One of the most important lines of experiment, both 



for the Garden and all park and street planting, lies in 



^ „ .. the possibility of tree feeding, as 



Tree Feeding \ . ' . & '. 



a substitute lor sou deficiencies, 

 and of various soil treatments as a corrective for ab- 

 normal soil conditions. We know that under certain 

 circumstances beneficial results can be obtained by 

 tree feeding, but the time, method, and amount of 

 various possible soil applications are in need of careful 

 and protracted experimental study of a wide range of 

 species of shade and ornamental trees. 



Another tree problem of vital significance is that of 

 atmospheric pollution and its effect on tree life. It is 



, . _ „ „ known that minute amounts of 

 Atmospheric Pollution 



many gases which are natural 



by-products of the industrial and other activities of 

 great cities may have profound physiological and some- 

 times deleterious effects on plants. We share with our 

 own and all other city park authorities the duty of 

 investigating fully the matter of atmospheric pollution 

 in its relation to trees and other plant growth and must 

 reach practical solutions if we are to be able to safeguard 

 the natural beauties of parks under the conditions found 

 in modern commercially developed cities. We have 

 advanced far enough to know that the pollution of the 

 atmosphere by industrial establishments can frequent- 

 ly be controlled with financial advantage to their 

 owners, and it remains for us to show specifically just 

 what gases and what degrees of their concentration are 

 injurious to tree growth, and the measures that can be 

 applied most effectively for the prevention of their 

 occurrence in the air in dangerous quantities. 



The solving of the problems of the food, soil, water, 

 and atmospheric and climatic requirements of trees, 

 and of determining their rate of growth and longevity 



[12] 



