98 



but originate suddenly without regard to their fitness for the 

 conditions encountered. 



5. As a further development of the last-named idea, the muta- 

 tions by which new species arise are in themselves purposeless, 

 and may differ from the parent in any particular, or, otherwise 

 stated, mutation may take place in any given direction. Conse- 

 quently, the greater number of the newly arisen types perish at 

 once because of their pronounced unfitness for the conditions 

 and competitions which they encounter, and do not reach a 

 second generation. The surviving species must not only show 

 a fitness for meeting the encroachments of existing forms, but 

 must be anatomically and physiologically suitable for the en- 

 vironment. The number of mutants of any plant growing in a 

 state of nature would usually be very much less than that 

 obtained in the cultural operations described, by reason of the 

 customary failure of the greater proportion of the crop of seeds 

 to obtain germination conditions. It is of course possible that 

 the exigencies of sudden erosions, or disturbances of the soil over 

 small areas might occasionally furnish similar conditions to 

 those under which Onagra mutated so abundantly. 



6. The elementary species were found to arise in a number of 

 individuals at the same time. The mutation from a parent type 

 might occur in such manner that the new species would be 

 formed in successive seasons in the same general manner. 



7. Mutability occurs only at certain periods, and a species might 

 continue existence indefinitely without giving rise to new forms. 



In this last-named conclusion de Vries takes a position long 

 held by Darwin that the variability of a species is independent 

 of its environment and that the strengthening effect of use and 

 weakening effect of disuse are in no wise to be considered as 

 direct agents in the development of forms constituting new 

 species. 



The conceptions of de Vries as to the origin of species may 

 be rightly understood only when his analysis of the character or 

 consistency of a species is borne in mind. His interpretations of 

 the facts lead him to the conclusion that the characters of an or- 

 ganism are made up of well-defined and separate units, or ele- 



