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THE AMERICAN NATURALIST [Vol. XLIII 



to be required in his own theory to meet the then 

 dawning truth. De Vries declares that his own field re- 

 searches and testing of native plants are based "on the 

 hypothesis of unit-characters as deduced from Darwin's 

 Pangenesis," which conception, De Vries points out, "led 

 to the expectation of two different kinds of variability, 

 one slow and one sudden." 29 



But the main point I wish to dwell upon at present is 

 that Darwin recognized, at least dimly, a kind of varia- 

 bility the results of which were essentially different from 

 the "individual" or "indefinite" variations, which mis- 

 takenly seemed to him alone capable of being acted upon 

 by selection. He was sorely puzzled by what he saw 

 and realized in this direction, for he had spent more than 

 twenty years of intense thought in elaborating his theory 

 that new species were evolved from older ones by the 

 gradual building up of new characters from extremely 

 small differences, and he feared that the admission of 

 saltation in any form meant the undermining of the foun- 

 dations he had labored so hard to construct. He had once 



galls, and certain monstrosities, which cannot lie accounted for by 

 reversion, cohesion, &c., and sudden strongly-marked deviations of 

 structure, such as the appearance of a moss-rose on a common rose, 

 we must admit that the organization of the individual is capable through 

 its own laws of growth, under certain conditions, of undergoing great 

 modifications, independently of the gradual accumulation of slight in- 

 herited modifications. 30 



In the last edition of the "Origin of Species, " however, 

 which was published in the year of the author's death, 

 although he introduces this apology: 4 'In the earlier edi- 

 tions of this work I underrated, as it now seems prob- 

 able, the frequency and importance of modifications 

 due to spontaneous variability," 31 he still later inter- 



Specie* and Varieties, their Origin by Mutation," 2d ed., 1906, p. 

 Origin of Species," 5th ed., 1869, p. 151. 



