88 
Journal of Agricultural Research 
Vol. XXV. Na * 
During the winter of 1919-20 in the greenhouse at Washington, D. C. y 
cross inoculations by leaf mutilation with mosaic between potato, tobacco,, 
and tomato indicated that the tomato was susceptible to potato mosaic, 
that the tobacco was susceptible to tomato mosaic but not to potato 
mosaic, and that the potato was not susceptible to tobacco mosaic. 
These reactions suggested that the tomato either responded sympto¬ 
matically to two different mosaic diseases or served as a necessary inter¬ 
mediate host for one mosaic between potato and tobacco and vice versa. 
Accordingly, in the winter of 1921-22 additional cross inoculations be¬ 
tween these hosts were made. In addition, cross inoculations with 
different types of potato mosaic were performed largely between potato 
and tomato in order to observe the reaction of the tomato to these dis¬ 
eases. The varieties used are indicated in Table XXII. Potato and 
tobacco plants at the time of inoculation varied in height from 8 to 15 
cm. and the tomato plants from 15 to 30 cm. Inoculations in 
each case were made by leaf mutilation. A single inoculation 
was made with the exception of Series 15, which received four applica¬ 
tions at weekly intervals. Inoculated and control plants came from seed 
pieces from the same tuber in the potato, and in the tomato cuttings and 
seedlings from the same lot. Inoculated plants and their controls grew 
in the same greenhouse, which was fumigated regularly for the control 
of aphids and white fly (Aleyrodes vaporariorum Westw.). The controls 
remained free from mosaic. 
The results shown in Table XXII indicate that the tomato is susceptible 
to tobacco and potato mosaic and that the symptoms vary between 
tobacco and potato mosaic, being filiform in part as a result of mosaic 
tobacco, and mild mosaic or simply mottling, ruffling, and wrinkling as 
a result of infection with mild mosaic of potato. 
Furthermore, the tomato reacted differently to the different types of 
degeneration diseases represented in the potato, being mild mosaic after 
inoculation with potato mild mosaic, and rugose mosaic with either rugose 
mosaic or with streaking plus mottling of potato. Tomato in Series 10 
showed the mottling of potato mosaic more readily than the potato itself; 
mosaic mottling in this case appeared in 12 days, while the potato had 
failed to show mottling at the end of 2 7 days. 
A comparison of Series 1, 3, and 15 discloses an apparent difference 
between potato mosaic and tobacco mosaic and suggests the harboring 
of two distinct mosaic diseases by the tomato. The mosaic tomato in 
Series 3 became infected from some unknown source, presumably by the 
potato mosaic in a separate greenhouse during the summer, while the 
tomato in Series 15 was inoculated with tobacco mosaic, which was not 
transmitted to the potato in spite of four repeated treatments, as the 
first and also second generation plants indicated. 
