The Winter Injuries 299 



or galls, that have been the subject of much uneasiness 

 with fruit-growers; these galls are contagious, being 

 produced by a soil bacterium. The "hairy root" of apples 

 and pears is a form of the same disease. The organism 

 attacks many kinds of plants. It is now thought they do 

 not often produce great injury in the orchard, but they 

 are always to be avoided, and trees with galls would better 

 not be planted. 



The root-knot of the southern states and of greenhouses 

 is a wholly different trouble, and is the work of a nematode 

 worm. There is also a root-swelling or gall on raspberries, 

 due to the work of an insect. The nematode galls are 

 commonly smaller and softer swellings, and occur on the 

 younger or smaller roots, and appear not to be found in 

 the open in regions where the ground freezes deep. 



WINTER-KILLING 



There are two distinct types of injuries to fruit-plants 

 by cold, — ^true winter-killing (or the injury of the tree or 

 buds when perfectly dormant, by the low temperature of 

 winter), and the killing of the growing or swelling 

 parts by the "cold snaps" or frosts of late spring and 

 early fall. 



Winter-killing of the wood. 



Three factors chiefly appeal to the fruit-grower in the 

 winter-killing of trees, — ^positive cold, very dry or very wet 

 soil, and heaving of the land by frost. The subject of "dry 

 freezing" has already been mentioned in Chapter I as a 

 danger in the mid-continental country. The heaving of 

 the land is prevented by drainage, by proper methods of 

 tillage, and by the judicious use of cover-crops. The 



