34 
Journal of Agricultural Research 
Vol. XXXI, No. 1 
When aphids were used as a means of inoculation they were 
colonized on healthy cucumber plants under cages in the greenhouse 
or field. Healthy aphids from this stock were later transferred to 
the plant to be inoculated. The insects were ordinarily transferred 
by means of a earners hair brush, and the number placed on each 
plant varied from 10 to 60. Ordinarily 10 to 15 aphids are found 
sufficient to insure infection, but in the earlier experiments with the 
pokeweed it was found that only a small percentage of the aphids 
remained on the plants after their transfer and the number used was 
therefore increased. 
INFECTIOUS NATURE OF POKEWEED MOSAIC 
As already shown by Allard (2), pokeweed mosaic is readily trans¬ 
mitted to healthy plants of this species by artificial inoculation. In 
order to be certain that the plants supposedly infected by n^eans of the 
cucumber aphis were actually mosaic diseased, a number of inocula¬ 
tions were made from these plants to healthy pokeweeds, both by 
means of insects and by artificial methods. The results given in 
Table XIII show that the disease is readily transmissible to the poke- 
weed by either method of inoculation. The incubation period of the 
disease of the pokeweed, as in the case of that of the cucumber, varies 
to some extent with the rapidity of growth of the infected plant. 
The average incubation period appears to be from 5 to 10 days, and is 
therefore approximately identical with that of cucurbit mosaic. 
Table XIII .—Results of inoculations of healthy pokeweeds from pokeweeds infected 
with cucurbit mosaic 
Date of 
inoculation 
Source of inoculum 
Number 
of plants 
inocu¬ 
lated 
Number 
of plants 
mosaic 
Date 
observed 
1922 
Mar. 15_ 
Aphid Inoculation « 
Aphids from mosaic pokeweed___ 
9 
6 
1922 
Mar. 30 
Mar. 22. 
_do___ _ 
4 
2 
Apr. 7 
Apr. 10 
Mar. 31 
Mar. 31_ 
_do___ 
1 
1 
Mar. 6__ 
Artificial Inoculation 
Crushed leaf tissue of mosaic pokeweed_ __ _ _ 
6 
2 
Mar. 22. 
do ____ 
8 
8 
Apr. 6 
Do._. 
Control___ _ 
8 
0 
Do. 
Mar. 23_ 
Crushed leaf tissue of mosaic pokeweed__ 
8 
2 
Apr. 11 
Do. 
Do.- 
Control_ _ _ 
8 
0 
Mar. 25. 
Crushed leaf tissue of mosaic pokeweed_ 
3 
1 
Do. 
Do_ 
Control_ _ 
3 
0 
Do. 
Apr. 13. 
Crushed leaf tissue of mosaic pokeweed__ 
24 
20 
Apr. 26 
Do. 
Do. 
Control_ ___ 
24 
0 
Apr. 24_ 
Crushed leaf tissue of mosaic pokeweed.... 
12 
12 
May 18 
i Do. 
! 
Do. 
Control_____ __ __ 
12 
0 
1 
a Because of the fact that aphids had failed to colonize on the healthy plants intended for use as controls 
during these experiments, a number of healthy plants in the greenhouse were used as controls. None of 
the plants of this healthy stock developed mosaic. 
SYMPTOMS OF MOSAIC ON THE POKEWEED 
The symptoms of pokeweed mosaic are very similar to those of 
the mosaic diseases affecting the cucumber and tobacco. The disease 
first appears on the young leaves as a mottling of light greenish yellow 
in which the light areas are of small size. This mottling is accompa¬ 
nied by a downward curling of the midrib of the leaf, similar to 
» 
