Grateful acknowledgment is hereby made to Miss Sarah Phelps, who has done most of the inking in and given life to the author’s pencil-drawings; to Mr. J. H. Ehlers for his valuable assistance in the preparation of many of the drawings and in the collection of working material; to Prof. Henri Hus, who has read all of the proof and who has at various times rendered valuable assistance; to Prof. F. C. Newcombe and to Prof. Ernst Bessey for the loan of sheets, from the herbariums of the University of Michigan and Michigan Agricultural College; and especially to Prof. Geo. P. Burns in whose inspiration this bulletin had its inception and under whose direction the work has progressed to completion. Chas. H. Otis.
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