368 Causes and Course of Organic Evolution 



but which later separated into two distinct and diverging 

 series. In later Jurassic times then, the forerunners of some 

 of the dicotyledonous and monocotyledonous families must 

 have become fairly abundant, and by combined structural 

 adaptations to environal conditions must have begun to press 

 on and excel the preexisting filicineous and gymnospermic 

 floras. 



The occurrence of an evident and fairly rich angiospermic 

 flora in the Potomac beds of x\merica, and in the Aptian beds 

 of Europe, brings up the necessary corollary that their pro- 

 genitors must have been evolving into dicotyledons and mono- 

 cotyledons during Jurassic times. As yet however no remains 

 from these rocks have been obtained, so that we must rely 

 on morphologic and taxonomic details presented by recent 

 plants, as well as determinations of scant fossils from more 

 recent strata. 



But, as regards the identifications of many fossils from 

 cretaceous and tertiary strata, the writer is compelled to claim 

 a very conservative attitude. Many of these identifications 

 have been made from leaves alone; in a few cases only have 

 flowers or fruits been secured. But the state of preservation 

 of the last is often very imperfect. Where specimens are 

 found that evidently and frequently show a typical parallel 

 or reticulate venation, there seems a fair likelihood that these 

 are monocotyledons or dicotyledons respectively. But the 

 attempt, from study of the leaves alone, to refer many remains, 

 even from the cretaceous rocks, to such genera as the oleander, 

 holly, and guelder-rose, can only give rise to false hopes and 

 mistaken conclusions. 



The arguments for and against a more primitive origin of 

 angiosperms from plants with preponderatingly dicotyledonous 

 details have been ably presented by Henslow and Sargent. 

 We can only attempt now to add suggestions that may fortify 

 that position. And such largely center round three questions. 



First: If the cordaital and protoangiospermic stocks pos- 

 sessed embryos with two cotyledons — as we know the former 

 at least to have had — what causes operated to effect absorption 

 of one cotyledon, and bring the other into a terminal axial 

 position.^ Second: How was the vascular bundle-ring of cor- 

 daital and protoangiospermic ancestors redistributed and 



