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.