PREFACE 



In sending out the present volume as an addition to the 

 literature of evolutionary science, the writer feels that a few 

 words of personal explanation may be appropriate. 



As a university student he was deeply impressed, during 

 the epochal period from 1875 to 1882, by the varied — often 

 conflicting — views on evolution presented by his teachers. So 

 he early formed a resolve to investigate quietly, but as ex- 

 tensiA^ely as possible, the problems presented by organisms 

 from the simplest types up to man himself. Later as a teacher 

 and investigator of biological and specially of botanical prob- 

 lems, during a period of well nigh forty years, he has had con- 

 siderable, and in some respects exceptional, opportunities for 

 becoming acquainted with organisms over extensive fields of 

 the Old and New World; for studying the structure and be- 

 havior of these in laboratory, in experimental grounds, and in 

 cultural houses; as well as for quiet study of biological litera- 

 ture personally and in conjunction with his graduate students. 



Though a student and teacher of zoological as well as botan- 

 ical science for about ten years of his earlier academic career, 

 he would in many ways have preferred to confine attention to 

 the latter science, that has been his chosen field for specialized 

 investigation. But questions constantly presented themselves 

 from the side of plant life, that seemed to demand continuous 

 study and solution from the animal side as well. If one such 

 case may be cited here, reference might be made to the past 

 and present geographical distribution of plants as eminently 

 favoring the view that these originated over fresh- water areas, 

 and only secondarily spread into the sea. As the truth of 

 this became increasingly evident, the writer was confronted by 

 the universally accepted though opposing view of zoologists 

 that animal life originated in the sea, and thence spread land- 

 ward. Here then was a seeming l)iological anomaly that 

 called for investigation. The results of such are shortly i)re- 



