THE MOSAIC DISEASE OF CUCURBITS. 49 
insure root injury as a point of possible infection. As controls, 40 
plants were transplanted into the same soil after it had been steril- 
ized with steam at 15 pounds' pressure for three hours. Plants 
grown in this soil, whether sterilized or not, remained healthy in all 
cases. 
During the month of August, 1916, a large number of mosaic 
cucumber vines were buried about 6 inches deep in sandy loam at 
Big Rapids, Mich., and left until the following year. In July, 1917, 
some of this soil containing the remains of the mosaic vines was 
taken to Madison, Wis., and used in the following experiments: 
(1) Cucumbers were grown in the soil directly from seed, and small seedlings were 
also transplanted into pots of the same soil. In each case, 25 plants were used, 
together with 30 check plants grown in the same soil after steam sterilization for three 
hours at 20 pounds' pressure. All plants remained healthy. 
(2) A 50-gram portion of the soil, containing a number of fragments of dried stems 
and leaves, was mixed with 50 c. c. of sterile distilled water and allowed to stand for 
12 hours. This extract was then filtered and the nitrate used to inoculate 10 healthy 
cucumber plants, inoculations being made into stems and young leaves. No infection 
occurred on any of the plants thus inoculated. 
(3) The remains of the vines present in the soil were removed, ground through a 
meat chopper, and enough sterile distilled water added to soak the material into a 
soft mass. Fragments of this were then inserted in incisions in the roots and stems of 
10 healthy cucumber plants, but no infection resulted. 
FIELD TESTS WITH CAGED PLANTS. 
While this work gave only negative results, more conclusive series 
of experiments were conducted in the field during the summer seasons 
of 1915, 1916, and 1917. Observations during 1914 at Hamilton, 
Mich., where mosaic had been severe for some time, showed that the 
disease seemed to occur as early and severely on new land as on fields 
where mosaic cucumbers had been grown for two or three years in 
succession. An attempt was made therefore, to determine whether 
fields that had previously grown mosaic plants furnished a source of 
infection for crops the following season. 
Hamilton, Mick., 1915. — One of the fields which had been under 
observation for two years was selected for work in 1915. The plat 
was one-eighth of an acre in size, had grown cucumbers for three con- 
secutive years, and nearly every plant had been diseased each year. 
This plat was again planted to cucumbers in 1915, and as soon as the 
plants appeared 18 cheesecloth cages were distributed over it, each 
cage covering two plants. The cages were lifted only once during 
the season, to allow weeding and thinning, and every precaution was 
taken to avoid outside infection. Mosaic appeared in the plat about 
July 20, and on September 6 every uncaged plant showed mosaic 
symptoms. The cages were lifted on this date and the entire 36 
plants were found free from disease. 
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