﻿Affinities of the Genus Dioncea, Ellis. 113 



very ones where it should receive most attention. From an evolu- 

 tionary standpoint, plants which are near relatives must be consid 

 ered as derived from a common ancestral form. The metropolis of 

 Drosera, the main genus of the family, is in Australia, and probably 

 nine-tenths of all the species of the order are Old World forms. It 

 might be easy to imagine a few of the species of Drosera as reach- 

 ing America from the Old World, but to imagine Dioncea develop- 

 ing from its far-away Asiatic relatives and leaving no intermediate 

 links, or even to imagine a mode by which it could have reached 

 its present habitat, is impossible. Therefore it seems as if its reten- 

 tion in Droseracece was unwise and adverse to principles of classifi- 

 cation and evolutionary ideas. Its transference to another order, 

 Sarraceniacece, is here proposed. 



The chief and essential difference between the genera of Sarra- 

 ceniacece and Dioncea is in the shape of the leaves. The well-known 

 pitcher form is that characteristic of the first, and the blade, with 

 its filaments and contractile power, that of the second. There can 

 hardly be a doubt but that both came from a common ancestral 

 form. If the theory that the leaves of the Sarraceniacece were de- 

 veloped from the hollow petioles of some plant allied to the water- 

 lilies be correct,* then, after the pitcher was partly formed and the 

 hood well developed, the expansion stopped and retrograded, while 

 the blade went on differentiating, the beginning of the Dioncea leaf 

 will be perceived. 



The development of the winged petiole might have been neces- 

 sary for the existence of the plant before it became so exclusively 

 an insect feeder. Darwin considers the cilia and six sensitive fila- 

 ments as having been developed from glandular hairs, like those of 

 Drosera. It seems just as likely that they are modified internal 

 hairs of some water-lily form. While the hairs on the hood and 

 internal surface of Sarracenia were developing in a suitable way, 

 those on the Dioncea branch pursued a different direction. It is 

 probable that at one time hairs covered the whole surface of the 

 Dioncea leaf blade; that in the course of time those near the edges 

 grew into their present ciliate form, while those on the surface de- 



*See article on this subject in Am. Nat., Vol. XIX, p. 567, June, 1885. 



