10 BULLETIN 1038, U. S. DEPARTMENT OF AGRICULTURE. 
Nishimura (55) found that the bladder cherry (Physalis alkekengi 
Linn.), after inoculation with tobacco-mosaic virus is capable of act- 
ing as a carrier without itself showing external signs of the disease. 
Cross-inoculation experiments (5) have shown that mosaics in to- 
bacco, tomato, pepper, and petunia are caused by the same infective 
principle. On the other hand, the mosaic of pokeweed (Phytolacca 
decandra Linn.) , though readily transmitted by expressed plant juices 
within the species, was not found to be cross inoculable on tobacco or 
vice versa (8). Tobacco mosaic is transmissible by insects. 
Another type of infectious mosaic is that carefully worked out by 
Baur (11-16) in the Malvaceae. He showed that the Abutilon 
mosaic is transmitted only by grafting and not by inoculation with 
the expressed juices, as occurs in tobacco mosaic. As in the latter 
disease, however, seed transmission does not occur. He found that 
when scions of the immune Abutilon arboreum Sweet are grafted 
on the variegated A, thompsoni Hort. they grow vigorously and re- 
main apparently normal. However, if scions of the green but sus- 
ceptible A. indicum Sweet are now grafted upon the immune A* 
arboreum they become infected and develop the typical mottling. On 
the other hand, the contagium passing through the immune A. arbo- 
reum is not capable of remaining there and giving infection if this 
portion of the shoot is subsequently grafted into a susceptible stock. 
In the case of the immune Lavateria arborea Linn., however, there 
is no transmission at all when double grafted between the mottled 
Abutilon thompsoni and the green susceptible A. indicum. Baur 
succeeded in transmitting this mosaic by grafting to about 50 species 
and varieties of Abutilon and related plants. 
It was found that if the leaves of variegated plants were removed, 
or if the shoots were cut back so that no leaves remained and the 
new shoots developed in darkness, only the first two or three leaves 
were mottled. If these mottled leaves were then removed the plants 
remained permanently green in the light unless they were grafted 
with scions from other variegated plants. However, if axillary buds 
on old parts were forced into growth these produced shoots with 
mottled leaves which in turn infected all the newly formed leaves 
on the plant. Furthermore, when scions of a green but susceptible 
variety were grafted upon defoliated, mottled plants the scions re- 
mained green ; but here again, if a mottled shoot was allowed to de- 
velop from the stock it rapidly infected the whole plant. The con- 
tagium is, 3 therefore, capable of infecting only the embryonic leaves, 
and in the buds it may be stored up for months in inactive form. 
3 The term " contagium " has been suggested by Dr. H. M. Quanjer as synonymous with 
any infective principle, whether of known or unknown origin. Its use in the place of 
" virus " with reference to the so-called " filterable-virus " diseases does away with ob- 
jectionable connotations and leaves nothing to be taken back. 
