PREFACE. xiii 
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. Iam 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. [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 sucha 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. Ihope, 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 fiora, 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 
University of Minnesota 
December 24, 1892 
