ORIGIN OF SPECIES 615 
been believed by many persons to be always due to hybridization, 
I refer to the following facts as proof that there was no cross-fer- 
tilization in either of the two cases mentioned, and that the new 
form is therefore not a hybrid. In neither of the two cases men- 
tioned was any other variety of tomatoes grown with those which 
I planted, and no other grew in my neighborhood. Wind, or in- 
sect cross-fertilization was therefore quite improbable. Because I 
personally gathered, preserved and planted all my seed and culti- 
vated all my plants, I am sure no substitution of either seed or 
plants occurred. The fact that in both those cases of mutation 
every plant of the whole crop partook equally of that act is itself 
proof that cross-fertilization did not occur. If my Acme plants 
had received adventitious pollination, or if pollen had reached 
them from any other flowers than those of their connate crop as- 
Sociates, the results of that cross-fertilization would necessarily 
have been incomplete as to the whole crop. It would also have 
been various as to the kinds of hybrids produced had the pollen 
come from more than one variety. Even if it were credible that 
the first case of complete mutation of the whole crop might have 
been the result of cross-fertilization from some unknown source, 
it would still be too much to believe that exactly the same result 
could have been produced a second time in successive years by 
Such adventitious means. Therefore the question of hybridity is 
eliminated. 
The origination of this new form was, in both instances, salta- 
tory. It occurred in correlation with the ordinary function of in- 
traspecific reproduction and was therefore accordant with both 
physiological and phylogenetic law. It did not result from cross- 
fertilization, and it is therefore assumed to have been a spontaneous 
Tesult of some not yet ascertained exciting cause, and primarily 
due to some unknown determinate or predisposing cause. 
After I had reached the foregoing conclusion as to the nature 
of the mutations which I had witnessed, public announcement 
was made of the publication of Professor de Vries’ theory of 
mutation already referred to, and I at once began a comparison 
of his theory and observations with my observations which are 
described in the foregoing paragraphs. This comparison con- 
vinced me that my cases of mutation are similar in fundamental 
