A Street Tree System for 1 New York City 53 



grows with a pithy center so that old trees often become 

 dangerously weak while still appearing to be in full vigor. 

 The habit of the tree can be much improved by formal prun- 

 ing, and when used as a street tree should not be allowed to 

 attain too large a size. The Ailanthus is recommended for 

 use especially south of 59th Street where growing condi- 

 tions are worst. The tree is dioecious, and the female form 

 should only be used, as the flowers of the male tree have a 

 disagreeable odor. It would probably be necessary for the 

 city to propagate the trees in its own nursery to make cer- 

 tain of the sex of the trees used. 



The following additional list is suggested as comprising 

 trees which might, under the most expert attention be grown 

 successfully on Manhattan streets, but only on streets where 

 conditions are most favorable. Such conditions would be 

 found on wide streets with generous gravel or grass parkings, 

 good depth of soil and where the buildings are moderately 

 low and the traffic light. 



1. Quercus rubra (The Bed Oak). 



2. Acer rubrum (The Red Maple). 



3. Fraxinus Americana (The American or White Ash). 



4. Ulmtjs Montana (The Scotch Elm). 



5. Ulmtjs Americana (The American Elm). 



6. Aesculus hippocastanum (The Horse Chestnut). 



