PREFACE XV 
value. Special acknowledgment is made of Dr. Olive's 
interest and assistance in supervising the preparation of 
the drawing for Fig. 198, on the wheat rust, and for sup- 
plying the microscopical preparations from which a 
number of illustrations have been made, as indicated in 
the legends. 
A similar valuable service was rendered by Dr. O. E. 
White in reading and discussing the manuscript and 
proof of Chapters XXXII-XXXVIII, and in reading 
all of the galley proof and part of the page proof; and 
by Mr. Norman Taylor, in reading manuscript and proof 
of Chapters XXVII-XXX. 
The author is indebted to Prof. E. C. Jeffrey, of Harvard 
University, and Prof. E. W. Berry j of the Johns Hopkins 
University, for suggestions and criticisms in connection 
with the genealogical trees (Figs. 433 and 434), and 
especially to Prof. G. R. Wieland, of Yale University, who 
critically read the manuscript of Chapters XXXVII and 
XXXVIII, and to whose stimulating comments is due 
much of whatever value these chapters may possess. 
For any imperfections and inaccuracies, of whatever 
sort, in the subject matter, the author alone is responsible. 
C. STUART GAGER. 
BROOKLYN BOTANIC GARDEN. 
July 19, 1916. 
