54 
J ournal of Agricultural Research 
Vol. XXXI, No 1 
downward curling of the youngest leaves, and at the end of 12 days 
a definite mottling began to appear. In the course of the next 2 
weeks the mosaic plants developed typical mosaic symptoms and the 
leaves were mottled and deformed as the new growth developed. 
The early symptoms of the disease on the pigweed are less marked 
than with any plants on which the writers have obtained infection, 
and for this reason the incubation period at first appears to be longer 
than it really is. As the experiments have been continued it has 
become evident that the incubation period for this host is approxi¬ 
mately the same as for the cucurbits, varying from 7 to 9 days. 
As shown in Table XXIV, infection has been accomplished on the 
pigweed by both methods of inoculation. The artificial inoculations 
were made in the same manner as those used in inoculating cucumber 
plants from mosaic pigweeds and a fair amount of infection resulted 
from this method. The results of these experiments indicate that the 
pigweed is readily infected with cucurbit mosaic and that such 
infection occurs under natural conditions in the field. The occurrence 
of such natural infection has often been observed in fields where pig¬ 
weeds were growing between rows of cucumbers affected with mosaic. 
Up to the present the only mosaic pigweeds which have been found 
have apparently been infected from the cucumber and there is no 
evidence to indicate that the disease is carried over winter by this 
host. 
Table XXIV .—Cross inoculations from mosaic cucumbers to healthy plants of 
Amaranthus retroflexus 
Date of inocu¬ 
lation 
Method of inoculation 
Location 
Number 
of plants 
inocu¬ 
lated 
i 
Number 
of plants 
mosaic 
Date observed 
Apr. 21,1921 
Aphids from mosaic cucumber plant... 
J Greenhouse . 
1 
1 
May 9,1921 
July 14,1922 
_do_ 
1 _do_ 
4 
4 
July 31,1922 
Do. 
Aphids from healthy cucumber plant 
|.do_. 
4 
0 
Do. 
(control). 
July 19,1922 
Aphids from mosaic cucumber plant.. _ 
'_do_ 
8 
8 
Aug. 1,1922 
Do_ 
Aphids from healthy cucumber plant 
_do_ 
8 
0 
Do. 
(control). 
Aug. 2,1922 
Artificial... . 
'_do_ 
10 
6 
Aug. 18,1922 
Do 
Control _ _ _ 
.do.. 
10 
0 
Do. 
Aug. 10,1922 
Artificial__ 
_do_ 
5 
3 
Aug. 28,1922 
Do.. 
Control 
_do_ 
5 
0 
Do. 
- 
SYMPTOMS OF CUCURBIT MOSAIC ON AMARANTHUS RETROFLEXUS 
Mosaic Amaranthus plants are much dwarfed and usually reach a 
height of only 8 to 10 inches, while healthy plants are often 2 to 3 
feet tall. The' affected plants show a typical mosaic mottling of the 
foliage, the major portion of the leaf becoming a yellowish-green 
with smaller dark-green areas scattered over the surface. The 
petioles of such leaves are usually longer in proportion to the blade 
than those of healthy plants, and this, together with the shortening 
of the internodes, gives the mosaic plant an abnormally spreading 
habit (pi. 3, E). The leaves of mosaic plants are usuaily smaller, 
narrower, and more irregular in outline than those of healthy plants. 
Mosaic plants usually develop only a single stem and do not branch 
as commonly as do healthy pigweeds. Seed is produced by mosaic 
plants, but only in small amounts. 
