PEAR DISEASES 341 
only a few feet may often be sufficient to determine whether 
the trees will be severely affected or not. (For a fuller dis- 
cussion of the question of frost-injury, see under Apple, page 
35.) 
Crown-GALL 
Caused by Bacterium tumefaciens E. F. Smith and Townsend 
The pear, like most other fruits, is affected with galls both 
at the crown and at the tips of the roots. While orchard trees 
show the enlargements, there is a greater tendency for nursery 
stock to be affected. In any case the destruction to pears is less 
rapid, and therefore less extensive, than to peaches or apples. 
Hairy-root, another form of the crown-gall disease, is less 
common on the pear than on other fruit-trees. Both the galls 
and hairy-roots may be induced by factors other than Bac- 
terium tumefaciens ; among such agencies may be noted (a) im- 
proper wrapping of grafts, (b) heavy applications of nitroge- 
nous fertilizers, and (c) the woolly aphis. A discussion of the 
galls, the causal factor, and remedial measures are treated 
more fully under Apple, page 108. 
REFERENCES 
Selby, A. D. Some diseases of orchard and garden fruits. 4. Root or 
crown gall of pear. Ohio Agr. Exp. Sta. Bul. 79: 127. 1897. 
Swingle, D. B. Fruit diseases in Montana. Crown-gall of pear. 
Montana Agr. Exp. Sta. Cire. 37: 317-318. 1914. 
Martin, G. W. The common diseases of the pear. Crown gall. 
New Jersey Agr. Exp. Sta. Cire. 52: 10-11. 1915. 
Eastern Rust 
Caused by Gymnosporangium globosum Farlow 
Pear rusts occur generally throughout the world. In the 
United States two important rust diseases of pear exist, but 
