July i, 1925 Overwintering and Dissemination of Cucurbit Mosaic 
21 
to plants of other families than the Cucurbitaceae these results had 
little bearing on the problem of overwintering. More recent inves¬ 
tigations, however, have shown that a number of plants of families 
outside the cucurbits are susceptible to cucurbit mosaic, and among 
these the milkweed, Asclepias syriaca , is an important agency in the 
overwintering of the disease. 
FIELD OBSERVATIONS 
The occurrence of mosaic on the milkweed was noted in 1916 by 
E. A. Bessey, of the Michigan Agricultural Experiment Station, who 
sent specimen plants to the senior writer. Inoculations were made 
to cucumber plants with this material, but no infection resulted. 
Milkweed plants which appeared to be mosaic were also found 
during 1917 and 1919, and a number of inoculations were made to the 
cucumber; but, prior to 1920 (<5), there was no evidence, as far as 
the writers are aware, that milkweed mosaic was transmissible to 
the cucurbits. The studies with the wild cucumber, however, led 
indirectly to a further interest in the problem of the relation of the 
milkweed to the overwintering of mosaic. 
At Madison, Wis. 
During the summer of 1919, an effort was made to locate the source 
of primary infection in a field known as the Olin plat at Madison, 
Wis., which had been used for the experiments on the overwintering 
of mosaic in the soil. This plat was isolated and at a considerable 
distance from other cucumber fields, but it was noted that mosaic 
appeared there earlier and in more severe form than at any other 
point in the vicinity. 
Several careful inspections failed to show the presence of mosaic 
wild cucumber plants within a mile of this point, although in most 
other mosaic-diseased fields about Madison it was possible to find 
wild cucumber plants sufficiently near to account for the infection. 
The early appearance of the disease on the Olin plat added to the 
peculiar aspect of the problem, and consequently all wild plants in 
the vicinity were examined for evidences of mosaic. It was found 
that the plat itself contained approximately 20 milkweed plants 
which showed marked symptoms of a disease similar to cucurbit 
mosaic. A further investigation of milkweeds in the neighborhood 
failed to show any other mosaic plants, and this fact added to the 
importance of the discovery, for it indicated a possible relation 
between the diseases on the two hosts. Such a possibility was of 
} )articular importance, as the milkweed is perennial and could there- 
ore carry the disease over winter if susceptible. 
The Olin plat was again planted to cucumbers in 1920, and record 
was made of the mosaic milkweed plants which appeared there. Ap¬ 
proximately 20 such plants were found between the rows of cucum¬ 
bers up to July 12, in addition to a considerable number of healthy 
plants. The first infection on the cucumber was noted July 12, and 
the field was thereafter inspected at intervals of three to four days. 
As the disease developed, record was made of the location of each 
mosaic plant and the proximity of mosaic milkweeds. These obser¬ 
vations showed that practically all of the early infection on the cu¬ 
cumber had occurred within 6 to 10 feet of mosaic milkweeds, as 
shown by the accompanying field plan (fig. 1). 
