot of spinach seedlings. 
Another pot of seedlings was inoculated by mashing the tissues from the 
field plant into the leaves of the healthy seedlings. Similar pots of 
plants were pricked with a flamed needle to serve as controls. Fourteen 
days later, in the pot to which the aphids had been transferred, there were 
several plants with the mottled leaves characteristic of blight. Twenty- 
six days after inoculation three plants having characteristic symptoms 
of blight were observed in the pot of seedlings which had been inoculated 
with the leaf of the field plant from which the aphids were removed. 
These results indicate that the few plants which are allowed to remain 
in the fields after the regular crop has been harvested are the collecting 
places for numerous aphids, thus making the possibilities great for such 
plants becoming diseased with spinach-blight, and serving to carry the 
disease well into the summer after the regular crop has been harvested. 
It is known that this field plant grew for some time after aphids had been 
transferred from it to the greenhouse. A rank growth of weeds eventually 
surrounded this plant, so that it was impossible to determine how long 
it remained alive and served as a source of infection. The evidence 
which we have points toward the probability that aphids are instrumental 
in carrying the disease over the summer by their power to transmit the 
casual factor from parent to offspring for several generations. Probably 
this is not the only means by which spinach-blight may pass the summer 
period. As more is learned concerning the relationship between blight, 
insects, and plants other than spinach, doubtless other means may be 
discovered. 
ABILITY OF OTHER INSECTS INFESTING SPINACH TO TRANSMIT 
SPINACH-BLIGHT 
With the exception of the bean aphis, none of the species included are 
generally active during the winter months, and for these reasons are not 
liable to become important, from their agency as transmitters of blight 
virus. Experiments were performed in which most of the insects in¬ 
festing spinach in this region were transferred from diseased to healthy 
plants. The insects remained on the plants in each case for 48 hours. 
