344 GENERAL CONCLUSIONS. Chap. VIIL 



vantageous. It is therefore probable that the two forms 

 in this sub-class have been separated or developed for 

 this special end. 



Various hermaphrodite plants have become hetero- 

 styled, and now exist under two or three forms; and 

 we may confidently believe that this has been efEeeted 

 in order that cross-fertilisation should be assured. For 

 the full and legitimate fertilisabion of these plants pollen 

 from the one form must be applied to the stigma of an- 

 other. If the sexual elements belonging to the same 

 form are united the union is an illegitimate one and 

 more or less sterile. With dimorphic species two ille- 

 gitimate unions, and with trimorphic species twelve 

 are possible. There is reason to believe that the ster- 

 ility of these unions has not been specially acquired, 

 but follows as an incidental result from the sexual ele- 

 ments of the two or three forms having been adapted to 

 act on one another in a particular manner, so that any 

 other kind of union is inefficient, like that between dis- 

 tinct species. Another and still more remarkable inci- 

 dental result is that the seedlings from an illegitimate 

 union are often dwarfed and more or less or completely 

 barren, like hybrids from the union of two widely dis- 

 tinct species. 



