430 ELEMENTARY STUDIES IN BOTANY 



135. Care of street trees. In observing most street 

 trees, one might infer that after the trees are planted they 

 need no attention. While they need little attention after 

 they are full grown, the young and growing trees cannot be 

 neglected. Perhaps the greatest cause of failure in the 

 growing of street trees is the poor physical condition of the 

 soil, a thing which the reader of this book might infer. The 

 soil, therefore, must be kept in good physical condition around 

 the young trees, and since the feeding ground of street trees 

 is much restricted, certain fertilizers are a great help. It is 

 evident that the cultivation of the soil beneath the tree 

 helps the movement of air through the soil and helps the 

 soil retain moisture. If there is sod around a tree, it should 

 be broken up every few years. 



Of course street trees must be pruned, and pruning is 

 done while the tree is dormant. In connection with pruning, 

 the large wounds (over two inches in diameter) must be 

 cared for, or they will permit the entrance of destructive 

 fungi. They are dressed with something that excludes 

 fungi, as thick paint or coal tar. When a wound is very 

 large (over six inches in diameter), it is usually covered after 

 treatment with a zinc plate, a process called " tinning." 

 Wounds less than two inches in diameter usually heal up 

 before the fungi effect an entrance. 



136. Injuries to city trees. There are many sources of 

 injury to city trees, due chiefly to city conditions. Smoke 

 poured out abundantly from smoke stacks, and gas from 

 leaking pipes escaping into the soil about the roots, are 

 common causes of dead and dying trees seen along streets. 

 Electric linemen are often reckless in chopping out branches 

 to clear the way for wires. Trees are also often seen to be 

 used for anchoring guy ropes. Regrading streets often de- 

 stroys trees ruthlessly and needlessly. Ignorant pruning 

 probably destroys more trees than any other danger, not 

 only because the pruning is wrong, but also because the 



