July i, 1925 Overwintering and Dissemination of Cucurbit Mosaic 
3 
Field Trials of 1919 
The seed used in these trials was collected by M. W. Gardner at 
Grass Lake, Mich., and Sparta, Wis., in the summer of 1918, from 
fruits which showed symptoms of the mosaic disease. The seed 
from each fruit was removed and planted as a separate lot. The 
trial plat was located at Ellison Bay, Wis., in the northern part of 
Door County, where mosaic was not known to occur and where 
cucumbers were not planted extensively. Approximately 10,000 
seeds from 77 fruits were planted on June 20, but owing to the low 
percentage of germination, only 3,400 plants were obtained. These 
plants were kept under observation during the summer and in¬ 
spections of the individual plants were made on July 11 and 26. 
Each plant was carefully examined and inoculations were made from 
16 plants which showed abnormalities of growth or leaf color. None 
of these inoculations produced mosaic ana no evidence of the disease 
appeared on any of the plants during the season. 
Greenhouse Trials 
Studies of the relation of temperature to the development of 
cucurbit mosaic have shown that the disease develops most rapidly 
at temperatures of about 30° C., and it was decided, therefore, to 
conduct trials of seed from mosaic plants at the temperature which 
seemed most favorable to the development of the disease. 
TRIALS OF 1920 
Seed collected from mosaic cucumber plants at Madison in 1919 
was planted during the winter in two greenhouses held at tempera¬ 
tures of approximately 24° and 30° C., respectively. The tempera¬ 
ture was kept reasonably constant within limits of 2° in the house at 
30° and with a variation of 5° in the other house. Plants from the 
seed of each fruit were grown in each of these houses, the two tem¬ 
peratures representing the optimum for the disease at 30° and an 
approximate optimum for the plant at 24°. The seeds were planted 
in duplicate flats of steam-sterilized soil, each flat containing 25 
seeds from each of four fruits. A total of about 3,500 seedlings were 
obtained from the seeds of 77 fruits during the winter. The plants 
were kept until three leaves developed and were allowed sufficient 
room in the flat for normal growth. No other cucurbits were grown 
in the greenhouse used for these experiments and the houses were 
fumigated regularly in order to guard against infection by insects. 
No mosaic developed during, these trials and the plants made normal 
growth in all cases. 
TRIALs[ OF 1921 
During the winter of 1920-21, further trials were carried on in the 
greenhouse, using seed from the same source and growing seedlings 
from each fruit in duplicate series at air temperatures of approxi¬ 
mately 30° and 24° C. Two series were conducted during the 
winter and early spring, a total of 2,200 plants being under observa¬ 
tion during this time. The plants made normal growth and failed 
to show any symptoms of mosaic during the trials, although they 
were kept until the third leaf was well developed. 
