146 THE CULTIVATED EVERGREENS 



importance in that they provide avenues for the entrance of 

 fungi which may cause serious wood-rots. 



Cracks of this type will usually heal over naturally unless 

 they are repeatedly reopened by low temperatures. The 

 healing may be hastened, however, by using staples to close 

 the wound. The exposed surfaces of wood and bark should 

 be sterilized and waterproofed (see under tree surgery) in the 

 winter when the crack is wide open. The stapling should be 

 done in the spring when the wound is closed. Staples may be 

 made of iron, about three-eighths of an inch in diameter, and 

 should be four to five inches wide and about the same length. 

 The bark and wood is removed to allow the staples to be 

 driven in flush with the wood, and the exposed tissue should be 

 treated with creosote and tar or thick bark-colored paint. 

 The staples should be about two feet apart, and better results 

 will be obtained if the points are bent slightly inward. 



Sun-scorch. 



This is also similar to the trouble described under the same 

 name in connection with seedling diseases. In its effects it 

 resembles winter-drying, but it occurs during the summer 

 months. It usually becomes evident after high winds on hot 

 days. The needles on the exposed side of the trees become 

 yellow and then brown from their tips, giving the tree a 

 scorched appearance. Norway spruce, Douglas fir, pines, 

 white-cedar, and arbor- vitse are more commonly affected. 



Sun-scorch is a result of drought conditions brought about 

 by excessive transpiration. To a considerable extent such 

 injuries are unavoidable, but they may be lessened by any 

 measures which tend to keep the soil moist and well aerated. 

 Mulching, when practicable, is beneficial, especially when 

 combined with artificial watering. 



