B. P. 1.—580. 
FIELD STUDIES OF THE CROWN-GALL AND HAIRY- 
ROOT OF ithe AP Th En. 
INTRODUCTION. 
Growers of fruit trees have noted for many years a diseased con- 
dition of apple trees which usually manifests itself on young trees 
in the formation of galls and of clustered or fasciated roots at or near 
the surface of the ground, and on older trees in the form of knots 
or tumors occurring on the branches. These forms of disease have 
been variously designated as ‘‘galls,”’ “crown-gall,” ‘“crown-knot,”’ 
“hairy-root,”’ ‘woolly-knot,” ‘woolly-root,” “broom-root,” ‘root 
knots,” “‘root galls,’ and “‘tumors.”’ 
In recent years these forms of the disease have been brought promi- 
nently before the public by a number of investigators. As a result of 
the consequent agitation, following statements alleging their danger- 
ous nature, many States have enacted stringent laws for prevention 
and control. Although such laws, as a rule, should be enacted as a 
matter of precaution, in this case they have entailed great hardship 
and loss tonurserymen. An estimate of this loss, based upon reports 
received from leading wholesale nurserymen in various parts of the 
country, places the amount at not less than half a million dollars 
annually. The actual loss to orchardists is uncertain. In fact, data 
from exact and careful orchard experiments have not hitherto been 
available. 
A very unsatisfactory condition has arisen from the widely diver- 
gent opinions of observers relative to the communicability of crown- 
gall and to its effect. State laws upon the control of these forms of 
disease vary as much as the opinions of those who have made observa- 
tions upon their effect. Consequently, there has arisen an urgent de- 
mand from nurserymen and horticulturists for more exact data on 
their nature. In response to this demand, a series of studies and ex- 
periments, embracing the greater portion of the United States, has 
been conducted by the writer for a continuous period of seven years. 
This investigation has included the forms of disease ordinarily known 
as “crown-gall” and “hairy-root” attacking many kinds of trees, 
vines, and shrubs, embracing a study of the cause, communicability, 
effect, and extent of the various forms of disease. 
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