20 
Journal of Agricultural Research 
Vol. XXXI, No. i 
of 1919 brought out the fact there were hundreds of mosaic wild 
cucumber plants in both towns and along the streams in the neigh¬ 
borhood. The number of mosaic centers and the total number of 
such plants found at both Ripon and Princeton was far in excess of 
that at most other points visited. 
As considerable data were available on the previous losses from 
mosaic at most points visited, it was possible by this means to deter¬ 
mine to some extent the probable relation of Micrampelis to infec¬ 
tion in the field. In localities such as Ripon, Princeton, Madison, 
and Sparta in Wisconsin, and Harvard and Marengo in Illinois, 
where mosaic has long been a serious problem, there were consider¬ 
able numbers of mosaic wild cucumber plants. In most of the other 
sections where there were fewer mosaic wild cucumbers, the disease 
has apparently been severe only in certain seasons, although some 
infection occurs each year. 
The probable importance of the wild cucumber in overwintering 
mosaic was also emphasized by the fact long noted that the mosaic 
disease is more severe on cultivated cucumbers in the immediate 
vicinity of towns and villages than in outlying districts. This is 
probably due in part to the proximity of the fields to one another and 
the consequent ease of dissemination of the disease and in part to 
the fact that mosaic wild cucumbers are much more common about 
towns than in the country by reason of the greater use of the Micram¬ 
pelis vine as an ornamental in and near the towns. It was also evident 
that mosaic on the cucumber was much more common in districts 
where there were numerous small streams and low places, which are 
the natural habitat of Micrampelis lobata. 
Reports from other sections indicate that the wild host is common 
in all of the Central and Eastern States. Where surveys have been 
made in those States in sections in which the disease occurs, the 
presence of mosaic wild cucumbers has usually been established. 
The writers therefore consider that they are justified in regarding 
Micrampelis lobata as an important source of mosaic infection in 
most regions where cucurbits are grown on a commercial scale. 
Recent investigations have shown that the milkweed (Asclepias 
syriaca) and the pokeweed (Phytolacca decandra) are also concerned 
in the overwintering of cucurbit mosaic and that they are frequently 
a source of primary infection to the cucurbits. Because of these 
other agencies by which the disease is carried over winter, the 
writers have not been able to definitely determine the comparative 
importance of a single host in this group, because their actual impor¬ 
tance varies with the locality. It is evident, nevertheless, that the 
wild cucumber plays an important part in overwintering cucurbit 
mosaic. 
MILKWEED AS AN AGENCY IN OVERWINTERING CUCURBIT 
MOSAIC 
The existence of mosaic diseases on certain wild plants has been 
known for some time, but until 1920 there was no evidence that 
such diseases could be transmitted to the cucurbits. Jagger (14) 
had successfully transmitted cucumber mosaic to single species of the 
Compositae and Lobeliaceae, and one of the writers of this paper 
(Doolittle) had also brought about infection on Martynia louisiana 
Mill. (8 ), but aside from indicating that the disease was transmissible 
