July 1, 1925 
Overwintering and Dissemination of Cucurbit Mosaic 
29 
These experiments demonstrate that milkweed plants when once 
infected with mosaic will produce mosaic shoots during succeeding 
seasons. Field observations during 1921 supported this belief, as 
mosaic milkweed plants were found during July, 1921, at all points 
where they occurred in 1920. These observations included the Olin 
plat at Madison, Wis., three fields at Rockland, Wis., and two at 
Marengo, Ill. In all of these fields the mosaic milkweed plants were 
found in the same spots during both 1920 and 1921, while at Madison 
the record also included 1919. In addition to these data, 12 mosaic 
milkweed plants were marked in the plat at Madison during the fall 
of 1920. Observations during June and July, 1921, showed that 
shoots of mosaic milkweed plants had appeared within 6 feet of nine 
of the points marked. In the other three instances no plants were 
seen during the season. 
Trials with Seed from Mosaic Milkweeds 
As already mentioned, mosaic milkweeds rarely produce seed. 
In a few cases, however, seed has been obtained from them, and 
experiments have been conducted to determine whether the mosaic 
disease is carried over winter in the seed as well as in the roots of 
mosaic plants. The seed from mosaic plants was grown in flats of 
sterilized soil in a greenhouse in which the temperature was held at 
approximately 28° C. Seed from healthy plants was grown in other 
flats in the same house as a control. Up to the present, 387 seedlings 
have been grown from the seed of mosaic milkweed plants, but no 
evidence of mosaic has been noted on any of these plants, many of 
which were grown until they had reached a considerable size. These 
results, therefore, indicate that the disease is not carried in the seed 
of mosaic milkweed plants. 
IMPORTANCE OF THE MILKWEED AS A SOURCE OF CUCURBIT INFECTION 
In view of the evidence just given, it is apparent that the milkweed 
is susceptible to cucurbit mosaic, and that the perepnial rootstalks 
of mosaic milkweed plants carry the disease over the winter. As 
with the wild cucumber, however, the importance of the milkweed 
as a source of infection rests on the nature of the carriers which trans¬ 
mit the disease to the cultivated cucurbits, and upon the time of 
appearance, number, and location of the mosaic milkweeds. 
Insect Carriers of Milkweed Mosaic 
aphids 
The cucumber aphis (Aphis gossypii), as shown in this paper, 
is known to be an agent in transmitting mosaic from the milkweed to 
the cucumber. These aphids are commonly found on milkweed 
plants in the vicinity of cucumber fields infested with the insects, 
but are comparatively rare on milkweeds at a distance from culti¬ 
vated cucurbits. Other species of aphids are often found on the 
milkweed, but up to the present no other species has been found 
which will feed on the cucumber. It seems probable, therefore, 
that in most cases the cucumber aphids reach the milkweed from 
infested cucurbits in the vicinity. 
