324 



COOK 



" hereditary mechanism." The figure of developmental progress 

 under the kinetic theory is that of the advance of a huge and 

 intricate network or trestle, built and supported by the inter- 

 grafting of the lines of descent throughout the species. Envi- 

 ronmental obstacles can compel the progressive advance of this 

 specific structure to be accomplished by many lateral bendings, 

 but these deviations and displacements need no longer be mis- 

 taken for examples of normal evolutionary motion. That indi- 

 vidual organisms can step aside, or even fall out of the ranks, 

 proves, at the most, only that such transverse motions are pos- 

 sible ; it does not show that they represent the method or the 

 conditions by which the constructive evolutions of natural species 

 go forward. The environmental reactions and mutations are 

 made suddenly and can be readily demonstrated to our impa- 

 tient eyes, but the coherent advance of the whole specific net- 

 work has to be inferred from the relations of species as we find 

 them in nature. 



Some are inclined to distrust the results of the cosmic labora 

 tory and to prefer to explain evolution by the lateral diversions 

 which can be demonstrated in their own experimental cages 

 and gardens. After keeping Lamarck's evening primroses in 

 his garden for eighteen years without detecting any change, 

 Professor De Vries has concluded that the species is constant 

 and stationary and that further evolution is accomplished only 

 by mutative variations, like those which appeared during this 

 interval. 



"There is neither a gradual modification nor a common 

 change of all the individuals. On the contrary, the main 

 group remains wholly unaffected by the production of new 

 species. After eighteen years it is absolutely the same as at 

 the beginning, and even the same as is found elsewhere in 

 localities where no mutability has been observed. It neither 

 disappears nor dies out, nor is it ever diminished or changed in 

 the slightest degree. 



..." My evening primrose, however, produces in the same 

 locality, and at the same time, from the same group of plants, 

 quite a number of new forms, diverging from their prototype 

 in different directions. 



