Apgar, _Trees of the United States_, Chaps. II, V, VI.
American Book Company.
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Vol. I.
American Book Company.
Duggar, _Plant Physiology_. The Macmillan Company.
Ganong, _The Teaching Botanist_. The Macmillan Company.
Goebel, _Organography of Plants_, Part V. Clarendon Press.
Goodale, _Physiological Botany_. American Book Company.
Gray, _Structural Botany_, Chap. V. American Book Company.
Kerner-Oliver, _Natural History of Plants_. Henry Holt and
Company.
Strasburger, Noll, Schenck, and Karston, _A Textbook of
Botany_. The Macmillan Company.
Ward, _The Oak_. D. Appleton and Company.
Yearbook, U. S. Department of Agriculture, 1894, 1895,
1898-1910.