vi PREFACE 



In the seventeenth chapter are summarized the important 

 general principles derived from the investigation of related living 

 and extinct organisms. The beginning of the studies leading 

 to the formulation of these anatomical canons stands largely to 

 the credit of French and English paleobotanists. Since they 

 have worked mainly with Paleozoic types, their activities have 

 been preponderantly in the direction of comparisons between the 

 organization of the earlier cryptogams and gymnosperms and 

 their still living survivors. It has been in some measure the 

 good fortune of American anatomists to continue the lines of 

 investigation thus begun and to extend them to the study of 

 Mesozoic and still living gymnosperms. The extremely harmoni- 

 ous conclusions resulting from the anatomical comparison of both 

 Paleozoic and Mesozoic forms with their surviving descendants 

 have justified the extension of the same principles to the evolu- 

 tionary investigation of other woody plants (particularly to the 

 angiosperms), concerning the geological past of which we are still 

 ignorant. The canons formulated in chapter xvii have as a conse- 

 quence been regarded of such importance that any conclusions not 

 in harmony with them have ordinarily not been considered in the 

 following pages unless they have held the ground for many years 

 or are at the present time advocated by anatomists of great emi- 

 nence: On account of the large field covered in the present neces- 

 sarily elementary work, this procedure has been regarded as 

 essential, and it is hoped that, with the explanation offered, it 

 will not appear to the reader too dogmatic. 



The author has been fortunate in utilizing the services of his 

 students in the preparation and illustration of this volume. He 

 is particularly indebted to Mr. R. E. Torrey for his skilful and 

 artistic execution of a large number of the figures. Help in 

 this respect has also been supplied by Mr. R. C. Staebner and 

 Mr. Charles Drechsler. Miss Ruth Cole has rendered invaluable 

 aid in the onerous task of preparing the text and reading the 

 proof. Miss Edith S. Whitaker has also assisted in the prepa- 

 ration of the index. 



To Professor M. A. Chrysler, of the University of Maine, the 

 author owes illustrations of secondary growth in monocotyledons, 



