iv PREFACE. 



The preparation of the volume upon Physiological 

 Botany (Vegetable Histology and Physiology) is assigned 

 to the author's colleague, Professor GOODALE. 



The Introduction to Cryptogamous Botany, both structu- 

 ral and systematic, is assigned to his colleague, Professor 

 FARLOW. 



A fourth volume, a sketch of the Natural Orders of 

 Phsenogamous Plants, and of their special Morphology, 

 Classification, Distribution, Products, &c., will be needed 

 to complete the series : this the present author may 

 rather hope than expect himself to draw up. 



ASA GRAY. 



HERBARIUM OF HARVARD UNIVERSITY, 

 CAMBRIDGE April 10, 1879. 



*#* The numerals in parentheses, which are here and there introduced 

 into sentences or appended to them, are references to the numbered para- 

 graphs in which the topic is treated or the term explained. 



