PHILOGENY OF ANGIOSPEKMS 2S1 



pendent lines. Again, the fundamental differences in the de- 

 velopment of the embryos of the two groups are hard to recon- 

 cile upon the theory of monophyletic origin. Add to this the 

 fundamental differences in the structure of the stem and in 

 the character of its vascular bundles, and the derivation of one 

 group from the other seems more inconceivable than the deriva- 

 tion of the Dicotyledons from the Gymnosperms. Still another 

 argument against the monophyletic theory is furnished by the 

 historical testimony. The Proangiosperms of the Lower Cre- 

 taceous, so far as known, appeared associated with undoubted 

 Monocotyledons, and merged gradually into recognizable Di- 

 cotyledons, without indicating any relationship to the Mono- 

 cotyledons. The emerging of Dicotyledons from this vague 

 group either indicates that Monocotyledons and Dicotyledons 

 originated independently, or that the Proangiosperms were 

 transition forms between Monocotyledons and Dicotyledons. 

 This latter alternative is in turn inconceivable, especially since 

 the most primitive Dicotyledons are recognized to be even more 

 primitive than any of the Monocotyledons. 



Recently, however, the morphological arguments in favor 

 of the monophyletic origin of Angiosperms have been reen- 

 forced by anatomical investigations, which point to origin from 

 a common proangiospermous stock, or the derivation of the 

 Monocotyledons from the more primitive Dicotyledons. In the 

 following chapters it will be noted that on anatomical grounds 

 Jeffrey regards the Monocotyledons as strictly monophyletic 

 and modern, derived from the Dicotyledons or their parent 

 stock ; and on the same ground Queva ° thinks that the Mono- 

 cotyledons are derived from the lower Dicotyledons. In her 

 study of the origin of the cotyledon in Monocotyledons, Miss 

 Sargant ls concludes that the Monocotyledons are a specialized 

 branch from the Dicotyledons. In Anemarrhena, one of the 

 Liliaceae, she finds two opposed vascular bundles in the ter- 

 minal cotyledon. These run down into the short hypocotyl, 

 where each divides into two, and the four phloems so formed 

 are continuous with those of the tetrarch primary root. This 

 suggests that two cotyledons are represented, which were sepa- 

 rate in some dicotyledonous ancestor. The same investigator 

 also finds in Erianthis, one of the Ranunculaceae, a possible 

 illustration of this dicotyledonous ancestor ; for the petioles 



