150 Plant Life and Evolution 



they rapidly increase in number and variety, 

 and many existing genera can be plainly recognized 

 among these Cretaceous fossils. So far as the evi- 

 dences of geology go, the two great divisions of 

 angiosperms Monocotyledons and Dicotyledons 

 seem to be of about equal antiquity, and practically 

 no light is shed on the relationships of these two 

 groups to each other from a study of their fossil 

 remains. Nor are there any evidences of fossil 

 remains intermediate between angiosperms and 

 gymnosperms, unless some of the cycad-like forms 

 of the Mesozoic are to be so regarded, and this at 

 present is at least doubtful. Equally unsatisfactory 

 are the attempts to derive the angiosperms from 

 any of the existing gymnosperm types. 



The Earlier Fossil Angiosperms. The sudden 

 appearance of the angiosperms in the Sub-Cre- 

 taceous formations, and the close resemblance of 

 these earliest fossils to living forms, makes it quite 

 likely that the earliest angiosperms have left no 

 visible traces in the rocks. This may be due either 

 to the perishable nature of these primitive forms, 

 which were, perhaps, delicate herbaceous plants, like 

 many of the existing monocotyledons, or such low 

 dicotyledons as the buttercups and some of the pep- 

 pers; or it may be that the primitive forms lived 

 in relatively dry localities where the conditions for 

 fossilization were not favorable. 



The Flower. The flower of the angiosperms is 

 a much more highly developed structure than that 



