6 14 STRUCTURE AND LIFE HISTORIES^ 



A consideration of the fossil record, however, makes it 

 difficult to accept this hypothesis. Not only do we find, 

 in the fossil forms described above, sporophytes that do 

 not bear the remotest resemblance to the moss-sporo- 

 gonium, but fossil mosses and liverworts have never been 

 positively identified in either the Palaeozoic or the Meso- 

 zoic rocks, while the same rocks are rich in fossils of such 

 advanced forms as the broad-leaved sporophytes of the 

 Cycadofilicales and Cycadophytes. We must not, how- 

 ever, hastily conclude, from this lack of evidence, that 

 mosses and liverworts did not exist in those early ages. 

 Quite likely they were present when the Paleozoic rocks 

 were being deposited, though doubtless not represented by 

 the same genera, or at least not by the same species, as 

 are now living. 



527. Summary of Results. — From what has been said, 

 in this and in Chapter XXXVI, we recognize that the 

 method of evolution is to be ascertained chiefly by experi- 

 ment — by studying living plants in action; but the 

 course of evolution chiefly by the study of comparative 

 morphology, with special attention to fossil forms. Other 

 points are necessary to complete the history of the 

 evolution of plants; the above paragraphs give only the 

 barest outline of the problem, for the entire history is 

 much too long and much too difficult to be treated here. 

 To summarize; the facts now known have led some 

 investigators to infer: 



1. The origin of Angiosperms from Cycadophyta (pro- 

 angiosperms) . 



2. The origin of Cycadophyta from CycadofiHcales. 



3. The origin of Cycadofilicales from Primofilices. 



4. The origin of Filicales from Primofilices. 



