338 Origin of Each Species Considered Separately. 



fact cannot explain the difference in the mutation-co- 

 efficients. 



Fig. 71. Oenothera oblonga. Upper and middle section 

 of a plant in September to show the peculiar type of 

 branching with rosette-like lateral branches, (Compare 

 Fig. 67 on page 329.) Reduced to Vs natural size. The 

 smaller figures similarly reduced, a, a flower ; a petal is 

 removed and shown separately at b; c, a flower without 

 the corolla, showing the stamens which are bent down- 

 wards at the base but upwards again towards their tips, 

 and the style with the four stigmata; d, ripe fruits; e, 

 one of their bracts. 



These differences in the "mutation coefficients" hold 

 good, too, of the individual families. Not exactly of 

 course, but to such an extent that in large sowings the 



