Preface ix 



that I greatly appreciate. I am grateful also to Doctor Edgar 

 Anderson of the Missouri Botanical Garden for reading the page 

 proof and for an important suggestion. 



Many of the diagrams and illustrations are original, but in 

 any book of a general nature it is necessary to borrow from the 

 published works of others. I am indebted to Professor R. A. 

 Fisher, also to Messrs. Oliver and Boyd, Ltd., Edinburgh, for 

 permission to reprint Table III from their book Statistical 

 Methods for Research Workers. I also wish to express my ap- 

 preciation to the University of Chicago Press for permission to 

 use Figure 10, which had previously appeared in the Botanical 

 Gazette, to the American Naturalist for permission to borrow 

 Table 20, and to Scientific Agriculture for permission to repro- 

 duce Table 23. I wish also to express my sincerest thanks to 

 all the numerous journals which gave me permission to use their 

 material, to the many geneticists and cytologists who kindly 

 lent me original drawings or cuts, and to those who gave me 

 permission to redraw their published figures or to reproduce their 

 data. Individual acknowledgments have been made in the 

 legends of the figures or tables. 



Herbert Parked Riley 



University of Kentucky 



Lexington, Kentucky 



November, 1947 



