Periodic Mutations 703 



fittest, the law of the selection of species, which 

 we have already laid stress upon more than 

 once. 



Our second consideration is also based upon 

 the frequent repetition of the several mutations. 

 Obviously a common cause must prevail. The 

 faculty of producing nanella or lata remains the 

 same through all the years. This faculty must 

 be one and the same for all the hundreds of mu- 

 tative productions of the same form. When 

 and how did it originate ? At the outset it must 

 have been produced in a latent condition, and 

 even yet it must be assumed to be continuously 

 present in this state, and only to become active 

 at distant intervals. But it is manifest that 

 the origiual production of the characters of 

 Oenothera gigas was a phenomenon of far great- 

 er importance than the subsequent accidental 

 transition of this quality into the active state. 

 Hence the conclusion that at the beginning of 

 each series of analogous mutations there must 

 have been one greater and more intrinsic mu- 

 tation, which opened the possibility to all its 

 successors. This was the origination of the 

 new character itself, and it is easily seen that 

 this incipient change is to be considered as the 

 real one. All others are only its visible ex- 

 pressions. 



Considering the mutative period of our even- 



