89 



for the abrupt variations and not on the formulation of 

 laws of their action. Apparently he considered isolation 

 to be the principal secondary cause or favoring condition, 

 upon which view the obvious comment is that it requires 

 no great stretch of imagination to conceive of similar 

 isolation as occurring in nature and thus favoring muta- 

 tion among uncultivated forms. 



Having now hastily reviewed the oscillations in Dar- 

 win's opinions concerning the kinds, the causes and the 

 laws of variation with relation to the origin of species, it is 

 not my purpose to enter upon a discussion of the present- 

 day mutation theory, which has grown out of a closer 

 study, and a more scientific treatment, of the problems of 

 variation and heredity than were attempted, or were 

 perhaps possible in Darwin's time. It is desirable, how- 

 ever, to compare Darwin's views with generalizations 

 from the mutation theory, which we can do, well enough 

 for our present purpose, by merely recalling the seven 

 laws which De Vries claims to be the logical outcome of 

 his twenty years of cultural experiments upon plants. 

 They are, with slight modifications as to wording and 

 order, as follows : 



1. New elementary species appear suddenly without 

 intermediate steps. 



2. New forms spring laterally from the main stem. 



3. New elementary species attain their full constancy 

 at once. 



4. Some of the new strains are elementary species, 

 while others are to be considered as retrograde varieties. 



5. The same new species are produced in a large num- 

 ber of individuals. 



6. Mutations take place in nearly all directions and are 

 due to unknown causes. 



7. Species and varieties have originated by mutation, 

 but are, at present, not known to have originated m any 

 other way. 



Now, looking back over what Darwin wrote concerning 

 variation, I can not believe that he would seriously have 



