CHAPTER XXIII. 



HETEROSTYLISM.* 



Dimorphic Flowers. — A large portion of Mr. Darwin's work 

 on the " Forms of Flowers " deals with the varieties and phe- 

 nomena of heterostylism, which is specially characteristic of 

 the Primulacem, and Rubiacece, though several instances exist 

 in other orders as well. He and Mr. J. Scott were mainly 

 interested in showing that " illegitimate " or homomorphic 

 unions were less prolific than " legitimate " or heteromorphic ; 

 and inferentially took occasion to describe the differential 

 sexual characters of the forms of the same species. With 

 regard to this latter fact, when Mr. Darwin experimented 

 with wild Cowslips, he first thought that they were tending 

 towards a dioecious condition, and that the long-styled plants 

 were more feminine in nature, and would produce more seed : 

 conversely, that the short-styled plants were more masculine. 

 Contrary to his anticipation, of plants marked growing 

 in his garden, in an open field, and in a shady wood, the 

 short-styled forms gave most seed, the weight of seed being 

 in the proportion of 41 to 34 ; that is, the short-styled pro- 

 duced more seed than the long-styled in the proportion of 

 nearly 4 to 3. Similarly when a number of wild plants w^ere 



* Heterostyled, i.e. plants with stamens and styles of different but 

 corresponding lengths on separate plants. 



Homostyled, i.e. when stamens and styles are of the same length. 



Homo-, di., tri; poly., and hetero-morphic, i.e. flowers of the same, 

 two, three, many, and different forms, respectively. 



