vi PREFACE. 



The volume upon Physiological Botany (Vegetable His- 

 tology and Physiology) has been prepared by the writer's 

 colleague, Professor Goodale. 



The Introduction to Cryptbgamous Botany, both struc- 

 tural and systematic, is assigned to the writer's colleague. 

 Professor Faelow. 



A fourth volume, a sketch of the Natural Orders of 



Phsenogamous Plants, and of their special Morphology, 



Classification, Distribution, Products, etc., wiU be needed 



to complete the series : this the writer may rather hope 



than expect himself to draw up. 



ASA GRAY 



Hereakidm op Hakvard University, 

 Camgridgx. 



