July i, 1918 
True Nature of Spinach-Blight 
49 
alive, and it had only a small whorl of mottled leaves at the center, the 
older leaves having degenerated, similar to those of blighted plants in 
the field. On November 15 one mottled leaf was removed from this 
remaining large plant, and with it a pot of several spinach seedlings 
growing in a greenhouse cage was inoculated by mashing the diseased 
tissues into the leaves of the seedling. Seedlings in a similar pot were 
mashed with a flamed needle to serve as controls. On November 27 
some of the seedling plants in the pot inoculated on November 15 had 
developed the typical mottled leaves. 
On November 15 two mottled spinach seedlings from the seed planted 
in the field cage on October 6 were removed from this cage, and with 
them one pot of healthy spinach seedlings growing in a greenhouse cage 
was inoculated by mashing the diseased tissues into the potted seedlings. 
A similar pot of seedlings was mashed with a flamed needle and served as 
a control. On November 27 mottled leaves had developed on the inoc¬ 
ulated seedlings, but the control plants appeared healthy. 
On August 9, when the aphids were transferred from the field cage in 
which they had summered to spinach seedlings in another field cage, 
some leaves from the potato and pepper plants on which they had sum¬ 
mered were removed from the field cage, and potted spinach plants in a 
cage in the greenhouse were inoculated with them by mashing their 
tissues into the leaves of the spinach seedlings. These spinach seedlings 
were under observation until November 27, but no signs of mottled 
leaves developed, and the plants grew to a large size and had the dark- 
green color characteristic of healthy spinach plants. These results indi¬ 
cate that the pepper and potato plants on which the aphids had fed during 
the summer did not act as alternate hosts for the spinach-blight virus. 
The record of the direct line of aphids kept on pepper, eggplant, and 
potato plants in a field cage during the summer and then transferred to 
spinach at about the time early spinach is planted in the field in the fall 
indicated that a direct line of aphids from a known virus-bearing parent 
may carry the infectious entity of spinach-blight over the summer even 
though they do not feed on spinach during that time. This record 
substantiates the other evidence which has been accumulated and points 
toward the probability that aphids are the important factor in the sum¬ 
mering of the spinach-blight virus. 
RELATION OF LEFT-OVER SPINACH PLANTS TO THE SUMMERING OF SPINACH- 
BLIGHT 
It often happens that, when spinach fields are plowed after the late 
spring crop has been harvested, plants may be left growing along the edges 
of the field. On July 8, 1917, several diseased plants were found which 
had escaped the plow earlier in the season. Bither species of aphids 
whose life averages between 30 and 40 days could pass the time elapsing 
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