APPENDIX. 77 



ceeding in the direction of adaptive growth, it is re- 

 markable that the same was not made long ago by 

 some one or other of the many who have thought and 

 written on selection and evolution. 



Allusions to a connexion between the direction 

 of variation and the selective processes are to be found, 

 but they remained unnoticed or undeveloped. I have 

 been able to find at least two such observations, but 

 would not wish to assert that there are not more of 

 them hidden somewhere in the literature of the subject. 

 One of them is old and comes from Fritz Miiller. It 

 was appended by his brother Hermann as a "Supple- 

 mentary Remark" to his book Die Befruchtung der 

 Blunien durch Insecten (1873) and is dated Novem- 

 ber 24, 1872. We read there: "My brother Fritz 

 Muller communicates to me in a letter which reached 

 my hands only after the bulk of the present work had 

 passed through the press, the following law discovered 

 by him, which materially facilitates the explanation by 

 natural selection of the pronounced characters of 

 sharply distinguished species: 'The moment a choice 

 in a definite direction is made in a variable species, 

 progressive modification from generation to genera- 

 tion in the same direction will set in as the result of 

 this choice, wholly apart from the influence of ex- 

 ternal conditions. Transformation into new forms is 

 thus greatly facilitated and accelerated.' 



The facts on which F. Muller based the enunciation 

 of his law, are the results of several experiments with 

 plants, the numbers of whose grains (maize), or styles, 

 or flowering leaves, were, by the exercise of choice in 

 the cultivation, made to change in definite directions. 

 Accurately viewed their significance is the same as 

 that of numerous other cases of artificial selection, for 



