July i, 1918 
True Nature of Spinach-Blight 
37 
A series of inoculations (see Table IX) were made, supplementing the 
transfers of the live insects. Aphids from the same sources as those used 
in the transfers were crushed and the juice thus obtained was inoculated 
into the tissues of the healthy plants by means of needle pricks. Fifty 
healthy plants were inoculated with the juice of Macrosiphum solanifolii 
(Norfolk, Va., strain) which had previously been feeding on lettuce. 
Four plants became infected, and symptoms of blight developed in an 
average time of 29.2 days. Fifty plants were inoculated with the juice 
of M. solanifolii (Norfolk, Va., strain) which had previously been feed¬ 
ing on spinach. Eight plants developed symptoms of blight in an aver¬ 
age time of 31.6 days. Fifty plants were inoculated with the juice of R . 
persicae (Norfolk strain) which had previously been feeding on lettuce. 
One plant became infected. The first positive symptoms of the disease 
appeared in 36 days. Fifty plants were inoculated with the juice of 
R . persicae (Norfolk strain) which had previously been feeding on spinach. 
Four plants became infected in 31.9 days. In a similar nianner healthy 
spinach was inoculated with the juice of M. solanifolii (Auburn, Ala., 
strain) from lettuce and healthy spinach. Healthy spinach was inocu¬ 
lated with the juice of R. persicae (Baton Rouge, La., strain) from pepper, 
healthy spinach, and lettuce. The juice obtained from crushed R. per - 
sicae (Fort Collins, Colo., strain) which had been feeding on peach and 
healthy spinach was inoculated into healthy spinach seedlings. All of 
these inoculations gave negative results, the plants remaining healthy 
until the experiment was closed, two months after the inoculations had 
been made. 
TablB IX .—Results of inoculations with the juice of crushed , supposedly non-virus¬ 
bearing aphids 
Species used 
Source of insect. 
Previous 
food plants 
of insect. 
Number 
of plants 
inocu¬ 
lated 
with the 
juice of 
crushed, 
suppos¬ 
edly 
non- 
virus¬ 
bearing 
aphids. 
Number of 
plants 
infected. 
Aver¬ 
age 
length 
of incu¬ 
bation 
period. 
Macrosiphum solanifolii. .. . 
Do. 
Norfolk, Va. 
.do. 
Lettuce.. 
Spinach . 
Lettuce.. 
Spinach . 
Lettuce.. 
Spinach . 
Pepper... 
Spinach . 
Lettuce.. 
Peach.... 
Spinach . 
50 
50 
50 
50 
2 5 
2 5 
2 5 
2 5 
2 5 
10 
2 5 
. 4 . 
. 8 
Days . 
29. 2 
3 1 * 6 
36 
3 1 * 9 
Rhopalosiphum persicae. . . . 
.do. 
T 
Do. 
.do. 
M. solanifolii . 
Do. 
Auburn, Ala. .. 
All healthy. 
Ho 
R. persicae . 
Baton Rouge, 
La. 
.do 
Do. 
Ho 
Do. 
. . . .do 
Do... 
Fort Collins, 
Colo. 
.. .do 
Do... 
Ho 
