Apr. x, Z93X 
Leafroll, Net-Necrosis , and Spindling-Sprout 
49 
necrosis of the net type may have a similar appearance, but the writers 
have not found any frost-necrosis of the ring or blotch types in their 
net-necrosis material and have found, as reported by Jones and others ( 12 , 
p. 36, 45), that frost-necrosis induced experimentally (PI. 4, B) was not 
accompanied by any of the symptoms characteristic of leafroll. 
SPINDLING-SPROUT 
As with other descriptive names for diseases for which no pathogene 
has been described, it is quite probable that with “spindling-sprout” 
more than one cause is involved. The type considered in this paper is 
shown in Plates 3, B; 4, A, C; and 5, A. 
GEOGRAPHICAL DISTRIBUTION 
It may be inferred from the reports on the distribution of leafroll that 
it occurs wherever the Irish potato is grown. Orton (15) mentions its 
occurrence in Austria-Hungary, Denmark, Germany, Holland, Sweden, 
Switzerland, and the United States. It is also reported to be in France 
and Java (17). Collaborators for the Plant Disease Survey (rr, p . 33) 
have noted its occurrence in the States of California, Colorado, Connecti¬ 
cut, Georgia, Idaho, Iowa, Maine, Maryland, Massachusetts, Michigan, 
Minnesota, Montana, Nebraska, New Jersey, New York, Ohio, Oregon, 
Pennsylvania, South Carolina, Tennessee, Utah, Vermont, Washington, 
and Wisconsin. Wortley (24) states that he examined more than 60 
varieties of potatoes affected by this disease in America—in the East 
from Florida to Maine; in the Middle West and West in Michigan, Minne¬ 
sota, and Colorado; in Canada in the Provinces of Ontario, Quebec, New 
Brunswick, Nova Scotia, and Prince Edward Island; and in Bermuda. 
Data are very few concerning the extent to which net-necrosis is found 
geographically. Reference to Table VI, and to the authorities already 
quoted in regard to the symptoms shows that it is found generally in 
Maine and at least to some extent in other States. A form of spindling- 
sprout may sometimes be a result of net-necrosis, as will be shown later, 
and so may possibly be found wherever the latter disease appears. 
ECONOMIC IMPORTANCE 
Estimates made by the collaborators of the Plant Disease Survey (ri, 
P • 53 ) show that in the United States the percentage of plants affected 
with leafroll may range from 1 to 95. The presence of the disease in 
almost all the potato-growing sections, including the most important 
seed-growing centers, produces a very favorable condition for its con¬ 
tinued spread. This is more particularly the case where the agents of 
its dissemination are most abundant, as indicated in the following pages. 
Leafroll causes considerable losses wherever an appreciable percentage of 
the plants are affected, because diseased hills produce tubers which may 
be greatly reduced in size and number. Plants severely diseased will 
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