160 THE BOOK OF FORESTRY[ 



air, trees find it quite difficult. The fine dirt from the 

 pavements tends to clog the "stomata," the tiny breathing 

 pores on the under side of the leaves, so that the leaves, 

 the stomachs of the tree, find it hard to digest the food 

 which is brought to them. The above explains why 

 trees in the city often die from no particular disease 

 or attack of any kind. In addition, by lowering their 

 power of resistance these adverse conditions make trees 

 much more subject to insect and fungus attacks. The 

 forester must know the habits and resistance of his 

 trees in the forest and in the same way the city forester 

 or arborist, as he is sometimes called, must know which' 

 trees will survive in a given location. 



Duties of a City Forester. While the training re- 

 ceived at the average forestry school is intended to 

 fit men for tending timber forests, yet many such men 

 have gone into city forestry work because they knew 

 the life habits of trees. "When the need of officials to 

 look after trees was first felt by the cities, men were 

 often chosen for political reasons but on account of 

 the expert knowledge required it was soon found that 

 technical training was absolutely necessary. On ac- 

 count of the length of time it takes to grow a tree, 

 mistakes are extremely costly. If the wrong kind of 

 tree is planted or if not enough growing space is given 

 when trees are set out along a sun-beaten street much 

 valuable time is lost, hence a well trained city 'forester 

 can save much time and money. At present many of 

 the men in direct charge of shade tree and park work 

 are possessed of both technical training and experience. 

 Several institutions in the East are educating men along 

 these lines and in the best of them a thorough course in 

 landscape engineering is given, so that the entire prob- 

 lem of construction and maintenance of a shade tree or 



