21 
TREES AS GOOD CITIZENS 
The worth of trees to a city is by no means confined to 
beauty. The city of fine shade trees is the City Healthful 
as well as the City Beautiful. In comfort, in health and in 
sanitation the shade tree is an important factor in civic 
welfare. Only a part of the benefit gained by man from 
shade trees is reckoned as by pleasure to the eye, and relief 
from the direct rays of the sun. Added to the welcome 
shelter is the cooling influence produced by the trees 
through their leaves; for trees transpire through their 
leaves in a way that has a pronounced influence on tem¬ 
perature. By absorbing moisture from the earth through 
their roots and releasing much of it into the air through 
their leaf-pores, the trees cool the air and freshen it. Enter 
the woods on a hot summer day, note that the temperature 
among the trees is several degrees lower than in the open. 
Wherever a shade tree spreads its leafy branches, this 
influence is constantly at work. 
By this process of evaporating and exhaling moisture, 
the trees not only reduce the temperature, but serve a 
further useful purpose in giving off oxygen required 
by man in the air he breathes; and, by drinking in the 
carbonic acid gas, perform a double function in purifying 
the air. 
Medical authorities recognize the value of trees in 
their influence on the health of a community. In the study 
of human illness, and particularly of the ailments of children 
in the crowded cities, doctors have found that trees do 
much toward reducing the death rate. Research has shown 
that one of the chief causes of sickness and death among 
the children of the congested districts is the stifling heat 
of midsummer days, intensified by reflection from heated 
pavements and sunbaked walls. On streets where shade 
trees are lacking, this reflected heat is given off night and 
day, to the severe discomfort and serious harm of people 
