INJURIES TO TREES. 109 
exert too great a leverage, the losses may be reduced to a mini- 
mum. Trees having brittle wood or weak crotches, as the Soft 
Maple, are much more liable to this injury than those with 
tough wood, as the willows, oaks and elms, and need more 
pruning on this account. Evergreens are likely to be broken 
Figure 25. Trees heavily loaded with ice after a sleet storm. 
by heavy snows that freeze on the leaves. This may be pre- 
vented on lawn and shade trees by shaking the snow off from 
them before it freezes. 
Frost Cracks are a rather infrequent injury caused by the 
cracking of trees from center to outside, due to uneven contrac- 
tion in very cold weather. It is generally accompanied by a 
loud report. Such cracks are often eight or ten feet long, and 
occasionally longer. They generally close up again when the 
wood thaws out, and during the following summer grow over, 
