THE PLANTING OF STREET-TREES 101 



selection and planting of a tree, if the water table is so low 

 that the roots are always moist and there is no access of air 

 to it, the tree will die. Proper subsoil drainage frequently 

 presents one of the most insuperable problems in tree- 

 planting. If the soil is of an impervious nature, but limited 

 in thickness, it should be either dug through to the more 

 pervious soil or a drain carried to the lower stratum. A 

 drain connecting with a street-sewer will also serve to carry 

 off water that is likely to collect at the roots. Such drains 

 should be placed at a depth of from three and one-half to 

 four feet 



