CHAPTER XX. 



FILICALES. 



This division of the Pteridophyta includes both the true 

 ferns (Filicineae) and the less familiar water-ferns or Hydro- 

 pterideae. The almost complete absence of satisfactory evidence 

 in regard to the geological history of the latter renders this 

 group of secondary importance from a palaeobotanical stand- 

 point, but, on the other hand, we possess a wealth of material 

 bearing on the past history and relative antiquity of the true 

 ferns. 



The study of extinct types has so far rendered no sub- 

 stantial help towards bridging the wide gap between the 

 Filicales and the lower plants. As Mr Tansley^ says in his 

 admirable lectures on The Evolution of the Filicinean Vascular 

 System, " The biggest gap in the plant kingdom at the present 

 time is undoubtedly that which separates the Pteridophytes 

 from the plants definitely below them in organisation, and 

 directly we try to step behind the ferns we tumble into this 

 abyss." Resemblances long ago recognised between certain 

 ferns and the cycads, a section of the Gymnosperms, were 

 regarded by a few botanists as indications of blood-relation- 

 ship, and the results of recent researches into the morphological 

 characters of extinct Palaeozoic types are generally held to 

 confirm these surmises. Prof. Chodat^ of Geneva has recently 

 challenged the validity of the arguments on which the 

 affinity of cycads and ferns has been accepted by the great 

 majority of botanists. Whether or not his criticisms stand the 



1 Tansley (08) p. 3. Cf. Braun (75) p. 267. = Chodat (08). 



