346 MANUAL OF TREE DISEASES 



for the upward movement of water and raw food materials from 

 the roots to the leaves and for the downward movement of the 

 manufactured foods from the leaves to all parts of the twigs, 

 branches, tnmk and roots. If the bark and sapwood are injured 

 at any place to the extent that the tree is partially girdled, the 

 water and food materials pass with difficulty around the injured 

 area. Under some conditions, the limbs and roots directly 

 above and below the injury will suffer and may die. It is, there- 

 fore, necessary in all tree surgery work to conserve as much of 

 the living bark and sapwood as possible. Whenever these tis- 

 sues are exposed in the process, they must be immediately pro- 

 tected by a coating of shellac or they will soon dry out to such 

 an extent that the living cells will die. This precaution is es- 

 pecially necessary to protect the delicate cambium tissue which 

 lies between the bark and sapwood and is the formative region in 

 which these tissues are being constantly generated. 



Two results are accomplished by surgical methods ; first, the 

 unsightly diseased parts of the tree are removed ; and secondly, 

 the enlargement of the diseased area is prevented, and in the 

 case of diseases caused by living organisms, the source of further 

 infection is removed. Tree sm-gery may be divided into two 

 distinct types : by pruning, the affected limbs or roots are cut 

 off; and by lesion excision, only the affected area of bark or 

 wood is removed. 



Pktjning 



There are certain fundamental principles which must be ob- 

 served, if pruning is to be a successful eradication measure. The 

 work of pruning should begin at the top of the tree and the 

 greatest care must be taken to avoid injury to the bark during 

 the operation. Rubber-soled shoes should be worn by the 

 workmen. Iron-climbers, such as are worn to climb poles, 

 should never be used in trees. Ladders are the most effective 

 and least injurious means of reaching all parts of the tree. The 



