Jtdy i. 191S 
Trpe Nature of Spinach-Blight 
33 
shorter than when they remained on the plants for either 2 or 14 hours. 
There was apparently no greater number of infections obtained in the 
24-hour period than in either of the others. These data prove that 
aphids have the ability to transmit spinach-blight to several plants after 
leaving a diseased host. In this manner alate forms flying from one 
healthy plant to another after leaving the blighted spinach might infect 
a large number of plants within a comparatively short time, and will 
perhaps explain the sudden and widespread appearance of blight which 
usually occurs after an outbreak of aphids, when many alate individuals 
are produced. 
Table VII. — Ability of aphids to carry infections to more than one healthy plant 
Plant No. 
Length of 
time 
aphids 
remained 
cm plants. 
Number of 
plants. 
Number of 
plants 
infected. 
Average 
length of 
incubation 
period. 
Number of 
insects 
per plant. 
Number of 
plants 
remaining 
healthy. 
Hours. 
Days. 
I. 
24 
4 
4 
15 
2 
I 
ft.. 
24 
4 
3 
17 
2 
I 
3 . 
24 
4 
2 
25 
2 
2 
4 . 
24 
4 
I 
34 
2 
3 
s. 
24 
4 
2 
30 
2 
2 
14 
3 
3 
19 
2 
0 
ft. 
14 
4 
ft 
21 
2 
2 
3 . 
14 
3 
I 
28 
2 
3 
4 . 
14 
4 
0 
0 
2 
4 
5 . 
14 
3 
I 
3 i 
2 
2 
1. 
2 
4 
4 
22 
2 
0 
2 
4 
3 
28 
2 
1 
3 *. .. 
2 
4 
2 
3 1 
2 
2 
4 -. 
2 
4 
1 
30 
2 
1 
s. 
2 
4 
1 
34 
2 
3 
INOCULATIONS WITH THE JUICE OBTAINED BY CRUSHING APHIDS COL¬ 
LECTED ON BLIGHTED SPINACH 
As a check on the data collected in other experiments—namely, that 
the juice of crushed aphids from blighted plants is virulent—the follow¬ 
ing series was started. Several healthy plants were inoculated with the 
virus by means of needle pricks. When the plants had developed 
typical symptoms of blight, a large number of Macrosiphum solanifoln 
and Rhopalosiphum persicae were placed upon them and allowed to feed 
for a period of 20 days. A sufficient number of adults were collected 
from these plants and crushed, about 1 c. c. of juice being thus obtained. 
A series of healthy plants 28 days old was inoculated with this juice. Of 
42 plants inoculated with juice of crushed M. solanifolii, 27 became 
infected, positive symptoms appearing in an average time of 23.1 days. 
Thirty-eight plants were inoculated with the juice of crushed R . persicae, 
57664°—18 - 3 
