Feb., 1909.] 
The Classification of Plants, IV. 
453 
35. Sphenophylleae. Fossil. 
Paleozoic plants of tree-like aspect and dimensions, with solid 
jointed stems with a central triarch vascular bundle; leaves wedge 
shaped, comparatively small; probably heterosporous, the 
sporophvlls in cones. 
36. Hydropterides. Water-ferns. 75 species. 
Sporophyte with a horizontal rhizome or floating on the sur¬ 
face of the water; leaves alternate or whorled; microsporangia 
and megasporangia borne together enclosed in sporocarps, lep- 
tosporangiate. Gametophytes developing entirely within the 
spore walls or protruding only slightly, very short lived; sperma- 
tozoids large, spirally coiled, multiciliate. 
37. Isoeteae. Quillworts. 60 species. 
Sporophyte with a short tuberous stem with a peculiar type 
of secondary thickening and with long, erect, grass-like leaves 
which have a ligule; roots dichotomous; microsporangia and 
megasporangia large, borne singly, sunken in the expanded bases 
of the leaves, eusporangiate. Gametophytes very much reduced; 
spermatozoids spirally coiled, multiciliate. 
38. Selaginelleae. Selaginellas. 500 species. 
Sporophyte dorsiventral or erect, with monopodial or dicho¬ 
tomous branching and dichotomous roots; leaves small, opposite 
or spirally arranged, ligulate; cells often with a single ehloro- 
plast; sporophvlls in bisporangiate cones, the eusporangiate 
microsporangia and megasporangia single in the axils of the 
sporophvlls. Gametophytes small and short-lived; sperma¬ 
tozoids very minute, biciliate. Some fossil species developed as 
large trees with secondary thickening by a cortical meristem. 
VI. GYMNOSPERMAE. 500 living species. 
39. Pteridospermae. Fossil. 
Paleozoic seed plants of fern-like aspect; stems short and 
erect, increasing in thickness, bearing compound leaves. 
40. Cycadeae. Cycads. 90 species. 
Sporophyte with erect, woody, simple or little-branched 
stems, bearing compound leaves; vascular bundles collateral 
concentrically arranged, increasing in thickness by their cam¬ 
bium ; cortical meristem developed in which new bundles are pro¬ 
duced; sporophvlls in cones, or the carpels sometimes merely 
in whorls through which the stem grows; ovule with pollen-cham¬ 
ber; female gametophyte becoming large and fleshy; male game- 
tophyte developing two or more large spirally coiled multiciliate 
spermatozoids. 
41. Cordaiteae. Fossil. 
Paleozoic branching trees bearing large, long, thick parallel- 
veined leaves spirally arranged. 
