300 FILICALES [CH. 



podiaceae), form erect stems several feet in height; but these 

 differ in appearance from the Palm-like type of the Cyatheaceous 

 tree ferns. On the other hand, the thin, almost transparent, 

 leaf of Hymenophyllum tunbridgense and other filmy ferns is 

 a character shared by several species of Todea, Asplenium re- 

 sectum, and Danaea trichomanoides (Marattiaceae) ; the filmy 

 habit is essentially a biological adaptation. 



The form of frond represented by certain species of 

 Gleichenia, characterised by a regular dichotomy of the axis and 

 by the occurrence of arrested buds, is on the whole a trustworthy 

 character, though Davallia aculeata (bearing spines on its rachis) 

 (fig. 232) and Matonid sarmentosa have fronds with a similar 

 mode of branching and also bear arrested radius-buds. A limited 

 acquaintance with ferns as a whole often leads us to regard a 

 certain form of leaf as characteristic of a particular species, but 

 more extended enquiry usually exposes the fallacy of relying 

 upon so capricious a feature. The form of leaf illustrated by 

 Trichomanes reniforme is met with also in Oymnogramme reni- 

 formis and is fairly closely matched by the leaf of Scolopendrium 

 nigripes. The fronds of Matonia pectinata (figs. 227, 228) bear a 

 close resemblance to those of Gleichenia Cunninghami, Adiantum 

 pedatum, and Cheiropteris palmatopedata^. 



The habit, leaf-form, and distribution of Ferns. 



The full accounts of the structure and life-history of the 

 common Male Fern, given by Scott in his Structural Botany and 

 by Bower in the Origin of a Land Flora, render superfluous 

 more than a brief reference to certain general considerations in 

 so far as they may facilitate a study of fossil types. 



In size Ferns have a wide range : at the one extreme we 

 have the filmy fern Trichomanes Goebelianum^, growing on tree 

 stems in Venezuela, with leaves 25 to 3 mm. in diameter, and 

 at the other the tree ferns with tall columnar stems reaching a 

 height of 40 to 50 feet and terminating in a crown of fronds 

 with a spread of several feet. A common form of stem is 

 represented by the subterranean or creeping rhizome covered 



1 Diels (02) fig. 98, p. 188. ^ Giesenhagen (92) p. 179, fig. 3. 



