B. P. I.-186. v. P. P. I.— 145. 



II -THE CROWN-GALL AND HAIRY-ROOT DISEASES 

 OF THE APPLE TREE. 



By George G. Hedgcock, Assistant in Pathology, Vegetable Pathological and 

 Ph ysiolog ica I Investigations. 



INTRODUCTION. 



The diseases of the apple which have been classed under the name 

 crown-gall have, during the last few years, attracted much attention, 

 due partly to an increase of these diseases and partly to the enacting 

 of more stringent State laws governing the shipment and inspection of 

 trees. 



A series of investigations into the nature of crown-gall upon the 

 apple, pear, raspberry, peach, almond, grape, rose, and other plants 

 has been in progress for some time in the Mississippi Valle} T Labora- 

 tory of the Bureau of Plant Industry at St. Louis, Mo. , and also at 

 other points in the Mississippi Valley. It is not to be assumed, how- 

 ever, that such diseases are more common in this localit}^ than in some 

 other portions of the United States. Apple crown-gall and hairy -root 

 have been found in all nurseries that have been examined in various 

 portions of the country. 



This preliminary report is sent out, not with the intention of giving 

 the results of all our investigations, but for the purpose of calling the 

 attention of apple-tree growers to the different diseases hitherto known 

 as apple crown-gall, and to endeavor to interest them in the collection 

 of data regarding the predisposition of varieties to these diseases. 



TWO DISTINCT DISEASES, CROWN-GALL AND HAIRY-ROOT. 



Our investigations have resulted first in separating apple crown-gall 

 into two diseases, which are considered distinct. The disease now 

 designated as crown-gall is a callous-like gall growth of hypertrophied 

 tissue following wounds on some portion of the root system of the 

 tree, which rarely occurs above the ground on parts of the trunk or 

 limbs. (See PI. Ill, figs. 1 and 2.) 



The malady now called the hairy-root disease is evidently the same 



as the one first given this name by Stewart, Rolfs, and Hall in Bulletin 



191 of the New York State Experiment Station. It is characterized 



both in seedlings (PI. IV, fig. 1, and PI. V, fig. 2) and in grafted or 



16976— Xo. 90—06 3 15 



