26 
Journal of Agricultural Research 
Vol. XXXI, No. 1 
from the field, were placed in cages and inoculated by means of aphids 
taken from mosaic cucumber plants. Healthy cucumber aphids 
were also placed on three other healthy milkweed plants as controls. 
The inoculations were made on February 4, and on February 24 all 
the aphids present on the plants were removed by spraying with 
nicotine sulphate. Aphids from healthy cucumber plants were 
transferred to both the inoculated and control milkweeds on March 1, 
and on March 7 some of the insects from each set of milkweeds were 
transferred to healthy cucumber plants under separate cages. The 
results of these inoculations, given in Table XI, show that infection 
occurred on the cucumbers on which aphids from the inoculated milk¬ 
weeds were placed, while the aphids from the controls produced no 
infection. „ 
/ ’ 
Table XI .—Results of cross inoculations of healthy cucumber plants from milk¬ 
weed plants inoculated with cucurbit mosaic by means of aphids 
Milkweed Plants Inoculated in Field, Aug. 13, 1920 
Date of inoculation 
Milkweed 
used as in¬ 
oculum 
Method of inoculation 
Number 
of cu¬ 
cumber 
plants 
inocu¬ 
lated 
Number 
of mosaic 
plants 
- Date ob¬ 
served 
Sept. 1,1920. . 
1-1 
Aphids_ _ 
4 
4 
Sept. 13,1920 
Do. 
* Do.. 
o 23-1 
_* .do.... 
4 
0 
Do... 
1-1 
Crushed leaf tissue_ 
4 
3 
Do. 
nn 
“23-1 
.do__ 
4 
0 
Do. 
Sept. 4, 1920. 
1-1 
_do... 
11 
7 
Sept. 15,1920 
Do. 
‘ Do. 
oi_4 
.do___ 
10 
0 
Do.. 
7-1 
Aphids.... 
4 
3 
Do. 
Do_ 
“1-4 
../..do___ 
4 
0 
Do. 
Sept. 10,1920... 
17-1 
.do... 
4 
4 
Sept. 19, 1920 
Do. 
* Do._ 
“23-2 
.do.—..—... 
4 
0 
Do.. 
17-1 
_do.... 
4 
2 
Do. 
Do.. 
“23-2 
_do____ _ 
4 
0 
Do. 
Sept. 12, 1920_ 
17-1 
_do_____ 
5 
5 
Do. 
Dn ' 
“22-1 
_do... 
5 
0 
Do. 
Do. 
17-2 
.do__ 
5 
5 
Do. 
Do. 
“22-2 
_do. _ 
5 
0 
Do. 
Milkweed Plants Inoculated in Greenhouse, Mar. 20, 1921 
Apr. 11,1921_ 
A-l 
Crushed leaf tissue_ 
8 
3 
Apr. 25, 1921 
Do. 
Do.. 
A-3 
_do.. . _ 
8 
4 
Do_ 
A-4 
_do__ 
8 
5 
Do. 
Do__ 
A-5 
_do_ 
8 
0 
Do. 
Do. 
A-6 
_do_____ 
8 
3 
Do. 
Do . 
“ A-8 
.do___ 
8 
0 
Do. 
Do. 
“ A-9 
_do.. 
8 
0 
Do. 
• Control plant. 
The results of direct inoculation from the cucumber to the milk¬ 
weed have been less uniformly successful, as only 2 definite cases of 
mosaic have been produced out of 15 plants inoculated in the field 
and greenhouse. These inoculations were made by inserting the 
crushed leaf tissue of a mosaic cucumber plant into longitudinal 
incisions at various points in the stems of nealthy milkweeds and 
also by pricking the juices of mosaic cucumber plants into the younger 
leaves. The excessive flow of latex which follows the slightest wound¬ 
ing of the milkweed may account in part for the difficulty experienced 
in infecting by this method. 
