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tematic way more cheaply and efficiently than would be 
possible by individual effort. The work can be done at 
less cost, because the trees and all other materials are 
purchased in large quantities at low wholesale rates. The 
work can be done more efficiently, because done by trained 
experts, devoting their entire time to the planting and care 
of street trees. 
Conditions Necessary for Successful Tree Growth. 
Handsome street trees will grow only where the roots 
have air, water and good soil. Trees may live for a time 
without one or more of these necessities, but growth will 
be poor and the life of the tree short. In some streets, 
particularly in the suburbs, fertile top-soil exists under 
tne sidewalks, but more often it does not, the ground 
being too sterile to support even a blade of grass. Where 
bad soil exists, a large hole must be dug and the poor 
material replaced with one or two loads of good loam. 
To allow water and air to reach the roots concrete pave- 
ments must be kept several feet away from the base of 
the tree. A continuous grass or gravel planting strip 
from three to six feet wide is the ideal arrangement for 
street trees and should be provided where the best trees 
are desired. 
Kinds of Trees Suitable. Only a few kinds of trees 
will grow satisfactorily in our streets. The Carolina poplar 
and silver maple, the most frequently planted trees in 
Philadelphia, are almost entirely unsuited to the purpose. 
They are Loth short-lived, weedy trees, which require con- 
stant topping to prevent them from becoming dangerous, 
and their soft, brittle wood decays readily. The roots in- 
vade and clog drain pipes and heave sidewalks. 
Good trees for street planting are the oriental plane, 
pin oak, gingko and ^N^orway maple. The plane will thrive, 
where few other trees grow, and it may be pruned into any 
