No. 495] CONSTANCY OF MUTANTS 



177 



experiments of American agriculture show that pure 

 strains or varieties of close-bred stocks, especially those 

 of cereals, are sufficiently stable to he held to form under 

 intelligent culture, but none of us, as yet, can say further 

 than this. If we maintain and can agree that a mutation 

 or change has a natural cause and that no plants are 

 stable, constant in character, it is nevertheless not neces- 

 sary to be assumed that the burden of proof rests en- 

 tirely upon Darwinians. 



What evidence may be placed over against the theory 

 of constant elementary species.' Well, as an hypothesis, 

 when carried to the limit, an elementary species becomes 

 a unit character and when unit characters are well known 

 they will as in the case of the units of matter, perhaps 

 become so intelligible as to be recognized as the least 

 conceivable element of natural force which makes for 

 union and which in case of the organic units may make 

 for a heritable change. This, the writer believes, is the 

 ultimate result to which most of DeVries' facts and ob- 

 servations point, and my own observations, together with 

 those of others, as I undestand them, teach that when- 

 ever physical and chemical conditions are changed in 

 the least, within or without the plant, some variation 

 will occur in plant substance, and that this may result 

 in a change in the progeny which may be fixed or modi- 

 fied sufficiently to serve agricultural purposes, if the con- 

 ditions which originate it may be ascertained and reason- 

 ably maintained. It is but reasonable that some changes 

 should approach greater stability than others. 



The practical breeders of America, years before the 

 work at Amsterdam and Svalof commenced, developed 

 hundreds of varieties; and though I have worked with 

 many varieties and strains of wheat, flax and potatoes 

 and have found them all reasonably stable if given gen- 

 erally stable environment, I have never yet been sure 

 that I have seen a stable plant or stable strain or variety. 

 Some change is continually taking place and any change, 

 I think, may be fixed just in proportion as we know the 

 conditions which originate it. 



