CHAP. VI. REMARKS ON HETEROSTYLED PLANTS. 245 



CHAPTER VI. 

 CONCLUDING EEMAEKS ON HETEROSTYLED PLANTS. 



The essential character of heterostyled plants Summary of the differ- 

 ences in fertility between legitimately and illegitimately fertilised 

 plants Diameter of the pollen-grains, size of anthers and structure 

 of stigma in the different forms Affinities of the genera which in- 

 clude heterostyled species Nature of the advantages derived from 

 heterostylism The means by which plants became heterostyled 

 Transmission of form Equal-styled varieties of heterostyled plants 

 Final remarks. 



IN the foregoing chapters all the heterostyled plants 

 known to me have been more or less fully described. 

 Several other cases have been indicated, especially by 

 Professor Asa Gray and Kuhn,* in which the indi- 

 viduals of the same species differ in the length of 

 their stamens and pistils; but as I have been often de- 

 ceived by this character taken alone, it seems to me 

 the more prudent course not to rank any species as 

 heterostyled, unless we have evidence of more impor- 

 tant differences between the forms, as in the diameter 

 of the pollen-grains, or in the structure of the stigma. 

 The individuals of many ordinary hermaphrodite plants 

 habitually fertilise one another, owing to their male 

 and female organs being mature at different periods, 

 or to the structure of the parts, or to self-sterility, &c. ; 

 and so it is with many hermaphrodite animals, for 

 instance, land-snails or earth-worms; but in all these 

 cases any one individual can fully fertilise or be ferti- 



* Asa Gray, 'American Journ. elsewhere as already referred to. 

 of Science,' 1865, p. 101; and Kuhn, 'Bot. Zeitung,' 1867. p. 67. 



