FILICALES. 71 



one of the branches there appear to be slight indications of the 

 presence of smaller leaves in addition to the larger ones, suggesting 

 a comparison with Selaginella. 



Cloughton. ean Coll. 



V. 3675. A good specimen, showing the manner of branching 

 and spreading habit of growth. Lower Sandstone, Cloughton. 



Class FILICALES. 



Stem comparatively small in proportion to the size of the leaves. 

 The members of this class are usually isosporous, but in a few 

 forms heterosporous ; sporangia borne on leaves which are either 

 identical with the foliage leaves or more or less modified. Hoots 

 developed from the stem in acropetal succession, or borne on the 

 leaf-stalks. The stem may be either polystelic or monostelic. 



Sub-Class FILICES. 



Order LEPTOSPORANGIAT^. 



The Filices or true Ferns are isosporous. The spores on 

 germination produce a green independently growing prothallus, 

 bearing the sexual organs. Leaves relatively large, in nearly all 

 cases with circinate vernation, bearing scaly ramenta or filamentous 

 hairs ; the sporangia are usually in groups or sori, either naked or 

 enclosed by an indusium, borne on leaves which may be identical 

 with, or more or less distinct from, the vegetative leaves. With 

 a few exceptions the sporangia possess a well-marked annulus ; 

 each sporangium is formed from a single epidermal cell. Stem 

 horizontal and creeping, oblique or vertical, bearing scattered 

 fronds or terminating in a crown of leaves. 1 



1 Vide Seward (94), p. 35, for a general "Introduction to the Filices." 



