ROOT DISEASES AND INJURIES 75 



Symptoms. 



The symptoms of freezing-to-death in the roots, as noticed 

 in the aerial parts, are general, although somewhat distinctive 

 and diagnostic. The primary symptoms can easily be deter- 

 mined by examining the roots themselves. Tissue which has 

 suffered from freezing-to-death gives no external evidence of 

 its condition until some time after it has thawed. Then it ap- 

 pears, at first, water-soaked and later, after some disintegration 

 processes have set in, it becomes brown. Tissue thus killed is 

 soon invaded by the numerous saprophytic organisms in the 

 soil and is further disintegrated. 



Severe injury to the entire root system results in the death of 

 the tree before summer. The leaves may come out, but re- 

 main small and misshapen. Less severe and re-occurring in- 

 jury to the roots may result in a varying succession of symptoms. 

 One of the most common effects is that of sun-scorch of the 

 leaves, and is most common in the pine and maple (see page 22). 

 The inability of the remaining healthy roots to provide enough 

 water for the leaves to equal the amount transpired on hot days 

 results in the wilting and death of the leaves. The entire tree 

 suffers then, since the diminution of the leaf-surface makes im- 

 possible the manufacture of enough food materials for normal 

 growth. Another symptom of root-injury is the production 

 of thin foliage at the top, in excurrent trees, and stag-head may 

 be the cumulative effect of this condition. 



Cause of freezing-to-deatJi. 



In the process of maturing the new tissue formed during the 

 summer, the roots are the last part of the tree to attain the con- 

 dition necessary to withstand low temperatures without injury. 

 A combination of a late warm autumn followed by deep freez- 

 ing of the ground may lead to serious root damage. Thus, it 

 happens that winter-injury to the roots is exceptionally common 

 some winters and rare in others when the temperature falls to 



