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 
mostly compound, rarely grass-like; sporangia borne on the 
under side of the leaves or on simple or branched sporangio- 
phores; eusporangiate or leptosporangiate; sporophylls 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 
multieiliate. 
Subclasses Eusporangiatae 
Leptospo ra ngiatae. 
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 multieiliate. 
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; sporophvlls 
in bands alternating with the sterile leaves or arranged in spirals 
in terminal cones; spores small, not appendaged. Gametophyte 
small, sometimes subterranean, with or without chlorophyll, 
hermaphrodite; spermatozoids biciliate. 
V. PTERIDOPHYTA HETEROSPORAE. 700 species. 
34. Calamarieae. Fossil. 
Paleozoic plants, 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. 
