32 
Journal of Agricultural Research 
Vol. XXXI, No. 1 
grown, it seems probable that the milkweed in most cases is first 
infected from the cucumber. This infection probably occurs chiefly 
through the agency of aphids and the mosaic persists in the milk¬ 
weeds from year to year and thus furnishes a source of primary in¬ 
fection to nearby cucurbits. 
COMPARATIVE IMPORTANCE OF THE MILKWEED AND WILD CUCUMBER IN OVER¬ 
WINTERING CUCURBIT MOSAIC 
When the milkweed was first discovered to be a factor in over¬ 
wintering cucurbit mosaic, it was thought that it was probably of 
minor importance in comparison with the wild cucumber. Further 
investigations, however, have indicated that mosaic milkweeds are a 
serious menace to the cucurbits, and, as far as opportunity for infec¬ 
tion is concerned, they are often of more importance than the wild 
cucumber. This belief is based on field observations made in the 
same localities for three seasons and is further substantiated by the 
results of experimental studies. 
Mosaic wild cucumbers in the majority of cases occur at distances 
of from 100 to 500 yards or more from cucumber fields, except in the 
vicinity of towns, where they occasionally are very near the fields 
and are very numerous. In the case of this host, the Diabrotica 
beetles appear to be the chief means of disseminating the disease, as 
aphids are not commonly found on Micrampelis plants and do not 
cover as great distances as the beetles. It has also been found that 
only a relatively small percentage of the beetles which feed on mosaic 
wild cucumber plants are likely to transmit the disease to cultivated 
cucurbits. The field experiments previously described have also 
shown that at distances of 100 to 500 yards the infection of cucurbits 
from mosaic Micrampelis plants is of irregular occurrence. The 
whole question of infection from the wild cucumber depends on the 
factor of the transmission of the mosaic disease by the Diabrotica 
beetles, and the probability of the transmission of the disease from 
this host is apparently less than in the case of the milkweed. 
The number of mosaic milkweed plants appears to be small when 
compared to the number of wild cucumber plants which have been 
found in the same localities, but in most cases the milkweeds occur 
either within or near the cucumber fields. Aphids are probably the 
most important means of transmitting the disease from the milkweed 
to the cucumber, and these insects will readily travel the distances 
which usually separate the mosaic milkweed plants from the cucum¬ 
bers. Moreover, the aphids are practically certain to produce infec¬ 
tion if transferred to healthy plants, whil e the Diabrotica beetles appear 
to transmit the disease only in a certain percentage of cases after feed¬ 
ing on mosaic plants. Although the situation varies with the locality, 
it is probable that the few mosaic milkweeds which do oc/cur near the 
cultivated cucurbits are of more potential importance than a com¬ 
paratively larger number of mosaic Micrampelis plants which are 
scattered over a wide area. 
OVERWINTERING OF CUCURBIT MOSAIC ON THE POKEWEED 
The presence of a mosaic disease on another perennial, the poke- 
weed (.Phytolacca decandra ), has been known for some time, but until 
recently there was no evidence that it was transmissible to plants of , 
other families. Woods ( 19 ), in 1902, reported the occurrence of a 
