286 MORPHOLOGY OF ANGIOSPERMS 



structures prove to be insufficient; but the problem seems to 

 have reached this contingency now. 



To many, any conclusion as to the origin of the Monocoty- 

 ledons involves that of the Dicotyledons, which they would re- 

 gard as an ancient branch from the Monocotyledon stock. We 

 have already cited reasons why such a view does not commend 

 itself to us, and prefer to regard Dicotyledons as of independent 

 origin. If the two lines have a common origin, it seems to us 

 that the arguments in favor of the derivation of Monocotyle- 

 dons from the more primitive Dicotyledons are the more con- 

 vincing. Both lines to-day include very primitive forms, and 

 the structure of the flower and character of the megasporan- 

 giate archesporium are more primitive among existing Dicot- 

 yledons than among Monocotyledons. Whether Dicotyledons 

 represent an independent angiospermous line, as we prefer to 

 believe, or the primitive Angiosperm stock, it remains to dis- 

 cuss their possible origin. The fact that they emerged from 

 a primitive group called Proangiosperms, which was largely 

 developed in the first period of the Lower Cretaceous, seems 

 to be fairly well established by paleobotany. The question 

 thus concerns the origin of the Proangiosperms. They do 

 not seem to warrant the belief that they represent a common 

 stock from which both Monocotyledons and Dicotyledons have 

 been derived, for the Monocotyledons are believed to have ex- 

 isted in unmistakable forms before the large assemblage of Pro- 

 angiosperms gave rise to unmistakable Dicotyledons. Still 

 less conceivable is it that the Proangiosperms represent the 

 transition forms from Monocotyledons to Dicotyledons, for 

 .nothing in their known structure seems to suggest such a view. 

 That they were derived from Gnetum-\ike forms is discredited 

 by the fact that there is no sure record of the existence of 

 Gnetum at such an early period, and to have given rise to 

 such an assemblage of forms it must have been a conspicuous 

 group. 



If we turn to the earlier groups that were sufficiently prom- 

 inent and at all suggestive of having given rise to the Pro- 

 angiosperms, we encounter the Coniferales, Cycadales, Lycopo- 

 diales, and Filicales. The Gymnosperm-origin of Dicotyledons 

 seems to be most unlikely with the exclusion of Gnetum. At 

 the same time, it might be claimed that Dicotyledons represent 



