THE PHYLOGENY OF ANGIOSPERMS 



John M. Coulter 



The views presented in this paper are in the main based upon numerous 

 investigations conducted by members of the botanical stafp and graduate students. 

 The accounts of these investigations, extending through a period of six years, have 

 been published from time to time, chiefly in the Botanical Gazette, but their bearing 

 upon the problem of the phylogeny of Angiosperms has never been presented. It would 

 be confusing to cite the literature involved in this presentation, as it would mean an 

 extensive bibliography and is in the main familiar to students of the Angiosperms. 

 The purpose is to present in as compact form as possible the bearings of our present 

 knowledge upon a problem of great obscurity. The phylogeny of any great group 

 will probably always remain a baffling problem, incapable of actual demonstration, 

 and yet theories of phylogeny serve to co-ordinate knowledge and stimulate investigation. 

 It should be stated that when similarity of structure was taken to be a sure indication 

 of genetic relationships, the problem promised an approximate solution. But since it 

 has been proved that similar structures may develop independently, the difficulty of 

 solution has become apparently insurmountable. 



The first phase of the problem has to do with the common or independent origin of 

 the Monocotyledons and Dicotyledons. The current view assumes their monophyletic 

 origin, a view based largely upon the great uniformity of the peculiar development of 

 the female gametophyte. It is argued that the independent origin of such exact details 

 of development and structures is inconceivable. The peculiar female gametophyte of 

 Angiosperms, however, has been foimd to vary enough to indicate that it is an extreme 

 expression of tendencies evident in the heterosporous Pteridophytes and Gymnosperms ; 

 in other words, an ultimate result of heterospory. Further, nothing is more clear 

 than that heterospory has originated independently in several plant groups; and the 

 assumption that its ultimate expressions, the seed and the angiospermous female 

 gametophyte, have been reached by only one line seems more than improbable. 



This somewhat theoretical objection to the current argument in favor of the 

 monophyletic origin of Angiosperms is strengthened by certain fundamental differences 

 between the Monocotyledons and Dicotyledons. The differences in the development 

 of the embryos of the two groups are hard to reconcile upon the theory of monophyletic 

 origin. Recent investigations of all of those Dicotyledons that have been called 

 "pseudo-monocbtyledonous," on account of their apparently terminal cotyledon and 

 lateral stem-tip, have shown a normal dicotyledonous embryology with more or less 

 complete abortion of one of the cotyledons and displacement of the stem-tip through 

 the development of the functional cotyledon. Again, the differences in the structure 



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