74 SHADE-TREES IN TOWNS AND CITIES 



There is one phase of modern street-work that does not 

 tend to improve the highway trees, and that is the laying of 

 concrete walks. In order to lay these walks, there must be 

 an excavation of about eighteen inches, and if there are old 

 trees along the curb their roots are usually cut in the pro- 

 cess. Flag walks should be preferred in such cases. 



Frequently builders make it a practise to extend a strip 

 of concrete of the width of the stoop of the house from the 

 sidewalk to the curb. This is sometimes ten or twelve feet 

 wide, and this encroachment on the parking space takes 

 away still more from the possible nourishment of the tree, 

 that is already severely hedged in by the curb on one side 

 and the concrete walk on the other. It should be the desire 

 of builders to make suburban streets as countrylike as pos- 

 sible, and not to extend these concrete strips. 



Distance Apart of Specimens. Even after the proper 

 species has been selected there can be no greater mistake 

 in street-planting than setting trees too close together. The 

 distance between specimens should be such as to permit 

 them to develop perfectly, and the outstretching limbs 

 should not touch, even when the trees are fully grown. 

 Forty feet is about the average distance at which street- 

 trees should be set. The American elm should be set about 

 fifty feet apart; the sugar maple, the red oak, the chestnut 

 oak, and the oriental plane about forty-five feet apart; the 

 Norway maple and the red maple about forty feet apart; 

 the American linden and the pin oak about thirty-eight feet 

 apart; the European linden, the sweet gum, and the horse- 

 chestnut about thirty-five feet apart ; the gingko, the catalpa, 

 the hackberry about thirty feet apart ; the ailantus and the 

 Carolina poplar about twenty-eight feet apart. 



It must also be remembered in determining the dis- 



