PHYLOGENY OF ANGIOSPERMS 287 



an independent line from the Gymnosperm-stock, that advanced 

 in the Mime direction and much farther than did the Gnetum- 

 line. At the same time, all the essential morphology of the 

 Gymnosperms is less favorable to such an origin than is that 

 of the heterosporous Pteridophytes. 



The Lvcopodiales certainly deserve serious consideration in 

 this connection. The structures of Selaginella are about as 

 suggestive of Dicotvledons as those of Isoetes are suggestive 



~o *• CO 



of Monocotyledons, the embryo being as distinctly dicotyledo- 

 nous as that of Isoetes is monoeotyledonous, and the seed-like 

 character of the megasporangium supplies a still more striking 

 resemblance. Such a view does not imply that the present com- 

 paratively modern genus Selaginella has given rise to the Pro- 

 angiosperms, but that the latter may have been derived from 

 the same ancient Lycopodium stock. 



The only remaining alternative hypothesis is that mentioned 

 in connection with the origin of the Monocotyledons, namely, the 

 derivation of the Proangiosperms as an independent heteros- 

 porous line from the abundant ancient eusporangiate Filicales, 

 and this view is supported by anatomical testimony. It may 

 be that further knowledge of the Proangiosperms will help to 

 establish such an hypothesis. 



It seems to us that the last two hypotheses deserve the most 

 consideration, as likely to include the future results of investi- 

 gation. 



It should be noted in connection with the origin of Dicoty- 

 ledons that there is much evidence in favor of the view that they 

 include two independent lines. For example, Campbell inclines 

 to the view that one line is derived from the Arales, passing 

 by way of the Piperales and amentaceous groups to the isoear- 

 pous Sympetalae, while the other arises from the apocarpous 

 Helobiales, and by way of the Ranales and later groups cul- 

 minates in the anisocarpic Sympetalae. Although not inclined 

 to accept the origin suggested, the existence of two such inde- 

 pendent lines of Dicotyledons has very much in ks favor, 

 whether derived from the Monocotyledons or not. 



A summary of our present views, as developed in the preced- 

 ing pages, may be stated as follows: The Monocotyledons and 

 Dicotyledons represent two independent lines derived directly 

 from Pteridophyte stock, probably from the Filicales. At the 



