X PREFACE 



command of botanical science in general, than can be given him 

 merely through a series of lectures and recitations. Anyone 

 who has mastered the facts presented in the text and who has 

 at his command a reasonably broad body of experience, ought 

 to be able, through the exercise of a little thought, to prepare 

 satisfactory answers for all of them. "Thought questions" 

 are by no means new in botanical pedagogy, but it is believed 

 that no previous text has employed them to quite such an extent 

 as does the present one. It is hoped that their inclusion here 

 may encourage a method of class-room procedure more satis- 

 factory than the common but somewhat outworn practice where- 

 in a monopoly of thinking and talking is enjoyed by the 

 instructor, and the student is chiefly required to memorize a 

 series of what often seem to him to be unrelated facts. The 

 "Reference Problems" are designed to send the student occasion- 

 ally to other sources of information than his textbook, and thus 

 to broaden his point of view and dispel from his mind the com- 

 fortable assurance that any particular authority may be infallible. 



To all those who have been of assistance in the preparation of 

 the book the author desires to express his sincere thanks. Many 

 of his colleagues have contributed helpful suggestions and 

 information in matters relating to their special fields, and to 

 Professor G. S. Torrey is he especially indebted for advice and 

 assistance during the course of the work. Professor Torrey and 

 Dr. L. C. Dunn have been good enough to read and criticize 

 portions of the manuscript. A. I. Weinstein has been helpful 

 in many ways. Professor M. L. Fernald of the Gray Herbarium 

 kindly supplied the data used in Figs. 131, 132 and 133. To 

 Professor B. M. Davis of the University of Michigan and Pro- 

 fessor J. W. Harshberger of the University of Pennsylvania the 

 author is under obligation for their courtesy in providing material 

 and facilities for the preparation of a number of the figures. He 

 is also much indebted to his wife for frequent assistance during 

 the preparation of text and illustrations. 



The great majority of the illustrations are original. They are 

 the work of several individuals, to whom the author is grateful 

 for hearty cooperation. Mrs. Grace Griffin Hosking is responsi- 

 ble for Figs. 21, 22, 26, 66, 81, 99, 135, 136, 141, 142, 144, 145, 

 146, 147, 149, 151, 152, 153, 157, 158, 159, 160, 161, 174, 181, 184, 

 185, 187, 188, 189, 196, and 216; H. C. Creutzburg for Figs. 20, 

 45, 47, 96, 156, 162, 166, 167, 169, 170, 175, 177, 178, 180, 182, 



