86 
Journal of Agricultural Research 
Vol. XXV, Not a 
toes and any other members of the Solanaceae is impossible, except the 
earlier grafting experiments of Quanjer (38, p. 42) with tobacco and potato. 
Transmission of mosaic from tomato to potato and from tomato to 
tobacco, and the reverse of each, has been reported by Quanjer (38, p. 
42). Here it seems possible either that a virus was involved, different 
from that of tobacco mosaic and those of potato mosaic in being infec¬ 
tious to all three hosts, or that the tomatoes were affected only with a 
combination of tobacco mosaic and potato mosaic. Later, Quanjer has 
reported transmission of common mosaic by grafting, from potato both 
to tomato and to tobacco (jp, p. 134 ): 
True infectious mosaic.can be transmitted by grafting to other solanaceous 
plants, e. g., tomato and tobacco. 
The details of his evidence are not given. Transmission of mosaic 
from a perennial weed, Physalis longifolia Nutt., to potatoes has been 
reported by Melhus {27). Quanjer has indicated the communicability of 
several degeneration diseases of potatoes to a considerable number of 
species of the Solanaceae (59, p. 132,134 , 136 ). The experiments to be 
reported here are with tobacco (Nicotiana tabacum L.)> tomato ( Lyco - 
persicum esculentum Mill.), and common nightshade (Solanum nigrum L.)- 
POTATO, TOBACCO, AND TOMATO 
Tobacco mosaic can be transmitted readily by means of a needle or by 
contact which breaks the trichomes (3, p. 613-17). The incubation 
period may be only 5 days (3,p. 613) and usually is no longer than 12 to 
15 days ( 2 , p. 17). Potato mosaic of the most virulent type has not 
been transmitted by inoculations approaching the needle method in mild¬ 
ness, and has a minimum incubation period of 12 days. With mild 
mosaic of potatoes unless inoculation is performed early and the growth 
period of the potato vines is lengthened by growing them either in a field 
insect cage or in the greenhouse, any infection that occurs will not as¬ 
suredly be apparent during the first generation. Either tobacco r osaic 
is caused by a more virulent contagium than any potato mosaic yet de¬ 
scribed, or, if its cause is identical with that of a potato mosaic, the symp¬ 
toms are greatly modified by potatoes. 
Experiments performed in the Orono greenhouse in the winter of 1919- 
20 are described in Table XXI. The tobacco plants grew from Connec¬ 
ticut Broadleaf seed, and mosaic was introduced both from dried mosaic 
tobacco leaves collected by Dr. W. J. Morse in Connecticut and from 
living mosaic tobacco plants sent from the greenhouse at Washington, 
D. C. The potato plants were of the Green Mountain variety and came 
from northeastern Maine. 
The data in Table XXI show that methods of inoculation adequate to 
transmit tobacco mosaic or potato mild mosaic within the species 
effected no apparent interspecific transmission. Leaf-mutilation juice 
transfer transmitted mosaic from diseased to healthy potato (Series 2 
and 13) and from diseased to healthy tobacco (Series 6) as shown in 
Plate 15, B, but not from diseased potato to healthy tobacco (Series 1 
and 12) or from diseased tobacco to healthy potato (Series 5 and 14). 
Spinach aphids transmitted mosaic from diseased to healthy potato 
(Series 4 and 8), but not from diseased potato to healthy tobacco (Series 
3) or from diseased tobacco to healthy potato (Series 7). The aphid 
colonies did not thrive on tobacco sufficiently for control aphid inocula¬ 
tions (diseased to healthy tobacco) to be made but Allard (5, p. 626-27) 
