ULLRICH] SOME REASONS FOR THE STUDY OF TREES 21 



Similarlv, if the students in iiattire-study make observations of 

 the injun' to local trees b}- the wind, ice, snow, extreme heat or 

 cold, excessiv^e drought or moisture, insects, and fimgi; of the 

 formation of humus by the decomposition of the fallen leaves; and 

 of the soil binding qualities of the extensive root systems; they 

 receive the best possible preparation for intelligent cooperation 

 with local, state, and national organizations for the preservation of 

 our forests, by checking the agencies operative in forest destruction. 

 Through this type of instruction, as a part of the study of local 

 trees, the articles in the daily press, in the btilletins issued by the 

 conservation commissions, and other pubHcations on the import- 

 ance of forests in the prevention of destructive erosion and floods, 

 and in the establishment of permanent irrigation projects in certain 

 localities, become meaningful. Likewise, the discussions of 

 forestry' benefits in the classroom or from the public fonmi will not 

 fall on barren soil. 



Another economic motive for the study of trees about us is the 

 value of trees in the maintenance of the health of the community. 

 It is common experience, after work in the open under the hot rays 

 of the sun, to receive new vigor and energA- from rest in the cooling 

 shade of some tree or trees. It has been estimated that the annual 

 loss in the United States from unnecessary- illness, medical attend- 

 ance and loss of wages amounts to nearly $1,000,000,000, about 

 two times the total expenditure for public education in this country-. 

 Without trees, the most conspicuous portion of the vegetation, at 

 least, in the villages and smaller cities, there is reason to believe 

 the loss from ill-health might be greater than it is. If it is accepted 

 without question, that the physical well-being of the people of a 

 community is improved through the shade of trees, a study of one 

 of the life processes of trees may suggest some other relation of 

 trees to public health. Assail students of plants know, the 

 chlorophyll in the leaves and^other green parts of the tree, "con- 

 jures with the s\mbeams" in the imion of the water from the soil, 

 and the carbon dioxide from the air, into some form of carbo- 

 hydrate. In this process oxygen, an element absolutely essential 

 for the sustenance of life in either plant or animal, is set free into 

 the air. An attempt at a mathematical statement of the amount 

 of benefit in terms of health, from the introduction of oxygen into 

 the air by the green cells of trees would be foolhardy, because as 

 yet no method for computation has been devised. As a cumulative 



