240 



Biology in America 



pie cited by Darwin. Still other instances are those of horn- 

 less cattle, hairless dogs, bob-tailed cats, web-footed chickens 

 and extra-fingered men. These however are exceptional 

 cases; the great mass of mutations, those mainly productive 

 of evolution, are of the minor sort, appreciable only by care- 

 ful measurement and statistical analysis. 



The presentation of the mutation theory in its present form 

 we owe mainly to the Dutch botanist, DeVries. A brief 

 resume of the latter 's work will bring the subject fairly be- 



An example of 



A KUMPLESS FOWL 

 mil' at, on. From Davenport, 



Inheritance in 



PouLry, " Carnegie Institution, Publication No. 52. 



fore us. Over thirty years ago DeVries found certain well- 

 marked varieties of the evening primrose, a native of Amer- 

 ica, which had been introduced into Europe and was grow- 

 ing as a weed around the city of Amsterdam. Specimens of 

 these varieties and of the parent species were transplanted 

 in his garden and bred for many years including eight gen- 

 erations, during which time he discovered and recorded over 

 800 variations from the parent type, whose possessors bred 

 true to themselves. By selection of these variations he was 

 able to produce a large number of distinct types of prim- 

 rose which he called "elementary species," 



