196 



Fkost Cracks. 



Frost cracks are sometimes found disfiguring and injuring 

 fruit trees by splitting the bark and wood of the limbs. In 

 some cases they open only one-half inch or so, while in 

 severe cases they may be three or four inches wide. They 

 occur usually during sudden reductions in winter tempera- 

 ture. Extreme cold has a similar effect on the tissue to dry- 

 ing or shrinking, by causing a withdrawal of water from the 

 cell walls, thus rupturing the tissue, and while the cracks 

 sometimes heal over, they more often do not. They open 

 wide in winter, and their opening and closing are aifected by 

 various meteorological conditions. 



Frost cracks are very difiicult to treat, but we have found 

 that the best way to handle them is to paint the inner surfaces 

 of the cracks with coal tar or paint in winter when they 

 open up. Then in spring or summer, when the cracks close, 

 staples of one-half or five-eighth inch iron, with prongs three 

 or four inches long and pointed ends, may be driven into the 

 trees after boring a hole with an auger. The staples should 

 be painted and the bark cut away underneath, so that they 

 may be driven in flush with the wood, when they will heal 

 over and disappear. 



Fkost Blisters. 



Occasionally during the past ten years we have observed a 

 spotting on apple leaves caused by injury from spring frosts, 

 and during the summer of 1902 considerable defoliation re- 

 sulted, as much as 30 per cent, of the leaves falling from 

 certain trees in July and August. The trouble was in gen- 

 eral confined to the sections where the spring frost was most 

 severe. 



This frost injury occurs just as the leaves are unfolding, 

 the frost rupturing the tender epidermal cells on the under 

 side of the leaves. As the leaves develop, conspicuous, ir- 

 regular spots may be found on the upper surface, corre- 

 sponding in a general way to the ruptured areas on the under 



