154 EVOLUTION OF PLANTS 



multiciliate spermatozoids of the ferns. There is no 

 very satisfactory evidence of the origin of any of the 

 existing classes from either of the others, although there 

 are certain characters which the lower members of all 

 the series have in common. It is probable that all have 

 originated from either the same or closely related ances- 

 tral forms, but the three classes as they now exist may 

 be considered as coordinate. 



The geological evidence shows conclusively that the 

 club-mosses and horsetails are to be considered as 

 remnants of groups once much more important than at 

 present, which probably reached their maximum devel- 

 opment during the Carboniferous era. 



With the ferns the matter seems different. Of the 

 two main divisions, the Eusporangiatse, i.e. the Maratti- 

 acese and Ophioglossacese, show strong evidence of being 

 primitive forms. This is indicated not only by the 

 large long-lived gametophyte and the form of the re- 

 productive organs, but also by the simplicity of the tis- 

 sues of the sporophyte, especially the undifferentiated 

 sporangia, which show an approach to the condition 

 found in certain liverworts. The evidence of compar- 

 ative anatomy is confirmed by the geological record, 

 which shows conclusively that the oldest fossil ferns 

 were undoubtedly of the eusporangiate type. The 

 Marattiacese, especially, were very much better repre- 

 sented than at present. 



From the primitive eusporangiate stock, which, as 

 might naturally be expected, shows certain affinities 

 with the lower members of the Lycopodinese and Equi- 

 setinese, the more specialized and modern Leptosporan- 

 giatse have arisen, and at present they form the prevail- 



