PREFACE 



It may be, of course, that we have over-siniphfied our story. It 

 may be that, in seeing heredity as the outcome, as well as the material, 

 of adaptive and evolutionary change, and in assuming in it a unity 

 of principle which applies also to development and infection in all 

 plants and animals (even in ourselves), we have travelled too far 

 and too fast. We do not hope to satisfy the critic who prefers the 

 small, the single, and the secluded, department. But we do hope that 

 many, whether wise veterans or innocent enthusiasts, who read this 

 book, will share some of the delight we have had in writing it. 



C. D. D. 



K. M. 

 John Innes Horticultural Institution, Merton 

 December 1947 



ACKNOWLEDGEMENT 



We are indebted to the various authors and publishers of periodicals 

 and books named in the References to each chapter for the use of their 

 figures in the text. 



Note on Frontispiece 



It has been pointed out to us, by Professor R. A. Fisher, that the figures on 

 this page of Mendel's notes suggest factor interaction. Thus the ratio of 343 : 92 : 166 

 in the middle of the page suggests the 9:3:4 ratio characteristic of an F^ segre- 

 gating for two genes related in action by recessive cpistasy (see Fig. 38 on page 

 156). This is all the more likely as the class of 166 is recorded near the top of the 

 page as "weiss" and denoted as W. If this inference of epistasy is correct, the results 

 were perhaps from beans rather than from peas. Mendel mentions work with 

 beans (including the species cross Phaseolus vulgaris X Ph. timltifiorus) in his paper, 

 but gives httle detail of the results, which he evidently found difficult to interpret. 

 He makes no mention of any epistatic colour relations in his peas and the notion of 

 cpistasy was not introduced until 1907. 



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