-76 MANUAL OP TREE DISEASES 



even a lower point. The injury caused to the roots is the tj-pe 

 known as freezing-to-death (see page 12). The water in the 

 cells is withdrawn dining the formation of ice crystals between 

 the cells. As the temperature becomes lower, the physical pull 

 incident to ice formation causes a larger amoimt of water to be 

 withdrawn from the hving cells than they can endiu"e without 

 being killed. Since the root system of most kinds of trees may 

 extend from a few inches to several feet below the surface, it is 

 natural that shallow-rooted trees will show the first and most 

 serious injury provided the miniTnnm temperature for the roots 

 of that species is reached. Also, the amoimt of damage to the 

 root system of a given tree depends on whether its roots are 

 largely superficial or are found at varying depths. 



Control. 



Winter-injured roots should be uncovered and the dead parts 

 pruned off. The wounds should be treated with a wound- 

 dressing, and the soil conditions around the tree made con- 

 ducive to the rapid regeneration of new roots by fertilizing. 

 Mulching may be practiced to protect the soil around sus- 

 ceptible trees from freezing deeply. 



Refebence 



stone, G. E. Winter injuries of roots. In Shade trees, character- 

 istics, adaptation, diseases and care. Massachusetts Agr. Exp. 

 Sta. Bui. 170 : 200-204. 1916. 



G.\S-IXJURT 

 Caused by illuminating gas 



Trees are commonly injured by the poisonous effect of illumi- 

 nating gas on the roots, when leaks in gas-pipes are not promptiy 

 repaired. The effect is usually cumulative and the tree may 

 show no sign of the injiu-y until some time has elapsed. 



