CHAPTER XXXIV. 



OSMUNDACEAE. 



THE Osmundaceae are represented by the living genera Osmnnda and 

 Todea, while certain species of the latter are sometimes separated under 

 the generic name of Leptopteris. The number of species is ten. The order 

 is of wide geographical distribution, but outside the limits of the ice-cap 

 of the glacial period. The plants are all perennial, with an upright, but 

 usually short stock, which bifurcates occasionally. The axis is covered by 

 the persistent and winged bases of the leaves, which are disposed upon 

 it in a dense spiral. The attachment to the soil is maintained by numerous 

 stout and darkly-coloured roots, which originate in close relation to the 

 leaf-bases. The leaves expanded in the current year form together a shuttle- 

 cock-shaped group, the outermost of which are often sterile, and the inner 

 fertile ; but some of the leaves never attain full development, their lamina 

 being abortive : these lie at the outside of the winter bud, and their basal 

 region, which remains persistent, acts as a scale-like protection to those 

 within. The leaves show the usual circinate vernation, and are covered 

 while young by mucilage-secreting hairs, which take the place of ramenta. 

 These hairs fall off as the leaf expands, leaving a smooth surface. The 

 leaves themselves are singly or doubly pinnate. In Todea there is no 

 marked difference between the fertile and the sterile regions, but in 

 Osmunda the sporangia are localised on various parts of the leaf, which 

 then show a considerably smaller expansion of surface (Fig. 293). There 

 is a difference of texture of the leaves which has given the basis for the 

 recognition of the third genus, Leptopteris : while Osmunda and Todca 

 barbara have leaves of a leathery character, those species from Australasia 

 and the South Sea Islands which are grouped under Leptopteris show a more 

 or less thin and pellucid structure of the pinnules, an approach to the 

 " filmy" character seen in the Hymenophyllaceae. It is, however, a question 

 whether this difference deserves generic recognition. It is probably a 

 relatively direct and recent adaptation to life under conditions of excessive 

 moisture. The leaves of b'erns are typically winged structures throughout 



