Atmospherical Influences 67 



and a thinning of the top, or in under-development of the 

 foliage, the latter being smaller, assuming a pendulous 

 position and early fall coloring. 



The best preventive, where this kind of loss is anticipated, 

 consists of pruning and mulching well, in order to restore 

 the proper balance between root and crown. 



Winter cold will, of course, affect the young and imma- 

 ture twigs in the same way as do the late frosts. 



In smooth-barked trees, such as the Beech and Horse- 

 chestnut, and in special situations, the bark of branches and 

 young trees cracks in patches, and the cambium and the 

 young wood underneath are killed. If such lesions are 

 extensive they may lead to the death of branch or tree. 

 This injury generally takes place on the southwest side and 

 toward the end of winter when rapid temperature changes 

 are more common; a few warm days stimulate the cambium 

 on the south side to premature activity; freezing weather 

 following, these active areas are killed, the young wood 

 cells and cambium shrinking away from them and the bark 

 cracking and drying out. Often not until summer does 

 the bark split and reveal the damage below. 



Such frost phenomena as the killing of the bark appear 

 in very variable form, such as small frost hoils, or smaller or 

 larger frost plates, the dead bark splitting off from the live 

 margins and rolling back, exposing the dead wood, which 

 then is either gradually covered up by a callus from the 

 marginal cambium, or else becomes infested by fungi. 



The worst form of these frost injuries is the malformation 

 known as canker, in which fungus parasites also take part. 

 Wet, cool localities seem to predispose trees to this disease, 

 but severe pruning and manuring in the spring may produce 

 the same effect; this curiously enough, seems to appear 

 as an individual peculiarity which can be transmitted by 



