PREFACE. 



The great importance of the eusporangiate ferns as the nearest existing rela- 

 tives of the Paleozoic ancestors of the higher types of flowering plants invests 

 them with an especial interest for the student of plant evolution; and no apology 

 is necessary for presenting at length a summary of our present knowledge of the 

 structure and development of these important plants. 



For more than twenty years the writer has been much interested in the study 

 of the Eusporangiatae and during this time has published a number of works deal- 

 ing with them. He has had rather unusual opportunities for collecting these forms, 

 and an extensive and representative collection of materials comprising a good many 

 species has been accumulated, so that the time seemed ripe for a comparative study 

 of the group, for the purpose of determining, as far as might be, the relationships 

 existing between the different genera, as well as for throwing some light upon the 

 question of their position in the great series of ferns. 



The present memoir is an attempt to present the results of these studies, based 

 mainly upon the writer's own materials, but supplemented by a careful study of 

 the work of other investigators who have described the structure and development 

 of the Eusporangiatae. 



The writer's grateful acknowledgments are due to a number of colleagues who 

 have rendered assistance in various ways. Especially is he indebted to Prof. E. C. 

 Jeffrey, through whose kindness a large number of admirably preserved prothallia 

 and young plants of Botrychium virgmianum were sent the writer, and in addition 

 a number of valuable slides of the same. Without this material the work on Bo- 

 trychium would have been very incomplete. 



To my colleague in Stanford University, Prof. L. L. Burlingame, thanks are 

 due for valuable assistance in the preparation of the photographic plates, as well as 

 for the use of a number of important slides of Ophioglossum and Helminthostachys. 



To Prof. J. C. Willis, of the Botanic Gardens at Peradeniya, the writer would 

 express his appreciation of many kindnesses and assistance in collecting during his 

 stay in Ceylon. 



It was the good fortune of the writer to enjoy the unequaled facilities for 

 collecting material offered by the great gardens at Buitenzorg and Tjibodas in Java, 

 where, through the interest and courtesy of the distinguished director, Professor 

 M. Treub, whose recent death was such an irreparable loss to science, means were 

 afforded for securing the most valuable materials used in the preparation of the 

 present work. 



Douglas Houghton Campbell. 



Stanford University, April, 1910. 



