THE MOSAIC DISEASE OE CUCURBITS. 51 
The results of these experiments furnish very definite proof that 
the soil plays little, if any, part in the overwintering of cucumber 
mosaic. The fact that the virus has not been found in the tissues 
of old and decayed vines, coupled with the fact that vines protected 
from insects can be kept free from mosaic year after year on soils 
where the disease has been present for several consecutive seasons, 
seems to exclude the soil from consideration as a means of over- 
wintering. 
SEED AS A MEANS OF OVERWINTERING. 
The problem of the transmission of mosaic diseases through the 
seed from infected plants has received much attention from various 
writers in the case of tobacco and tomato. No definite evidence of 
seed transmission in the case of tobacco has ever been obtained, 
although Allard (3) showed the presence of the virus in the flower 
parts, capsules, and mature seed. In the case of tomato mosaic, 
Miss Westerdijk (30) reported a possible example of the transmission 
of the infection by seed. Reddick and Stewart (24) have also stated 
that bean mosaic is seed borne. The question of seed transmission 
of certain mosaic diseases is therefore still an open one. 
FIELD OBSERVATIONS. 
Certain field observations on cucumber mosaic, together with the 
fact that the disease is prevalent in seed-growing districts, have 
made it of great importance to determine definitely whether the 
disease may be carried over on the seed each year. 
As in the case of tobacco mosaic, the fruits of mosaic cucumber 
plants contain the infective principle, and their juices will produce 
infection. As far as can be determined, these juices remain in- 
fectious until the seeds are nearly mature, but the presence of the 
virus in the immature seed or in the tissues surrounding it can 
hardly be definitely proved, since the thick flesh surrounding the 
seeds makes it difficult to remove certain portions of the fruit, including 
traces of the juice from other cells. As stated on page 38, inoculations 
made from mature seed have never shown the presence of the virus, 
but it is possible that the seed may contain the virus in rare cases 
and perhaps afford an opportunity for ovenvintering the disease in 
this way. 
The opportunity for seed infection is present, however, if such 
infection be possible, since the disease is prevalent in many of the 
seed-growing districts. Much of the cucumber seed, especially of 
pickling cucumbers, is grown in the vicinity of Muscatine, Iowa, 
Rocky Ford, Colo., and to some extent in Michigan and Ohio. The 
mosaic disease has been found to occur very commonly in these 
districts, and in handling the crop little or no effort is made to cull 
out fruits from mosaic plants. Since many of these fruits are nearly 
