30 BULLETIN 879, U. S. DEPARTMENT OF AGRICULTURE. 
cage as a partial shield during inoculation insects gained entrance 
very rarely. It was necessary to inspect all cages frequently to cut 
the tendrils which penetrated the cloth and to cover any small open- 
ings with heavy paint. All cages were set out as early in the season 
as possible, usually immediately after planting or by the time two 
to three leaves had appeared on the young plants. When plants ^ 
were caged after the disease appeared in the field they were left at 
least 10 days before being used in inoculation experiments, in order 
that any previous accidental mosaic infection might have time to 
develop before inoculations were made. 
Most of the cages used were of the same general type, the frame 
being of laths, with the exception of the corner uprights which were 
made of pieces from 1 to 2 inches square. In the earlier cages extra 
strips of lath were placed around the lower edge of the frame to allow 
it to be sunk 2 to 3 inches in the soil, but it was later found advisable 
to make the lower edges of light 4-inch boards. The cheesecloth i 
used contained 24 to 30 threads per inch, the lower edge of the cloth 
being* wrapped around strips of lath, which were then nailed to the 
bottom of the frame. Cages were also constructed with an opening 
in the top, but as they were difficult to build and often failed to remain 
insect proof, they were later abandoned, except for special purposes. 
Cages were used in practically all field work and reduced the factor 
of outside infection, which occurred only in rare cases, to a minimum. 
The caged plants grew luxuriantly and were only slightly affected by 
the shading of the cheesecloth. 
INOCULATION EXPERIMENTS. 
Inoculation of healthy vines with the juices of mosaic plants has 
proved that the causal agent of the disease is present in the tissues * 
of the stems, leaves, and fruits of mosaic vines. A light wounding 
of the plant inoculated is apparently essential for infection, as the 
virus does not seem to penetrate the unbroken epidermis. The two 
methods of inoculation used differ chiefly in the form of the inocu- 
lum, the expressed juice of mosaic plants or their crushed tissues 
being used. Results by either method have been successful, as is 
shown below. Control inoculations were made in all cases, using 
caged plants and inoculating them with the expressed juices or 
crushed tissues of healthy plants (PL IX, A). 
TESTS WITH EXPRESSED JUICES OF MOSAIC PLANTS. j 
In the earlier work the expressed juices of mosaic plants were used 
for inoculation. Portions of a mosaic plant, either leaves, stems, or 
fruits, were cut finely by means of a sterilized meat chopper, the 
juice pressed through cheesecloth, and in some cases filtered through 
filter paper, and the expressed juice used as the inoculum. The 
