STREET TREES. | 11 
be in active growth in the soil many forms of organic life that are in 
various ways preparing 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 products 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 
P14633HP 
Fic. 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 thesoil 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. 
