THE MOSAIC DISEASE OF CUCURBITS. 55 
any plat during the season, but two plants of Hybrid Casaba melon 
in another plat did later develop typical mosaic symptoms. These 
plants were pulled as soon as found, and no other cases occurred. 
The conditions at Big Rapids during 1917 were unusually favorable 
for a test of this kind, since the district was practically free from 
mosaic, and insects were not unusually numerous. The single case 
of mosaic that occurred in the seed test can hardly be attributed to 
outside agencies, since soil and insects were eliminated almost beyond 
question and there was apparently no source of infection in the dis- 
trict adjacent to the experimental field. Furthermore, the very 
nature of the disease symptoms was such as might be expected in 
cases of seedling infection, the plant being much dwarfed and the 
first leaf showing signs of having been affected almost as soon as it 
appeared. 
Another case has occurred which is very similar to the above and 
lends support to the theory of seed as a means of overwintering. 
Seed was planted in the greenhouses of the plant-pathology depart- 
ment of the University of Wisconsin hi the fall of 1917, immediately 
after the houses had been thoroughly cleaned and fumigated and 
fresh soil placed in the benches. The planting was made on Septem- 
ber 12, using ordinary commercial cucumber seed, and the plants 
were under observation daily after they appeared. On Septem- 
ber 23, one plant out of 65 showed definite mosiac infection, the 
cotyledons were yellowed and wilted, and the first true leaf, which 
was very small, was mottled and distorted. (PL X, A.) The plant 
was proved to be infected by mosiac by the successful inoculation 
of several healthy plants from it. It was kept for several weeks in a 
separate house for observation and later developed the same peculiar 
wrinkling and yellowing observed in the case at Big Rapids. It 
remained much stunted and deformed. All the other plants grew 
vigorously and showed no signs of the disease. (PI. X, B.) 
In this case the factor of insect transmission can not be entirely 
eliminated, since hisects were present in the near-by fields until some 
time hi November, but the facts that no injury was visible on any 
plant hi the house and no insects could be found partly removed this 
objection, since slight injury of this kind is usually very noticeable 
on young seedlings. 
The results so far, therefore, show that out of 10,000 plants grown 
from seed from mosiac vines, only one has developed a case of mosaic 
that could not definitely be attributed to outside infection. Together 
with this is the case above noted, which appeared in the greenhouse 
under conditions that rendered outside infection very unlikely. The 
single case of infection which appeared hi the open field at Big Rapids, 
Mich., in 1915, is most easily explained on the basis of seed trans- 
mission, since no other infection developed in the field aside from that 
resulting from artificial inoculation. The field data aside from tnis 
