98 SHADE-TREES IN TOWNS AND CITIES 



tree. They are placed on a level with the pavement and are 

 supported by wooden pins driven in the ground. The soil 

 under the grill is left depressed or basin-shaped, the deepest 

 portion being that farthest from the base of the tree. This 



Fig. 14. — Method of placing grill. The soil beneath is left depressed. 



depression of the soil affords a means of watering the trees. 

 The soil immediately around the trunk is left at grade. See 

 Fig. 14. 



SUBIRRIGATION 



The installation of a system of subirrigation becomes 

 necessary to permit the watering of trees by sending the 

 water directly to the soil through tile pipes. This usually 

 consists of tile pipes about three inches in diameter, placed 

 with open joints at a depth of about a foot or a foot and a 

 half. A branch pipe, carried up to the surface of the ground, 

 furnishes an inlet to water delivered to the tree from a 

 water-cart or a hydrant hose. The drains are laid either in 

 the form of a rectangle surrounding the tree, or simply in a 

 straight line on one side of the tree, as shown in Figs. 15 

 and 16. In either case there is a branch pipe for the ad- 

 mission of the water. 



A cast-iron cap may be used to cover the opening at the 

 top of the branch pipe to prevent clogging with soil. To 

 guard against any tampering with the irrigation device, the 



