452 The Ohio Naturalist. [Vol. IX, No. 4, 



pod-like sporangium and with a bulbous foot containing an irre- 

 gular surface with wart-like projections; sporangium with a cen- 

 tral columella, two-valved, with small irregular elaters among the 

 spores ; epidermis with or without stomata ; cells with a single 

 large chloroplast. 



IV. PTERIDOPHYTA HOMOSPORAE. 4,500 species. 



31. Filices. Ferns. 4,000 living species. 



Sporophyte herbaceous or tree-like, usually with a horizontal 

 rhizome, simple or branched ; leaves usually large, alternate and 

 mostlv compound, rarely grass-like; sporangia borne on the 

 under side of the leaves or on simple or branched sporangio- 

 phores ; eusporangiate or leptosporangiate ; sporoph^dls not form- 

 ing "cones. Gametophyte comparatively large, tuber-like with- 

 out chlorophyll and subterranean, or developed as a flat, simple 

 or branched thallus, hermaphrodite or unisexual; spermatozoids 

 multiciliate. 



Subclasses Eusporangiatae 



Lepiosporangiatae . 



32. Equiseteae. Horsetails. 25 species. 



Sporophyte perennial, herbaceous, with a rhizome, and 

 with jointed, mostly hollow, simple or branched, aerial stems 

 which are either annual or perennial ; vascular bundles in a circle ; 

 leaves reduced to sheaths around the joints, the sheaths toothed ; 

 sporangia borne on small peltate sporophylls arranged in whorls 

 on a terminal cone ; eusporangiate ; spores with four narrow, strap- 

 like, hygroscopic appendages. Gametophyte a small green thal- 

 lus, usually unisexual; spermatozoids multiciliate. 



33. Lycopodieae. Lycopods. 155 species. 



Sporophyte perennial, herbaceous, with or without a rhizome, 

 the aerial stems upright or trailing; branching monopodial or 

 dichotomous; leaves small, without a ligule, scattered on the 

 stem, into two to many ranks ; sporangia solitary on the upper sur- 

 face of the leaves or in their axils, eusporangiate; sporophylls 

 in bands alternating with the sterile leaves or arranged in spirals 

 in terminal cones; spores small, not appendaged. Gametoph^•te 

 small, sometimes subterranean, with or without chloroph\-ll, 

 hermaphrodite; spermatozoids biciliate. 



V. PTERIDOPHYTA HETEROSPORAE. 700 species. 



34. Calamarieae. Fossil. 



Paleozoic jjlants, sometimes of tree-like aspect and dimen- 

 sions, with hollow-jointed stems with a circle of collateral vascu- 

 lar bundles; stems increasing in diameter by a cambium zone; 

 heterosporous, the sporophylls in cones. 



