THE MOSAIC DISEASE OF CUCURBITS. 47 
rather rare. Field observations, moreover, give little support to the 
theory that bees are a factor in mosaic dissemination, since in many 
cases where few other insects were present the spread of the disease 
would in all probability still have been rapid if the bee were a carrier, 
whereas in such cases the increase of infection was relatively slow. 
POLLEN AS A CARRIER OF INFECTION. 
The work with bees has also brought up the question of possible 
infection through the fertilization of flowers of healthy plants with 
pollen from the blossoms of mosaic plants. This has been tested by 
artificial fertilization of healthy cucumber flowers with pollen from 
mosaic vines, the operation being performed with a camel's-hair 
brush to avoid wounding the flower parts. Although many fruits 
were thus produced, no mosaic infection has ever been found. In 
these experiments care was taken to protect the blossoms from outside 
pollen and to make certain that the fruits set were pollinated only 
with pollen from mosaic plants. 
METHOD OF OVERWINTERING. 
FIELD OBSERVATIONS. 
Since the factors concerned in the field transmission of the disease 
are sufficiently well established to account in large measure for its 
rapid dissemination, the problem of its overwintering and reappear- 
ance each year is perhaps most important, aside from the actual 
cause, in relation to possible methods of control. 
As before stated, the origin of the disease seems unrelated to soil or 
climatic conditions., and its appearance is dependent on some specific 
infection. For the past four years it has appeared in Michigan, Indiana, 
and Wisconsin at approximately the same time, the first reports of 
its occurrence each year having been somewhere between July 7 and 
July 20, at a time when the plants were from 5 to 6 weeks old and 
had from 8 to 10 leaves. Infection of very young plants is rare 
and has usually appeared in cases where the seed was planted very 
late in the season, at a time when infection was already present on 
older plants in the same field. 
The regularity in the appearance of the disease extends to most 
localities in the States mentioned, and a survey of the cucumber- 
growing districts of Michigan or Wisconsin about the middle of July 
usually shows the disease developing almost simultaneously in most 
localities where it was severe the year previous. In many cases the 
first infections are found on a few plants scattered through the field, 
or perhaps on plants in a single center, including six to eight vines 
within a short distance of one another, and from these it spreads 
gradually to neighboring plants. This manner of appearance and 
