16 SHADE TREE GUIDE. 



Frost cracks, sun cracks, and winter kill. Extremely cold 

 weather, especially when it follows a late growing season, some- 

 times freezes the water in the outer cells of a tree stem and causes 

 a long crack. Thin-barked species, like sycamore and horse chest- 

 nut, are most susceptible and any tree on. a street, exposed as it 

 must be, is apt to suffer. Sun cracks have the same appearance but 

 are caused by excessive heat, often reflected from a white pave- 

 ment or wall. In large trees such cracks usually close again with 

 warmer weather and no serious harm is done, but the wood does 

 not unite and a scar is left. On small trees the crack is apt to per- 

 sist until new growth covers it. There is no practical preventive, 

 and no remedy other than helping nature by every care to heal the 

 wound. This can be hastened by treating the crack with antiseptic, 

 and keeping it from reopening by strong staples, driven in warm 

 weather when the gap is narrowest. "Winter kill" occurs when the 

 vital parts of a tree trunk are frozen and ruptured in a horizontal 

 plane by the formation of ice about its base. There is no remedy, 

 but the trouble can usually be avoided by having the ground slope 

 away from the foot of a tree on all sides so that no water can col- 

 lect there. "Winter kill" is common on the terminal shoots of many 

 trees and shrubs and rarely does permanent harm. 



Abrasions. Surface wounds, made by horses, lawn mowers, 

 blows, etc., are the starting places of most of the decay that de- 

 stroys shade trees. It is little realized that many serious tree wounds 

 originate between the nursery and the planting site. If the trunk 

 of a young tree is thrown on the side-board of a wagon the tender 

 bark and cambium are apt to be crushed, and tho the injury may 

 not show at the time the growth of the surrounding parts reveals 

 it. Every care should be taken to avoid these injuries. When one 

 occurs let the injured part be cut out carefully with a sharp knife 

 or chisel until sound wood is exposed and the edges left smooth. 

 Then sterilize and tar the wood not the cambium or bark, and leave 

 the rest to nature. Cement should not be used. (See F and H, fig. 

 n.) 



Cavities. Cavities in trees are invariably the result of decay. 

 They are treated with one or all of three objects in view: (i) to 

 stop the decay and induce healing; (2) to hide an unsightly part; 

 (3) to support a weakened body. The belief that every cavity 

 should be rilled is wrong, because, even with the best workmanship, 

 a filling merely retards decay, it does not stop it. The best rule is 

 to clean a cavity thoroly cutting out all decayed tissue with a 

 gouge and mallet until sound heart wood is exposed. If the cavity 

 will not hold rain water, or the wound is not unsightly, trim the 

 edges neatly, treat the wood surface and stop. 



