PHYLOGENY OF AXGIOSPERMS 



9.R3 



the cotyledon maintained by Lyon 17 be true (see Chapter IX), 

 the Monocotyledons are more primitive than the Dicotyledons 

 and have given rise to them. 



It is an old view, however, that the Dicotyledons are the 

 more primitive, and that the Monocotyledons have been derived 

 from them as a reduction series. Later the relatively primi- 

 tive character of the Monocotyledons was maintained without 

 serions opposition. A detailed presentation of the phylogeny 

 of Angiosperms from this point of view may be found in 

 Bessey's :j " Phylogeny ami Taxonomy of the Angiosperms." 



In our judgment the evidence is strongly in favor of the 

 independent origin of the two groups, which have attained prac- 

 tically the same advancement in the essential morphological 

 structures, but are very diverse in their more superficial 

 features. Their great distinctness now indicates either that 

 they were always distinct or that they originated from forms 

 that were really Proangiosperms and neither Monocotyledons 

 nor Dicotyledons. It may be well to state in this connection 

 that in speaking of the origin of one great group from another, 

 the former is not supposed to have arisen as a single branch. 

 For example, to say that Monocotyledons have been derived 

 from Dicotyledons does not imply that a single monocotyled- 

 onous branch arose from some definite group of the Dicotyle- 

 dons, hut that probably several monocotyledonous lines arose 

 from one or more regions of the Dicotyledons, regions that 

 may or may not be illustrated by living groups. 



The next phase of the problem raises the question whether 

 the Angiosperms have been derived from the Gymnosperms or 

 directly from the Pteridophytes. The general question is the 

 same whether one believes in their monophyletic character or 

 not. The older view is that the Angiosperms have been derived 

 from the Gymnosperms, and Gnetum has been regarded as the 

 nearest living representative of a transition condition between 

 Gymnosperms and Angiosperms. The argument is based upon 

 certain resemblances of Gnetum to the Angiosperms, chief 

 among them being the absence of archegonia, the organization 

 of eggs while the gametophyte consists of free cells, the presence 

 of a perianth and true vessels, and the Dicotyledon-like leaves. 

 This showing is strong but perhaps not conclusive. If this 

 origin be maintained, it is evident not only from the leaf char- 



