THE MOSAIC DISEASE OF CUCURBITS. 
41 
lar manner, but without crushing them. The results, shown in 
Table XV, indicate the ease with which infection may be brought 
about by this method. 
Table XV. — Infection resulting from successive handling of mosaic and healthy cucumber 
plants. 
Treatment. 
Number 
of plants. 
Results. 
Date. 
Number 
ofmosaic. 
plants. 
Date 
observed. 
Aug. 24,1916 
Do 
Aug. 11,1917 
Do 
Mar. 12,1918 
Do 
Leaves of diseased and healthy plants handled in suc- 
cession. 
Leaves of two healthy plants handled in succession 
(control). 
Leaves of diseased and health}- plants handled in suc- 
cession. 
Leaves cf two healthy plants handled in succession 
(control). 
Leaves of diseased and healthy plants handled in suc- 
cession. 
Leaves of two healthy plants handled in succession 
(control). 
5 
4 
6 
6 
10 
8 
3 

4 

6 

Sept. 4,1916 
Do. 
Aug. 30,1917 
Do. 
Mar. 28,1918 
Do. 
TRANSMISSION DUE TO CULTURAL OPERATIONS. 
TRAINING AND REMOVAL OF INTERTWINED PLANTS. 
The evidence reviewed above shows that handling may spread 
infection at any time, but it is more common later in the season 
when the plants have made a heavy growth. As the vines lengthen 
it is necessary constantly to train them back from the center of the 
row, and in picking they are also lifted and pulled about. These opera- 
tions produce many small abrasions, as the adjacent vines are usually 
interlaced, and when a mosaic and healthy plant occur together 
these slight wounds very often result in infection. It is commonly 
observed where few injects are present that the disease spreads 
along the row to the plants adjacent to the first isolated cases of 
infection. That this is due to such means as those mentioned above 
was strikingly demonstrated at Big Rapids, Mich., in 1916. The 
mosaic appeared at several points in a small field, and during the 
remainder of the season, in an effort to control it, all plants showing 
the disease were removed as soon as the first definite symptoms 
were observed. It was noted that, 10 days after the removal of the 
diseased individuals, plants in the same row and immediately adjacent 
to them began to show symptoms of mosaic, the disease progressing 
down the rows in both directions from the original diseased plants. 
In this experiment the vines were removed carefully, with the idea 
of avoiding infection, but slight injuries were unavoidable, and it is 
evident that such infection is constantly occurring throughout the 
season. It is probable that the factor of trichome infection is of 
special importance in cases of this sort, since the injuries need be but 
slight to produce infection through this channel. 
