112 MANUAL OF FRUIT DISEASES 



apple, but from many other plants, including the almond, apricot, 

 beet, blackberry, cherry, chestnut, clover, cotton, daisy, English 

 walnut, grape, honeysuckle, hop, lettuce, peach, plum, poplar, 

 potato, prune, quince, rose, tobacco, tomato, turnip and willow. 

 This list is incomplete but will give an idea of the wide range of 

 plants susceptible to the disease, and therefore of the many 

 sources from which the bacteria may come to the apple. 



Control of crown-gall. 



In dealing with crown-gall, the following points should be 

 borne in mind: (1) the great number of plants attacked; 

 (2) the identity of the bacteria causing hairy-root and crown- 

 gall ; (3) the greater abundance of the disease in nursery-stock ; 

 (4) the bacterial nature of the disease ; (5) the entrance of the 

 pathogene into the host through wounds ; (6) its presence in the 

 soil; (7) the distribution of the pathogene in nursery-stock; 

 (8) internal infection by tumor strands, and that therefore not all 

 galls necessarily arise from an external source. In the light of 

 these data the following measures and precautions should be 

 employed : (1) deep planting to protect the plant a'gainst 

 frost-injury; (2) avoid injuries to the roots and stems; (3) re- 

 move diseased trees; gall excision is unsatisfactory and un- 

 reliable; (4) protect grafts at the point of union by using a 

 root and scion of approximately the same size, and by wrapping 

 them carefully ; (5) reject diseased nursery-stock. (See Table 

 of Contents for other fruits which are affected by crown-gall.) 



REFERENCES 



Smith, E. F., Brown, N. A., and Townsend, C. O. Crown-gall of 



plants: its cause and remedy. U. S. Agr. Dept. Plant Indus. 



Bur. Bui. 213 : 3-215. 1911. 

 Smith, E. F., Brown, N. A., and McCulloch, L. The structure and 



development of crown gall : a plant cancer. U. S. Agr. Dept. 



Plant Indus. Bur. Bui. 255 : 3-60. 1912. 

 Swingle, D. B. Fruit diseases in Montana. Crown-gall of apple. 



Montana Agr. Exp. Sta. Circ. 37 : 290-301. 1914. 



