284 FILICALES [CH. 



the sterile, or more or less sharply contrasted, usually bear the 

 sporangia on the under surface of the lamina in definite groups 

 or sori, and not on the upper surface or grouped in strobili as 

 in the Lycopodiales. The stem is dorsiventral or radial in 

 structure, creeping or erect, frequently clothed with chaflfy 

 scales (ramenta) and less often with multicellular hairs. The 

 sexual generation is represented by a small green prothallus 

 which lives for a short period only and dies after nursing the 

 fern-plant through its earliest stages. 



(b) Hydropterideae. Heterosporous water-ferns differing 

 considerably in habit from the true ferns. Each megasporan- 

 gium contains a single megaspore and several microspores are 

 produced in each microsporangium. The gametophyte is repre- 

 sented by tissue more or less enclosed in the spore. [Genera 

 Salvinia, Azolla, Marsilia, Regnellidium, Pilularia. See 

 Chapter xxvi.] 



(tt) Eufilicineae. The classification of the true ferns in 

 common use is based almost exclusively on the structure of the 

 sporangium, the form and position of the sori, and on the 

 presence or absence of an indusium (the tissue which in some 

 ferns partially or completely covers each sorus). In recent 

 years there has been considerable activity in the investigation 

 of fern anatomy with a view to elucidating the natural relation- 

 ship between recent families or genera. The results of these 

 researches are on the whole consistent with the scheme and 

 grouping adopted in the Synopsis Filicum of Hooker and Baker 

 and in general harmony with the main conclusions arrived at 

 by Bower from an intensive study of the development of fern 

 sporangia. The following classification is based on that of 

 Bower who takes as a basis (i) the relative time of appearance 

 of the sporangia in a single sorus, (ii) the structure of the 

 sporangia and their orientation relative to the whole sorus, 

 (iii) the productiveness of sporangia (spore-output). 



Ostnundaceae 

 Sohizaeaceae 

 Gleicheniaceae 

 Matonineae 



Simplices (Bower). The sporangia are relatively 

 large and all the sporangia in a sorus have a 

 simultaneous origin : the annulus is oblique. 



