In older stems three modes of growth are observed. In some species the expansion of the bark obliterates the leaf-bases and causes the leaf-scars to appear separated by wide spaces of more or less wrinkled bark, which at length becomes longitudinally furrowed and simulates the ribbed character of Sigillaria. In others the leaf-bases grow in size as the trunk expands, so that even in large trunks they are contiguous though much larger than those on the branches. In others the outer bark, hardening at an early age, is incapable of either of the above changes, and merely becomes cleft into deep furrows in the old trunks. _Lepidophloios._--Leaf-bases transverse and prominent--often very much so. Leaf-scars transversely rhombic or oval with three vascular scars, the central largest. Leaves very long and one-nerved. Large strobiles or branchlets borne in two ranks or spirally on the sides of the stem, and leaving large, round scars (_cone-scars_), often with radiating impressions of the basal row of scales. Species with long or drooping leaf-bases have been included in _Lepidophloios_ and _Lomatophloios_, Species with short leaf-bases and cone-scars in two rows have been called _Ulodendron_, and some of them have been included in Sigillaria (sub-genus _Clathraria_). Decorticated stems are Bothrodendron and _Halonia_. Some of the species approach near to the last genus, especially to the Lepidodendra with rhombic leaf-bases like _L. tetragonum_. _Cyclostigma._--Leaf-bases undeveloped. Leaf-scars circular or horseshoe-shaped, small, with a central vascular scar. In old trunks of Cyclostigma the leaf-scars become widely separated, and sometimes appear in vertical rows. Young branches of Lepidodendron sometimes have the leaf-scars similar to those of Cyclostigma. _Leptophleum._--Leaf-bases flat, rhombic; leaf-scars obsolete; vascular scar single, central. The last two genera are characteristically Devonian. In contradistinction from the trees above mentioned, the following general statements may be made respecting other groups: In conifers the leaf-bases are usually elongated vertically, often scaly in appearance, and with the leaf-scar terminal and round, oval, or rhombic, and with a single well-marked vascular scar. In Calamites, Calamodendron, and Asterophyllites the scars of the branchlets or leaves are circular or oval, with only a single vascular scar, and situated in verticils at the top of well-marked nodes of the stem.