PREFACE TO THE SECOND EDITION 



In getting ready the second edition it became evident that a 

 chapter on reproduction should be added. Because of its 

 promise in helping to solve the problem of evolution and its great 

 importance for plant and animal breeding the subject of repro- 

 duction and heredity has come to the forefront of biological 

 research; and especially under the great light that has shone from 

 Mendel's laws has eager investigation been directed toward the 

 details of cell behavior in reproduction. 



It cannot yet be said that these investigations have arrived at 

 undisputed achievement, but their results, however tentative, 

 are so suggestive of important possibilities as to justify their 

 survey in a text-book for students in colleges and agricultural 

 schools. 



Necessarily that part of the chapter on reproduction dealing 

 with an interpretation of observed nuclear behavior that has 

 frequently been suggested in current literature is a fit subject 

 for critical examination and debate, and as such it will serve its- 

 purpose of marking a present-day view arising from a con- 

 templation of observed facts of structure and behavior. 



The theory of pangenes and unit characters may or may not 

 stand as our knowledge advances, but it is serving the purpose 

 in biology to-day that the atomic theory has so long and honorably 

 fulfilled in chemistry. 



Of great aid to me in the preparation of Chapter XIII have 

 been Coulter and Chamberlain's Morphology of Angiosperms, 

 Mottier's Fecundation in Plants, Mendel's Principles of Heredity, 

 by W. Bateson, Strasburger's Die StofHichen Grundlagen der 

 Vererbung, Lotsy's Vorlesungen iiber Deszendenztheorien, 

 de Vfies's Die Mutationstheorie, Species and Varieties, and 



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