52 BULLETIN 879, IT. S. DEPARTMENT OF AGEICULTUEE. 
normal in size and appearance at maturity, a great number are 
included with the seed crop each year and there is no doubt that 
much of the seed stock furnished to growers contains many seeds 
from mosaic vines. 
During the last four years a number of cases of infection have been 
observed which gave some support to the theory of transmission of 
mosaic through the seed. At Hamilton, Mich., in 1914, careful field 
observations had been made during the first 10 days of July, and but 
one field was found in which mosaic was present. On July 12, how- 
ever, at a distance of 4 miles from the town, a small patch of cucumbers 
was found in which 25 per cent of the plants were diseased. The 
plants were growing on land cleared the year previous and were 
surrounded by a belt of woods. No other cucumbers were within 2 
miles, and the only mosaic plants found up to that time were 4 miles 
away. The plants showed no insect injury, and it was difficult to 
explain the origin of such early infection except by seed transmission. 
Another striking case occurred at Big Rapids, Mich., in 1915. 
This locality was practically free from mosaic, and none was found 
until July 24. On this date one mosaic plant was found in the center 
of a 2-acre experimental plat of cucumbers. The land had never 
grown 'cucumbers before, and the few additional fields in the vicinity 
were free from the disease. The plant found was immediately covered 
with a cheesecloth cage, to prevent the spread of infection, and no 
further cases appeared during the summer with the exception of 
plants inoculated under cages. 
Several other instances of infection occurring early in the season in 
isolated fields have been noted, and a few si mi lar cases have appeared 
in the greenhouse, where the mosaic suddenly developed during the 
winter in houses that had previously been free from it and were so 
isolated that outside infection seemed unlikely. 
McClintock (22) reported observations made at the Virginia Truck 
Experiment Station at Norfolk which he believes may indicate the 
transmission of cucumber mosaic by the seed. Plants from the 
greenhouse were transplanted to coldframes in the field, in some cases 
on sterilized soil. Considerable mosaic was later found on these 
plants, and no evidence of insects or insect injury was noted. 
All field observations of the type mentioned are open to objection, 
however, in so far as they are taken as definite evidence of the trans- 
mission of the disease by the seed. So many sources of infection 
exist and their detection is often so difficult that infection may occur 
in isolated localities from sources that are easily overlooked. In- 
sects, such as striped beetles, may travel considerable distances, 
especially in high winds, and might infect a few plants and disappear 
soon after. Mosaic plants of the wild cucumber ( Micrampelis lobatd) 
may also be present, being often overlooked because of their loca- 
