6o6 ; MICROBIAL DISEASES OF PLANTS 



in securing satisfactory re-inoculatiohs. Subsequent studies* have 

 shown that this same microorganism is responsible for the pathological 

 condition that we recognize as cro^n gall in its various forms on the 

 different hosts. One of the remarkable things about this disease is 

 the large number of famiUes which, are subject to the infection. 



PATHOGENESis.r— A partial Hst of the plants upon which crown gall 

 occurs naturally or upon which it has been produced by laboratory 

 inoculation includes the daisy, tomato, tobacco, potato, carnation, , 

 peach, rose, cabbage, grape, hop, sugar-beet, turnip, red beet, carrot, 

 radish, chrysanthemum, oleander, marigold, pyrethrum, almond^ 

 clover, white poplar, Persian walnut, Pterocarya, gray poplar, cotton, 

 alfalfa, raspberry, geranium, apple, willow, quince. , 



Symptoms. — The swellings or galls, small at first, usually appear 

 just below the ground line (crown), at or near the juncture of the stock 

 and scion. These may be either hard or soft gaUs; the former are 

 smooth, soft, spongy, white to flesh-colored outgrowths which may 

 reach a very appreciable size during one season and then be entirely 

 decomposed and disappear by the following spring; the latter increase 

 in size more slowly, persist year after year, harden and become rough 

 and warty on the surface with age. Both are crown galls and both are 

 produced by bacteria. According to Smith, f "Whfether a crown gall 

 shall develop as a hard gall or a soft gall would seem to depend chiefly 

 if not altogether on which meristem cells receive the initial impulse. 

 If the cells first infected are principally the mother cells of medullary 

 rays, we may assume that the gall will be a 'soft gall,' and readily 

 incUned to decay. If, on the contrary, the needle or other carrier of 

 infection wounds principally those meristem pells which give rise to 

 tracheids and wood fibers, the gall will be a 'hard gall,' of slow growth 

 and long duration." The structure of the galls is unUke that of club- 

 root of cabbage in that the latter is an hypertrophy while the former 

 is an hyperplasia. Frequently this disease assumes a form known as 

 "hairy root" characterized by the presence of bunches or tufts of closely 

 matted rootlets with enlargements at their bases. As the gallsf enlarge, 

 the function of the adjacent conducting tissue is interfered with, and 



• Smith, Erw. F., Brown, Nellie A., Townsend, C. C, "Crown-gall of Plants: Its Cause 

 and Remedy," Bull. 213, Bur. Plant Ind., U. S. Dept. Agr., 1911. 



t Smith, C. O., "Further Proof of the Cause and Infectiousness of Crown Gall," Bull. 23s, 

 Calif. Exp. Sta., 1912. 



t Very hairy roots often accompany these. 



