POTATO WILT, LEAF-ROLL, AND RELATED DISEASES. 43 
In 1912, it was exceedingly prevalent in some fields of Green Moun- 
tain in Aroostook County, Me. The number of plants affected 
varied from 1 per cent up to practically 100 per cent. Some fields 
of several acres were seen where hardly a normal plant could be 
found. The disease was present again in 1913 in the same district, 
always on the Green Mountain variety. Mosaic has not been found 
in the potato districts of Wisconsin, Minnesota, Colorado, or other 
Western States, though an extended survey of these States was 
made in 1912 and 1913. 
There is evidently much difference in varietal susceptibility. 
Hundreds of fields were examined in Maine where the Green Mountain 
variety was growing side by side with Irish Cobbler, but practically 
no mosaic was observed in the latter, whereas it was very common in 
the former. There appears to exist also a corresponding difference 
in the tendency of strains or stocks of the same variety toward mosaic. 
Different fields of the Green. Mountain variety showed from none to 
100 per cent of diseased plants. An experiment in the Arlington 
greenhouses further demonstrated this point, though undertaken for 
another purpose — the control of silver scurf. Two greenhouse beds 
were planted with the variety Eureka, using seed from two sources. 
One lot showed 46 mosaic and 31 healthy plants, eliminating doubtful 
cases, or 59.7 per cent diseased. The second lot had 100 per cent 
free from mosaic. Portions of the first lot had been treated with 
formalin, corrosive sublimate, and heat, with control lots untreated. 
These treatments did not appreciably affect the proportions of 
mosaic which developed. 
That mosaic is transmitted through the tubers is thought to be not 
improbable. An experiment to test this was carried out in Maine 
during the past season with somewhat inconclusive results. Tubers 
from mosaic hills marked in 1912 were planted in hill-unit rows, with 
controls. The progeny were in part mosaic and in part of a doubtful 
character, smaller and less vigorous than the controls, but with less 
clearly marked mosaic than the parent hills. On account of some 
confusion of the labels, it is thought best to repeat the test before 
drawing conclusions. 
The cause of potato mosaic is unknown, nor have experiments been 
made to determine whether, like the mosaic of tobacco, it is commu- 
nicable from plant to plant. Allard (1912) has shown that the tobacco 
mosaic can not be transferred from tobacco to potato by inoculation. 
The exact nature and relationship of potato mosaic to other similar 
troubles remains to be worked out. In this article, which is primarily 
diagnostic, it is aimed to point out that such a disease exists and 
that it may become a factor in the problem of varietal deterioration 
of such importance as to require consideration when selecting or 
inspecting seed stocks for certification or purchase. 
