MUTATION 309 



While Darwin was well acquainted with those dis- 

 continuous variations, he disregarded them entirely in 

 formulating his theory; he considered them as an in- 

 significant factor in comparison with continuous indi- 

 vidual variations which are so frequent and so general. 

 From Darwin's time, however, to the present day, 

 many naturalists have endeavoured to make discon- 

 tinuous variation the basis of evolution theories. In 

 1864 Kollicker, in 1877 Dall, and more recently, in 

 1901, Korshinsky held the belief that these saltations, 

 these variations without transitional forms (a phe- 

 nomenon designated as heterogenesis) were responsi- 

 ble, to the exclusion of infinitesimal individual fluctua- 

 tions, for every transformation of species. 



This theory, supported by a large number of exper- 

 iments, was developed into a real system by the 

 Dutch botanist De Vries, who designated it as the 

 Theory of Mutation. It is winning recognition from 

 a constantly increasing number of biologists. Among 

 De Vries' predecessors we can only name one whose 

 views are worth while recording. It was Korshinsky 

 according to whom the evolution of species is due to 

 the sudden appearance of certain modifications which 

 are transmitted to the offspring, especially in cases of 

 reproduction by nodes, layers, etc. These modifica- 

 tions originate in the germinal cells, and as far as 

 the individual is concerned, they are independent of 

 the external environment; the latter, however, is an 



