X FILICINE^ LEPTOSPORANGIAT^E 307 



modified sporophylls. Usually, but not always, each group of 

 sporangia (sorus) covered by a special covering, the indusium. 

 Order I. Filices. 



Family i. Osmundaceae. 

 Family 2. Gleicheniaceae. 

 Family 3. Hymenophyllacea^. 

 Family 4. Schizgeacese. 

 Family 5. Cyatheaceae. 

 Family 6. Polypodiaceae. 



II. Heterosporous forms, cither aquatic or amphibious ; the 

 prothallia are always dioecious, the female prothallium with 

 chlorophyll and capable of more or less independent growth 

 when not fertilised ; male prothallium always without chloro- 

 phyll, the vegetative part reduced to one or two cells, besides 

 the antheridium. Leaves either circinate (Marsiliaceae) or 

 folded (Salviniaceae) ; sporangia without an annulus and borne 

 in special " sporocarps," which are either modified branches of 

 ordinary leaves (Marsiliaceae) or a very highly developed 

 indusium. 



Order II. Hydropterides. 



Family i. Marsiliaceae. 

 Family 2. Salviniaceae. 



Order I. Filices 



The six families of the Filices form an evidently very 

 natural group, but there has been a good deal of disagreement 

 as to their relative positions. The Osmundaceae are generally 

 recognised as approaching most nearly the eusporangiate Ferns, 

 and the Gleicheniaceae come next to these. The Hymeno- 

 phyllaceae are usually considered at the other extreme of the 

 series, but there are a number of reasons why this seems doubtful, 

 and I am inclined to assign them an intermediate position. 

 Their structure and development give evidences of their being 

 a specially modified group adapted to living in very damp 

 situations, and they probably cannot be regarded as connecting 

 any of the other families, but rather as a side branch which has 

 developed in a direction away from the type. They come 

 nearest the Gleicheniaceae and Osmundaceae in the structure of 

 the sexual organs, and the sporangium shows points in common 



