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tures, its rivers, lakes, peaks and cliffs. The detail must be worked out 

 by those who come after. In the case of Darwin the map remains sub- 

 stantially as it was, although many have worked at the various details 

 with which the modern chart is filling up. The discovery of the micro- 

 scope has enabled us to frame a rational theory of heredity and to under- 

 stand with some degree of certainty the physical basis of the functions 

 of inheritance. The morphology of animals has been very fruitfully studied 

 by many men. Many others have developed the history of past life on the 

 earth, and we would have to have a theory of evolution to account for 

 this, if Darwin had not furnished one already. 



The three men most famous since Darwin are these : Wagner, Weiss- 

 maun and Mendel. Mendel died before Darwin wrote and his work on the 

 "Heredity of Peas" was forgotten until after Darwin's time, but has be- 

 come a very important factor in our experimental studies of living forms 

 in relation to inheritance. Wagner was the first one to lay adequate stress 

 on the idea of isolation as a species-forming influence. His weakness was 

 that he rejected selection as an element, assigning to isolation the impos- 

 sible task of accounting for all the external phenomena in the origin of 

 species. To Weismann we owe more than to any one else our present 

 knowledge of heredity. 



Theories of less importance are Eimer's orthogenesis, which has a 

 good deal behind it, and which we shall probably accept if some genius 

 will arise to tell us what it means. It rests on the fact that we have many 

 long series of animals which seem to have progressively varied as time 

 went on. 



The study of the mutations of the evening primrose by De Vries has 

 given many hints as to possibilities in plant breeding. I do not believe that 

 the theory that species are mainly or largely formed by sudden mutations 

 will survive the present generation of De Vries' followers, but the impulse 

 given to experimental study of plants will long continue. 



More than thirty years ago I used these words in Indianapolis : 



"Darwin lies in Westminster Abbey, by the side of Isaac Newton, one 

 of the noble men of the past whose life had made his own life possible. 

 Of all who have written or spoken, by none has an unkind word been said. 

 His was a gentle, patient and reverent spirit, and by his death has not 

 only science, bid our conception of Christ, been advanced and ennobled." 



