252 State Horticultural Society. 



CROWN-GALL AND HAIRY-ROOT DISEASES OF THE AP- 

 PLE TREE. 



(By Herm.'imi Von Schrenk and George Grant Hedgcock.) 



Crown-gall, as it has hitherto been known to nursery inspec- 

 tors, includes what is now considered three distinct forms of disease 

 on apple trees. The form corectly named crown-gall is a callous- 

 like gall growth of tissue following wounds on some portion of the 

 tree, usually below the surface of the ground, but not always. It 

 has been found by experiment that there are two forms of crown- 

 gall, the one of a hard, woody nature, which tends to form a bark 

 approaching that of normal tissue; the other of a softer nature, 

 tending to rot away whenever the tissues suffer injury or under un- 

 favorable soil conditions. Trees which have the hairy-root disease 

 form a superabundance of fine roots, and often lack roots of normal 

 size. Three types of this disease have been noted. These are still 

 under investigation, and for the present will be considered as one. 



The hard crown-gall of the apple frequently occurs at the 

 union of the scion and root on grafted trees, and consists of a super- 

 abundance of callous tissue, formed usually from the lower end of 

 the scion. In some varieties of trees, like Wealthy and Missouri 

 Pippin, hard galls or knots are apt to occur at any point on the scion 

 on or below the surface of the ground where an injury is received; 

 they also often develop from buds on the scion. In a few instances, 

 such galls have been noted upon trees above the ground, even upon 

 the limbs and higher portions of the tree. Experiments with a 

 very large number of trees indicate that this form of crown-gall is 

 not contagious ; it does not appear to hinder the growth of the tree, 

 except where the tissue entirely involves the root of the tree ; t^ier. 

 it apparently interferes to some extent with the movement of sap, 

 tending to retard it. In the case of the Wealthy apple, the most 

 vigorous trees quite often have one or more of these knots on the 

 scion portion in grafted trees. An experimental orchard, planted 

 with healthy trees and with trees diseased with this type of knot, 

 was planted three years ago last spring. No apparent difference 

 can be noted in the growth of the trees; it cannot be said, how- 

 . ever, that such growths are beneficial to the tree; neither do we 

 consider a galled tree as good for planting as a smooth tree, only 

 the latter form being considered perfect. 



The soft gall of the apple tree in its earlier stages, like that on 



