PREFACE 



A FEW years ago I published a short sketch of 

 Mendel's discovery in heredity, and of some of the 

 recent experiments which had arisen from it. Since 

 then progress in these studies has been rapid, and the 

 present account, though bearing the same title, has been 

 completely rewritten. A number of illustrations have 

 been added, and here I may acknowledge my indebted- 

 ness to Miss Wheldale for the two coloured plates of 

 sweet peas, to the Hon. Walter Rothschild for the but- 

 terflies figured on Plate VI., to Professor Wood for 

 photographs of sheep, and to Dr. Drinkwater for the 

 figures of human hands. To my former publishers also, 

 Messrs. Bowes and Bowes, I wish to express my thanks 

 for the courtesy with which they acquiesced in my 

 desire that the present edition should be published 

 elsewhere. 



As the book is intended to appeal to a wide audience, 

 I have not attempted to give more experimental in- 

 stances than were necessary to illustrate the story, nor 

 have I burdened it with bibliographical reference. The 

 reader who desires further information may be referred 

 to Mr. Bateson's indispensable volume on Mendel's 



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