CHAP. IV. LYTHRUM SALICAKIA. 149 



longer papillae or is rougher than that of the mid- 

 styled, and the latter than that of the short-styled ; 

 but this character, though fixed and uniform in the 

 two forms of Primula veris, &c., is here variable, for 

 I have seen mi4-styled stigmas rougher than those 

 of the long-styled.* The degree to which the longest 

 and mid-length stamens are graduated in length and 

 have their ends upturned is variable ; sometimes all 

 are equally long. The colour of the green pollen in 

 the longest stamens is variable, being sometimes pale 

 greenish-yellow ; in one short-styled plant it was almost 

 white. The grains vary a little in size : I examined 

 one short-styled plant with the grains above the 

 average size ; and I have seen a long-styled plant with 

 the grains from the mid-length and shortest anthers of 

 the same size. We here see great variability in many 

 important characters; and if any of these variations 

 were of service to the plant, or were correlated with 

 useful functional differences, the species is in that 

 state in which natural selection might readily do much 

 for its modification. 



On the Power of Mutual Fertilisation lehceen the three 

 Forms. 



Nothing shows more clearly the extraordinary com- 

 plexity of the reproductive system of this plant, than 

 the necessity of making eighteen distinct unions in 

 order to ascertain the relative fertilising power of the 



* The plants which I observed and he appears to have found the 

 grew in my garden, and probably stigmatic papillae differing con- 

 varied rather more than those stantly in length and structure in 

 growing in a state of nature. H. the three forms, being longest in 

 Miiller has described the stigmas the long-styled form, 

 of all three forms with great care, 



