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 coérdinate. 
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 Eusporangiate, 7.e. the Maratti- 
aceee and Ophioglossacez, 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 
Marattiacez, 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 Lycopodinee and Equi- 
setinezw, the more specialized and modern Leptosporan- 
giate have arisen, and at present they form the prevail- 
