10 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
This bulletin embodies the results of that portion of the investiga- 
tion which relates to apple® trees. An endeavor is made to set forth 
clearly the nature of the disease and its effect upon trees in the nur- 
sery and the orchard, as well as to reeommend methods for its con- 
trol in the orchard. Of no less importance is the information for 
nurserymen resulting from a large number of experiments in nursery 
practice. Methods are given whereby loss caused by some forms of 
crown-gall and hairy-root may be either lessened or almost completely 
eliminated without greatly increasing the cost of growing trees in the 
nursery. Finally, it is shown by actual experiment that in the case 
of the milder and usual forms of the disease little or no injury is ap- 
preciable in young orchards. More intense forms, however, may be 
injurious, but in an orchard these rarely develop from the milder 
forms. No proof has been found that any of the forms are beneficial, 
as in case of the root tubercles of legumes. 
The writer has briefly described in this and in previous publica- 
tions a number of forms of crown-gali and hairy-root. There remain 
some points of doubt to be cleared up by other investigators, since 
this publication concludes the writer’s work on this subject. In the 
discussion which follows, for reasons given later and in order not to 
confuse the reader, all forms of crown-gall and hairy-root will be con- 
sidered as forms of the same disease. 
The results of many experiments are given, some of which were con- 
ducted in Missouri, Illinois, Iowa, Nebraska, Kansas, and Arkansas, 
and others in the District of Columbia and Virginia. It is necessary, 
for brevity, to say in the beginning that all experiments were prepared 
and conducted under the personal supervision of the writer and that 
all portions of each experiment were equally well prepared and cared 
for under similar conditions. Where such is not the case mention 
is made of the fact. | 
In the index to literature, on pages 93 to 96 of this bulletin, are cited 
all of the principal publications on apple crown-gall and hairy-root 
published in the United States, as well as many of those in other 
countries. A number of American and foreign publications on the 
subject of crown-gall deal with the disease on other hosts than the 
apple, and these have not been cited. 
Prior to July, 1907, the work of investigation was conducted in the 
Mississippi Valley Laboratory of the Department of Agriculture at 
St. Louis, Mo., under the supervision of Dr. Hermann von Schrenk. 
@ Owing to the confusion in the nomenclature of many of the common varieties of 
apples, all of the names used in this bulletin are in accordance with the ‘‘ Nomenclature 
of the Apple,’ by W. H. Ragan, Bulletin 56, Bureau of Plant Industry, issued January 
25, 1905. 
186 
