ALLARD: MOSAIC DISEASE OF TOBACCO 447 
In 1904 Selby (44) reported briefly his results with the mosaic 
disease of tobacco in Ohio. He reviewed some of the more 
important practical experiments conducted by previous investiga- 
tions and confirmed these results in some of his own experiments. 
He repeated a number of simple inoculation experiments with the 
virus of mosaic plants, and obtained symptoms of the disease in 
healthy plants after an incubation period of 9 to 12 days. He 
could see no difference in plants inoculated near the base and those 
inoculated in the tender portion. As a rule, the new growth alone 
showed the disease. He proved that a purely physiological 
chlorosis known as “yellow French” was not communicable to 
healthy plants by inoculation and that seed of mosaic plants pro- 
duced healthy plants. The disease could not be transferred to 
healthy plants through the blossoms by inoculating these with 
the nectar of diseased plants. Contact experiments conducted 
with diseased and healthy plants showed an increase of 68.6 
per cent. of disease in the healthy plants. In surrounding control 
plats the natural increase of the disease during this period was less 
than 3 percent. These experiments were a further confirmation of 
similar experiments previously conducted abroad by Hunger and 
Koning. 
Field observations in the Germantown district in 1903 and 1904 
gave interesting results with respect to the occurrence of the mosaic 
disease. Considering 12 farms in the vicinity of Germantown, 
the percentage of diseased plants ranged from less than 1 
per cent. to 43.5 per cent. On the station farm great variacion 
was found in the prevalence of the disease in individual rows, 
some rows being entirely free, others showing 56 per cent. of the 
plants affected. Fertilized and unfertilized plats showed no 
difference. Preventive measures are recommended which in the 
main consist of the prompt removal of all diseased plants, both in 
the seed bed and in the field. Selby states that such diseased 
plants if allowed to-remain become a menace to all healthy plants 
through the practical operations of worming, topping, suckering, 
ere, . 
In 1905 Hunger (46) further discussed the mosaic disease of 
tobacco. He carefully reviews the various theories of the disease, 
and gives a full discussion covering ‘‘ Pockenkrankheit,”’ which for 
