56 BULLETIN ST9. V. 8. DEPABT^IEXT OE AGPJCrXTTBE. 
are of rather doubtful value as evidence of tne occurrence of the 
disease from the seed. While these data seem overwhelminglv 
negative at first glance, the single case of mosaic which developed 
from the seed of mosaic vines was of such a character that it is 
difficult to explain its appearance on any basis other than that of 
seed transmission. It is doubtful whether cucumber mosaic is seed 
borne to any considerable extent, but it seems possible that it may 
occur in rare cases, and the results so far obtained have left the prob- 
lem still open, warranting further investigation. In general, the 
disease appears every year hi most infested districts, and in a 
maimer that would preclude any belief in seed transmission as the 
sole cause of its outbreak. In districts where the disease had not 
appeared, however, a single case of seed transmission hi several 
thousand plants would be sufficient to introduce the disease, and the 
many agents of dissemination present would insure its rapid spread 
to other plants and fields. 
INSECTS IX RELATION TO OVERWINTERING. 
The amount of cucumber mosaic present each year hi various 
localities has frequently been in direct relation to the number of 
cucumber insects in the fields. This would be expected hi view of 
then importance as agents of dissemination. It has been found, 
also, that the first appearance of the disease in many localities seems 
closely related to the number of insects present, as far as the amount 
of the early infection is concerned. During 1916 and 1917 there 
was an unusually small number of cucumber insects in southwestern 
Michigan, and the disease appeared hi a much less severe form than 
in previous seasons. During the same period, cucumber insects at 
Madison. "Wis., and hi adjacent localities were present in unusually 
large numbers in June and July, particularly the Diabrotica species. 
The disease developed there with great severity both years, several 
fields in 1917 having 15 to 25 per cent of the plants affected within 
five days from the time the first case was noted. These observations 
led to the belief that insects might bear some part in the overwintering 
of mosaic. 
THE RELATION OF APHIDS TO OVERWINTERING. 
During 1915 and 1916 an attempt was made to overwinter aphids 
taken from mosaic vines, but no insects appeared hi the spring and, 
as little is known of the method by which this insect passes the whiter, 
the work was finally abandoned. As the cucumber aphis (Aphis 
gossypii) has always appeared rather late hi the season a ad not until 
-dine time after the disease developed, it is probable that this insect 
is not a factor hi the first appearance of the disease. This is further 
indicated by the fact that aphids are not present every year in locali- 
ties where tiie disease appears each season. 
