THE MOSAIC DISEASE OF CUCURBITS. 21 
tobacco plants, which often remain infectious for more than a year, 
even without the addition of preservatives. In the case of cucurbit 
mosaic the juices undergo rapid fermentation unless a preservative 
is added, but various chemicals, such as chloroform, ether, toluene, 
and glycerine, used at different strengths have never served to 
increase the time during which the juices remained infectious. Low 
temperatures have only a slight effect in prolonging the power of 
infection, and filtrates from Berkefeld filters in which no visible 
bacterial growth occurs are equally short lived in this regard. The 
preservatives used with the unfiltered juices were also tried with 
Berkefeld filtrates, but neither chemical preservatives nor low 
temperatures have any noticeable effect in prolonging their power 
of infection. 
EFFECT OF DRYING ON THE VIRUS. 
As the juices of mosaic plants rapidly lose their power of infection 
with age, it would be expected that drying would also remove this 
infective character. This has been the case with the tissues of mo- 
saic cucumber plants. The leaves of mosaic plants when dried at 
room temperature for periods of 10 days to 1 year have always 
failed to produce the disease. In these experiments the dried leaf 
tissues were pulverized and allowed to stand from 8 to 24 hours in 
a small quantity of sterile distilled water. The water extract was 
then filtered off and inoculations made both by the injection of the 
water extract into the stem and leaves of healthy plants and also 
by the insertion of the ground and moistened leaf tissue in wounds in 
the stems of healthy cucumber plants. A total of 49 inoculations have 
been made by these methods, but no infection has ever occurred. 
In addition to inoculations with dried leaf tissue, the dried stems, 
small fruits, and roots of mosaic plants were used in the same way 
as inocula in 38 inoculations, but always with negative results. The 
expressed juices of mosaic plants also lose their power of infection 
on drying. Experiments were made in which these juices were dried 
either on glass or on filter paper at room temperature. At intervals 
of seven days the dried material was taken up in sterile distilled 
water and the water extract pricked into the stems and leaves of 
healthy cucumber plants. Ten plants were inoculated from the 
dried material on glass and also from that on filter paper at the end 
of every seven days, the experiment being continued for five weeks, 
but no infection resulted from any of the inoculations. The result 
of experiments on soil transmission of the disease (p. 48) as well as 
the above data all indicate the rapid loss of the infective principle 
in the dried tissues of mosaic plants. 
EFFECT OF DILUTION ON THE VIRUS. 
The power of the virus of cucurbit mosaic to increase rapidly 
after its injection into the host tissue has been indicated by the 
rapidity of its distribution through the tissues of the plant inocu- 
lated. Further evidence of this rapid increase appears in the results 
