PREFACE. Xlll 



phyta. An extended discussion of the point will not be proper 

 here, but it may be noted in passing that the proposition that 

 the pro-embryo of Chara is really homologous with a sporo- 

 phytic plant is not altogether indefensible. 



Acknowledgements not already made in the introductory 

 chapter may here find an appropriate place. To very many L 

 am under grateful obligation for assistance and encouragement. 

 I may name most particularly Dean C. W. Hall, of the Univer- 

 sity of Minnesota; Dr. N. L. Britton, of Columbia College; 

 Prof. E. L. Greene, of the University of California, and Dr. 

 C. E. Bessey, of the University of Nebraska. Each one of 

 these has aided me and I take pleasure in assuring them of my 

 sincere gratitude and regard. I am also indebted to Maud R. 

 MacMillan, my wife, for no little help in the proof-reading and 

 indexing-work, and to my sister. Bertha McMillan, for similar 

 kindly offices. I extend my thanks to them. 



The general plan of this volume will be recognised by my 

 professional co-workers as somewhat new, or at least untried. 

 They will doubtless appreciate without any further statements 

 on my part, the many difficulties that confront one who attempts 

 to follow such a plan. I trust they will also bear in mind that 

 the writer is Keenly aware of many defects in his work, and 

 doubts not that there are others which have escaped his atten- 

 tention. Oversights, errors and positive blunders are scarcely 

 to be avoided in any work that is made up of such a mass of 

 detail as in the case in hand. I hope, however, that these errors 

 have been reduced to a minimum, and that such as exist, in 

 spite of what I trust has been a due degree of watchfulness, 

 will not mislead anyone who may use this book. In spite of 

 the onus that to a certain degree rests upon the compiler of a 

 local tiora, I believe that even in such a humble department of 

 botanical science there is opportunity for useful study. Where 

 the present work may have failed, others, it may be hoped, will 

 succeed, and, if directly or indirectly the writer has contributed 

 a little to the development of our knowledge of the plant popu- 

 lation of the continent, he will feel well repaid for labors which 

 have at times been both arduous and confining. 



Conway MacMillan 

 Universifjj of Minnesota 

 December 24, J 892 



