PREFACE 



In view of the decidedly unsettled state of nomenclature 

 at the present time, it has seemed best to maintain a some- 

 what conservative attitude in this matter, and this will ex- 

 plain the retention of some familiar names, which perhaps 

 are not in accord with a strict law of priority. 



The author is especially indebted to Professor E. C. 

 Jefifrey and to Dr. W. R. Shaw, for valuable preparations 

 which were of great assistance in the preparation of the 

 chapters on the Ferns. Thanks are also due one of my 

 students, Mr. H. B. Humphrey, for the preparation of the 

 drawings for figures 43, 44 and 47. 



The author also would express his thanks to Professor 

 D. S. Johnson of Johns Hopkins University for kindly re- 

 vising a portion of the bibliography, and to Professor G. 

 J. Peirce of Stanford University for valuable assistance in 

 reading part of the proof. 



DOUGLAS HOUGHTON CAMPBELL. 



Stanford University, 

 April, 1 905. 



