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- 

 pling 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, 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 Chapter XXXVI, and 

 to whose stimulating comments is due much of whatever 

 value that chapter 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. 



