STREET TREES. 



IX 



be in active growth in. the soil many forms of organic life that are in 

 various ways ])rcparing the material in the soil for the use of the 

 larger plants. Not only must these things be present, but others 

 that are deleterious must be absent, whether the substance is hurtful 

 in itself or whether it is an excess of one that is otherwise beneficial. 



Above the soil three things must be present — air, sunlight, and 

 moisture — and, as in the soil, harmful things must be absent in order 

 to have success. Among the deleterious substances are sulphur and 

 other fumes and soot and other })roducts from incomplete combustion. 



Some of the more obvious things with which a city tree has to 

 contend are: Water-tight pavements, both on the sidewalk and 



PI 4533 HP 



Fig. 9.— The irregularity in the size of the trees shown is due to a part of the first planting having been 

 killed by illuminating gas from defective pipes. Norway maples as seen in Washington, D. C, in 

 late winter. 



street, that prevent the admission of air and water; the removal of 

 the topsoil in street grading, thus forcing the tree to exist on the 

 good soil provided in the hole; careless digging near the tree for gas, 

 water, and electric service, and especially for the placing of curb- 

 stones ; the saturation of the soil with illuminating or sewer gas from 

 defective pipes (fig. 9) ; the pouring of salt water from ice-cream 

 freezers into gutters, where it may find its way into the soil near tree 

 roots; the gnawing of the trunks by horses; and the cutting of the 

 tops by linemen and tree trimmers. 



Because of the uncongenial conditions for the growth of trees on 

 city streets comparatively few kinds are satisfactory for such use. 



