XX ] OSMUNDACEAE 285 



(Gradatae (Bower). Sporangia arise in basipetal 

 succession on a more or less elongated receptacle 

 (portion of the leaf lamina which projects as a 

 cushion or column on which the sporangia are 

 borne) ; annulus oblique ; indusium, if present, 

 in the form of a cup or flap of tissue arising from 

 the base of the sorus. 



Cyatheaceae 

 Denustaedtiinae 



(Mixtae (Bower). This division includes the Poly- 

 podiaceae, by far the largest family of ferns. 

 Polypodiaceae ) '^^^ sporangia are characterised by their rela- 



Parkeriaceae \ ^^'^^^y small size, the presence of a slender stalk, 



the absence of regular orientation or sequence 

 in development, and by the presence of a vertical 

 annulus. 



/The Dipteridinae include species with the characters 

 Dipteridinae \ of the Mixtae, and one species in which the 



( sporangia develope simultaneously {Simplices). 



Osmundaceae^ (Osmunda, Todea.) 



Sporangia large and rather stouter than those of other 

 Leptosporangiate ferns, borne in small groups (filmy species of 

 Todea) in linear and frequently confluent sori {Todea harhara ; 

 fig. 221, D) or clustered round the axis of modified fertile 

 pinnae with much reduced lamina (Osmunda). The annulus is 

 represented by a group of thicker-walled cells a short distance 

 below the apex (fig. 221, C). This family stands apart among 

 the ferns ; in some respects, e.g. in the more robust sporangia 

 occasionally forming synangia, and in the presence of stipular 

 wings, it forms a transitional series bet^reen the Leptosporangiate 

 and Eusporangiate ferns. The only European species of Osmunda, 

 0. regalis, is almost cosmopolitan in range ; other species occur 

 in North and South America, in the Far East, the Malay 

 Peninsula, and in other regions, more especially in the 

 temperate zones. Todea is represented by (i) the South 

 African and Australian species, T. harhara, a fern with a stem, 

 which may reach a height of several feet, thickly covered with 

 adventitious roots and bearing large and somewhat leathery 



^ For a fuller account of recent ferns, see Engler and Prantl (02), Christ (97), 

 Hooker and Baker (68), and Bower (00) (08). 



