CHAP. IV. LYTHRUM SALICARIA. 149 



I have seen mid-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 between 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 

 three forms. Thus the long-styled form has to be fer- 

 tilised with pollen from its own two kinds of anthers, 

 from the two in the mid-styled, and from the two in 

 the short-styled form. The same process has to be 

 repeated with the mid-styled and short-styled forms. 

 It might have been thought sufficient to have tried on 

 each stigma the green pollen, for instance, from either 



* 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, 



