22 
Journal of Agricultural Research 
Vol. XXXI, No. 1 
Aside from these plants, there was practically no mosaic infection 
on the cucumbers in this plat until about July 25. The cucumber 
aphis {Aphis gossypii) was present in considerable numbers from 
July 1 to the end of the season, and as a result 75 per cent of the 
cucumber plants became mosaic diseased between August 1 and 
August 15. The aphids were present on the mosaic milkweeds before 
the disease developed on the cucumber plants, and their presence on 
the milkweed supported the theory that this plant might be a source 
of primary infection to the cucumber, as the aphids were known to be 
carriers of the disease. If this were the case, the cucumbers directly 
adjacent to the mosaic milkweeds would probably be the first infected, 
for aphids ordinarily do not travel very far. As a result of these ob¬ 
servations, it seemed probable that the milkweed might be of consid¬ 
erable importance in relation to cucurbit mosaic. 
At Rockland, Wis. 
Soon after the above observations were made, further evidence 
was obtained at Rock¬ 
land, Wis., which even¬ 
tually established the 
milkweed as a source 
of mosaic infection for 
the cultivated cucurbits. 
During1920, experiments 
in regard to the possible 
control of cucurbit mo¬ 
saic through the removal 
of wild cucumber plants 
were conducted at Rock¬ 
land and all mosaic Mi- 
crampelis plants which 
could be found in the 
vicinity were removed 
during June and early 
July. Inspections were 
made about every two 
weeks and no mosaic was 
found on cucumbers in 
occurrence of first'mosaic infection on cucumber plants directly the 
adjacent to mosaic milkweeds. July 12 to 19,1920 - 
5. 
fields in the area from which wild cucumbers had supposedly been 
removed was found to be 90 per cent mosaic diseased. As only two 
other fields in the vicinity showed any trace of mosaic and as the 
infection was comparatively slight in both cases, the source of infec¬ 
tion in the badly diseased field furnished a peculiar problem. A brief 
investigation, however, showed that nearly 100 mosaic milkweed 
plants were growing between the rows of cucumbers and that both the 
cucumbers and milkweeds were heavily infested with the cucumber 
aphis. Further inspection revealed the presence of mosaic milkweed 
plants in another of the less severely infected fields, and in this case 
also aphids were found on both hosts. The evidence at Rockland 
and Madison was so striking that cross-inoculation experiments were 
immediately begun in a further attempt to determine the possible 
identity of the mosaic diseases occurring on the two hosts. 
vicinity until August 
On this date one of the 
— ROW 
X MOSAIC CUCUMBER PLANT 
• MOSAIC MILKWEED 
Fig. 1.—Plan of exnerimental nlat at Madison. Wis.. showiner 
