The Origin of Species 319 



have in that time changed sufficiently to make them 

 greatly different from their European prototypes. 

 If such changes have taken place, it would also be 

 interesting to know whether taken back to the old 

 home they would revert perfectly to the original 

 type. A critical study of this kind might very well 

 throw much light upon the mechanics of species 

 making. Bumpus made a study of the English 

 sparrow in the United States, and he found that 

 a perceptible modification had arisen in the bird 

 since it was introduced into the United States, some 

 thirty years earlier. Considering the readiness with 

 which plants vary, and the very much longer time 

 that many weeds have been naturalized in America, 

 it would be expected that a certain amount of 

 change had taken place. 



The conclusion to be drawn from a study of the 

 behavior of plants seems to be that both fluctuating 

 and discontinuous variations are important in 

 species forming. The effect of environment upon 

 organisms is unmistakable, and these effects are, 

 sometimes at least, transmissible to a greater or 

 less extent. This variation offers the handle for 

 natural selection to grasp, and the permanency of 

 any variation must depend upon natural selection. 



THE MUTATION THEORY 



The most notable theory of evolution that has ap- 

 peared of late, is the Mutation Theory of De Vries. 



