BODY AND BRANCH DISEASES AND INJURIES 47 



gas- and soot-injury to the foliage; (2) unbalanced relation 

 between root and foliage system caused by cutting away sur- 

 rounding trees, or by injudicious pruning and pollarding; (3) un- 

 balanced water supply in the soil, caused by the physical con- 

 dition of the soil, or insufficient water reaching the roots due 

 to pavements and sod; (4) poisoning, due to natural or arti- 

 ficial gas escaping into the soil ; (5) mal-nutrition, due to lack 

 of certain essential food elements in soil or the over-balancing 

 of the food supply by improper use of fertilizers, which causes 

 toxic injury. Many of these tree troubles which are due to 

 unbalanced physiological processes, improper soil, site and 

 food supply, improper care in planting, pruning and the like, 

 and the relation of trees to their neighbors are purposely omitted 

 from discussion in this book. 



Fbeezing-to-Death of Twigs and Bakk 

 Caused by low temperatures 



Twig-blight due to freezing-to-death is common with certain 

 kinds of trees. Trees such as ash, oak, spruce and others 

 which cease twig growth early in the autumn and form ter- 

 minal buds, are usually resistant to freezing-injury. The wood 

 and bark of the twigs have sufficient time to mature and become 

 resistant to loyir temperatures. If, however, due to exception- 

 ally warm and moist conditions in the late autumn, growth is 

 resumed, the twigs may be severely injured by early frosts. 

 Other kinds of trees, such as basswood, sycamore and elm, 

 which do not naturally cease twig growth early in the autumn, 

 are injm-ed frequently by freezing. The twigs of the locust and 

 certain willows continue growing until late autumn and freeze 

 back every year. 



The injuries of bark due to extremes of temperature are 

 largely limited to those caused by freezing. Although condi- 

 tions which cause temperature injuries to the leaves have a 



