A City's Need for Trees.--The city of Paris, well known as one of the most beautiful of European capitals, spends over $100,000 annually in caring for and replacing some of the 90,000 trees owned by the city. All over the United States the city governments are beginning to realize what European cities have long known, that trees are of great value to a city. They are now following the example of European cities by planting trees and by protecting the trees after they are planted. Thousands of city trees are annually killed by horses which gnaw the bark. This may be prevented by proper protection of the trunk by means of screens or wire guards. Chicago has appointed a city forester, who has given the following excellent reasons why trees should be planted in the city:-- (1) Trees are beautiful in form and color, inspiring a constant appreciation of nature. (2) Trees enhance the beauty of architecture. (3) Trees create sentiment, love of country, state, city, and home. (4) Trees have an educational influence upon citizens of all ages, especially children. (5) Trees encourage outdoor life. (6) Trees purify the air. (7) Trees cool the air in summer and radiate warmth in winter. (8) Trees improve climate and conserve soil and moisture. (9) Trees furnish resting places and shelter for birds. (10) Trees increase the value of real estate. (11) Trees protect the pavement from the heat of the sun. (12) Trees counteract adverse conditions of city life. Let us all try to make Arbor Day what it should be, a day for caring for and planting trees, for thus we may preserve this most important heritage of our nation. REFERENCE BOOKS ELEMENTARY Hunter, _Laboratory Problems in Civic Biology_. American Book Company. Mayne and Hatch, _High School Agriculture_. American Book Company. Murrill, _Shade Trees_, Bul. 205, Cornell University Agricultural Experiment Station. Pinchot, _A Primer of Forestry_, Division of Forestry, U. S. Department of Agriculture. ADVANCED Apgar, _Trees of the United States_, Chaps. II, V, VI. American Book Company. Coulter, Barnes, and Cowles, _A Textbook of Botany_, Part I and Vol. II. American Book Company. Goebel, _Organography of Plants_, Part V. Clarendon Press. Strasburger, Noll, Schenck, and Karston, _A Textbook of Botany_. The Macmillan Company. Ward, _Timber and Some of its Diseases_. The Macmillan Company. Yearbook, U. S. Department of Agriculture, Division of Forestry, Buls. 7, 10, 13, 16, 17, 18, 20, 26, 27. X. THE ECONOMIC RELATION OF GREEN PLANTS TO MAN _Problems.--How green plants are useful to man._ _(a) As food._ _(b) For clothing._ _(c) Other uses._ _How green plants are harmful to man._ SUGGESTED LABORATORY WORK