[LIST [Vol. XLIII 



have the appearance, at first, of a move into a region of 

 mystery and uncertainty. The lapse of time and the 

 growth of familiarity with it are necessary to the reclama- 

 tion of a terra incognita. 



Before leaving this branch of my subject, I desire to 

 call your attention to the very interesting fact that Mr. 

 Darwin himself once conducted a long series of experi- 

 ments which, it can hardly be doubted, resulted in the 

 production of mutants and that he just missed the dis- 

 covery of principles which are now the basis of scientific 

 pedigree cultures and are occupying the attention of in- 

 vestigators of the problems of variation and heredity. 

 In a letter to J. H. Gilbert, dated February 16, 1876, Mr. 

 Darwin writes : 



perimenting in crossing and 

 plants: and one indirect result has surprised me much, 

 y taking pains to cultivate plants in pots under glass 

 successive generations, under nearly similar conditions, 

 ilizing them in each generation, the colour of the flowers 

 ami, what is very remarkable, they became in some of the 

 pecies. SU( .h as Mj nm ius. Carnation, &c, quite constant, 

 wild species. This fact and several others have led me 

 to the suspicion that the cause of variation must be in different sub- 

 stances absorbed from the soil by these plants when their powers of ab- 

 sorption are not interfered with by other plants with which they grow 

 mingled in a state of nature. 52 



The point I particularly wish you to notice in this case 

 is that Mr. Darwin was employing practically the 

 methods now used by Professor De Vries, Professor Mac- 

 Dougal and others who are engaged in species testing, 

 by growing naturally variable or mutating plants under 

 conditions of rigid control, so as to exclude crossing or, 

 as De Vries calls it, vicinism. In this view of the matter, 

 it would be interesting to know what percentage of Mr. 

 Darwin's plants exhibited the new and constant char- 

 acters and through how many generations his mutants 

 were found to breed true, for then we could compare his 

 results with those of investigators of our day. But his 

 attention was centered upon the endeavor to find a cause 



""Life and Letters," 1886, Vol. Ill, p. 343. 



Now, for the last ten years I hav 

 Mf-fertilizing plants; and one inc 



