PREFACE TO THE FOURTH EDITION 
been lengthened by 20 pages and several illustrations on Carniv- 
orous plants. 
Every part of the work has been carefully revised and brought 
uptodate. As in former editions, the index has been so planned 
as to make the information contained in this book readily 
accessible. 
To the authors from whom cuts were borrowed, the writer’s 
thanks are due. 
