Origin of Different Kinds of Adaptations 365 



Illegitimate plants from short-styled parents were dwarfed 

 in stature, and often had a weakly constitution. They were 

 not very fertile inter se, and remarkably infertile when legiti- 

 mately fertilized. This kind of result, where a difference in 

 the power of mutual intercrossing exists between two forms, 

 recalls in many ways the difference in the results of cross- 

 ing of different species of animals and plants, especially those 

 cases in which a cross can be made in one way more success- 

 fully than in the other. 



The heterostyled trimorphic plants, of which Lythrum 

 salicaria, Figure 5 C, D, E, may be taken as an example, are 

 even more remarkable. There are three different kinds of 

 flowers : in one the pistil is long and there is a medium and 

 a short set of stamens ; in another the pistil is of intermedi- 

 ate length and there is a long set and a short set of sta- 

 mens ; in the third kind the pistil is short, and there is a 

 medium and a long set of stamens. There are possible only 

 six sorts of legitimate unions between these three sets of 

 flowers. No less than twelve kinds of illegitimate unions 

 may occur. In regard to the difference in the sizes of the 

 pollen grains, those from the long-styled form are the largest, 

 from the mid-styled form next, and from the short-styled 

 form the smallest. The extreme difference is as 100 to 60. 

 " Nothing shows more clearly the extraordinary complexity 

 of the reproductive system of this plant than the necessity of 

 making eighteen distinct unions in order to ascertain the rela- 

 tive fertilizing power of the three forms." Darwin tried the 

 effect of each of these combinations, making 223 unions in 

 all. The results are surprising. Comparing the outcome 

 of the six legitimate unions with the twelve illegitimate ones, 

 the following results were obtained : — 



