12 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
DISTRIBUTION OF THE DISEASE AND RELATED FORMS. 
GEOGRAPHICAL DISTRIBUTION. 
The hard and soft forms of crown-gall on the apple tree and on 
various other plants have either been observed by the writer or 
reported to him by others in practically every State in the Union. 
The writer has found both forms of the disease on apple trees in every 
locality where nurseries were inspected by him, and in many where no 
nurseries were located. The disease, in both forms, is most abundant 
in the more southern States of the apple-growing belt, from Virginia 
to Texas. The writer collected data in 31 States and Territories and 
received reports of occurrence from correspondents in all of the others 
except Nevada. 
In Europe, as previously mentioned, crown-gall or a similar disease 
(Wurzelkropf) occurs on apple and pear trees in Germany. The 
writer finds it common on apple seedlings imported direct from Hol- 
land and France. W.S. Blair, in a letter, reports its occurrence in 
Ontario, Canada, on apple trees. 
The forms of the disease known as hairy-root have been found as 
widely disseminated as crewn-gall on apple trees in nurseries and 
orchards in the United States. In orchards hairy-root is more com- 
mon than crown-gall. 
In Europe the aerial form of hairy-root or a similar form (Kropf- 
maser) occurs on apple trees in Germany (60). W. S. Blair, by 
letter, reports the occurrence of hairy-root on the roots of apple trees 
in Ontario. Hairy-root of the simple and of the woolly-knot form has 
been found by the writer on trees imported into the United States 
from New Zealand. 
DISTRIBUTION IN NURSERIES. ~ 
In seedling nurseries apple trees are grown for one season from seed, 
then dug and used for propagation in budding and root grafting. 
The writer inspected the stock at the time of digging in a number of 
the largest seedling nurseries in Kansas, Nebraska, Iowa, and Mis- 
sourl. In one lot of 300,000 apple seedlings examined, sorted, and 
and counted under his supervision, less than one-half of 1 per cent 
was diseased with crown-gall, almost entirely of the soft form, and 
about 1 per cent with hairy-root, chiefly of the simple form. This 
percentage holds good for all of the nurseries examined. 
In nurseries where trees are propagated by budding and root grait- 
ing, as compared with seedling nurseries, there is a much greater per- 
centage of disease. On trees grown from root grafts there is more 
disease than on those propagated on seedlings by budding. The rela- 
tive percentage of disease of each form found on budded and grafted 
trees in nursery experiments is shown on pages 18 and 19. 
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