iv. PREFACE 
In deference to the wishes of many teachers, chapters on 
Plant Breeding, on Useful Plants, and on Timber and Forestry 
have been added. This matter may be used as a basis on which 
to build further reading for brief essays. Or it may suggest 
elementary investigations into the horticulture, the agricul- 
ture, or the forest conditions of the student’s own neighbor- 
hood. The study of useful plants and their products may be 
taken up from Chapter xxx as the topics suggest themselves 
in earlier portions of the text, i.e., seeds as food and medicine 
in connection with Chapter 11, and so on. 
The author wishes to thank Dr. A. A. Lawson, now of the 
University of Glasgow, Scotland, who read the manuscript of 
Chapters xx1I-xxvit, for many valuable suggestions. Thanks 
are also due to Professor D. P. Penhallow of McGill Uni- 
versity, Montreal, for suggestions on Chapter xxv111, and to 
Dr. H. von Schrenk of St. Louis for aid on the chapter on 
Forestry. 
Grateful acknowledgments are due for the use of illustra- 
tions copied for various figures as follows: D. H. Campbell, 
208, 215; H. W. Conn, 170, 171, 175; W. G. Farlow, 160; 
A. E. Frye, 232, 234; C. F. Hodge, 225; A. D. Hopkins, 237; 
D. 8. Jordan, 223; F. Roth, 236; J. H. Schaffner, 208; H. J. 
Webber, 224. Special mention should be made of the unpub- 
lished yucca drawing by Mrs. Grace Johnson Vieh, loaned by 
Professor William Trelease and used for Fig. 132. Some of the 
cuts above mentioned have been re-drawn, others are printed 
from the original wood engravings or zinc etchings. 
A large proportion of the illustrations in Chapters xx1v— 
xxx have been re-drawn for the present book from the most 
authoritative sources by E. N. Fischer, F. 8. Mathews, and 
C. H. L. Gebfert. 
J. Y.B, 
CAMBRIDGE, MassaCHUSETTS 
