XVII SUMMARY AND CONCLUSIONS 6or 



plex, shows that in the former also it is not improbable that the 

 spike is really terminal, and the lamina of the leaf a lateral 

 appendage of it as it is assumed it must have been in the ances- 

 tral form. 



While the Lycopodineae correspond closely to the Bryo- 

 phytes in the form of the spermatozoids, these in the other 

 Pteridophytes are large and multiciliate. Whether these pecul- 

 iarities have arisen independently in the Filicinese and Ecjuise- 

 tinese, or whether thev are inherited from some common ances- 

 tor, there is no means of deciding, but the latter view is prob- 

 ably the correct one, and it is likely that the two classes have 

 a common, but extremely remote origin. None of the 

 Muscinese, so far as is known, depart from the biciliate type, but 

 among Algae CEdogonhim offers a similar exception to the 

 usual biciliate form. 



The Lycopodiacese and Selaginelleae constitute a sufficiently 

 direct series, but the exact affinity of the Psilotaceae to these is 

 by no means clear. Our complete ignorance of the sexual stage 

 of the latter, as well as their parasitic habit, makes it impossible 

 to judge just how far their simple structure is primary and how 

 much is due to reduction. More evidence also is required in 

 regard to their assumed affinity with the Sphenophyllaceae. 



The reasons for regarding the eusporangiate Ferns as the 

 lowest of the Filicineae have already been given at length, but 

 may be summarised as follows: (i) The structure of the 

 gametophyte and sexual organs corresponds more nearly to that 

 of the Liverworts than do those of the Leptosporangiatae, and 

 the prothallium is larger and longer lived than in the latter; (2) 

 the embryo remains much longer dependent upon the gameto- 

 phyte, and the latter may live for a long time after the sporo- 

 phyte becomes independent; (3) the differentiation of the 

 organs and tissues of the embryo takes place later than in the 

 Leptosporangiates, and the tisslies of the mature sporophyte are 

 also simpler than in most of the latter ; (4) the sporangia of the 

 Eusporangiatae, especially Ophioglossum, are of a much less 

 specialised type than in the typical leptosporangiate Ferns, and 

 approximate more nearly the condition found in Anthoceros; 

 (5) the small number of species of the Eusporangiatae, but the 

 wide divergence of type shown, especially by the two groups of 

 the Ophioglossaceae and Marattiaceae, indicate that these are 

 remnants: of formerly more predominant forms. Finally, the 



