Experimental Pedigree-Cultures 557 



my experiment. Obviously they apply only to 

 our evening-primroses, but may be expected to 

 be of more general validity. This is at once 

 manifest, if we compare the group of new mu- 

 tants with the swarms of elementary forms 

 which compose some of the youngest systematic 

 species, and which, as we have seen before, are 

 to be considered as the remains of previous mu- 

 tations. The difference lies in the fact that the 

 evening-primroses have been seen to spring 

 from their ancestors and that the drabas 

 have not. Hence the conclusion that in com- 

 paring the two we must leave out the pedigree of 

 the evening-primroses and consider only the 

 group of forms as they finally show themselves. 

 If in doing so we find sufficient similarity, we are 

 justified in the conclusion that the drabas and 

 others have probably originated in the same way 

 as the evening-primroses. Minor points of 

 course will differ, but the main lines cannot have 

 complied with wholly different laws. All so- 

 called swarms of elementary species obviously 

 pertain to a single type, and this type includes 

 our evening-primroses as the only controlled 

 case. 



Formulating the laws of mutability for the 

 evening-primroses we therefore assume that 

 they hold good for numerous other correspond- 

 ing cases. 



