PREFACE vii 
the sequence used by the teacher. For example, work on 
leaves, stems, roots, and seeds may come in any order, and 
may well differ according to the availability of material or the 
conviction of the teacher. It so happens that the book begins 
with leaves, but those teachers who prefer to begin with seeds 
should do so. 
In the matter of illustrations, there have been many im- 
provements, eliminations, and additions. All of this work 
has been done or directed by my assistant, Dr. W. J. G. Land, 
whose skill in photography has been made use of freely and 
whose coéperation has added much to the value of the book. 
Unless otherwise credited, all illustrations have been prepared 
for this volume or those previously mentioned. 
Joun M. Coutrer. 
Tue UNIVERSITY oF CHICAGO, 
September, 1908. 
