700 Mutations 



saw it, seventeen years ago. How long had 

 it been so ? Had it commenced to mutate after 

 its introduction into the field where it had 

 run wild, or was it already previously in this 

 state? It is as yet impossible to decide this 

 point. Perhaps the mutable state is much 

 older, and dates from the time of the introduc- 

 tion of the species into Europe, more than a 

 century ago. 



Apart from all such considerations the period 

 of the direct observations, and the possible 

 duration of the mutability through even more 

 than a century, would constitute only a moment, 

 if compared with the w^hole geologic time. Start- 

 ing from this conception the pedigree of our mu- 

 tations must be reduced to a smaller group. 

 Instead of figuring a fan of mutants for each 

 year, we must condense all the succeeding 

 swarms into one single fan, as might be done 

 also for Draba verna and other polymorphous 

 species. In Oenothera the main stem is pro- 

 longed back and beyond the fan ; in the others 

 the main stem is lacking or at least undiscerni- 

 ble, but this feature manifestly is only of sec- 

 ondary importance. "We may prefer the image 

 of a fan, adjusted laterally to a stem, which it- 

 self is not interrupted by this branch. 



On this principle two further considerations 

 are to be discussed. First the structure of the 



