556 Mutations 



thrown away as soon as they showed their dif- 

 ferentiating characters in order to make room 

 for the remaining ones. At last only a few 

 plants were left to blossom in order to perpet- 

 uate the race. I have indicated for each genera- 

 tion the number of mutants of each of the ob- 

 served forms, placing them in vertical columns 

 underneath their respective heads. The three 

 first generations were biennial, but the five last 

 annual. 



PEDIGREE OF A MUTATING FAMILY OF OENOTHERA LAMARCKIANA 

 IN THE EXPERIMENTAL GARDEN AT AMSTERDAM. 



It is most striking that the various mutations 

 of the evening-primrose display a great degree 

 of regularity. There is no chaos of forms, no 

 indefinite varying in all degrees and in all direc- 

 tions. Quite on the contrary, it is at once evi- 

 dent that very simple rules govern the whole 

 phenomenon. 



I shall now attempt to deduce these laws from 



