1. Exogenites.--Wood formed of regular concentric layers. 2. Endogenites.--Wood composed of insulated bundles of vessels, which are more numerous towards the circumference than at the centre. Class II.--Stems whose internal organization is no longer distinct, but which are characterised by their external form. 3. Culmites.--Stem jointed, smooth; a single impression at each articulation.[94] 4. Calamites.--Stem jointed, regularly striated; impressions rounded, small, numerous, forming a ring round each articulation, or sometimes wanting.[95] 5. Syringodendron.--Stem channelled, not jointed; impressions dot-like or linear, arranged in quincunx.[96] 6. Sigillaria.--Stem channelled, not jointed; impressions in the form of disks, arranged in quincunx. 7. Clathraria.--Stem neither channelled, nor jointed; impressions in the form of rounded disks, disposed in quincunx.[97] 8. Sagenaria.--Stem without joints, or furrows, covered with conical rhomboidal tubercles disposed in quincunx, having at their upper extremity an impression in the form of a disk.[98] 9. Stigmaria.--Stem without joints, or furrows; impressions rounded, distant, disposed in quincunx.[99] [Footnote 94: These stems appear to M. Brongniart to belong to the arborescent grasses, to _Calamus_ or its allied genera.] [Footnote 95: M. de Candolle suggested to M. Brongniart that these stems belong to some plants of the natural order of Equisetaceæ.] [Footnote 96: M. Brongniart considers these remains to belong to genera which are entirely extinct.] [Footnote 97: M. Brongniart shows in his paper the great agreement between these two genera, and the stems of ferns, in every respect excepting magnitude, and considers them as evidently owing their origin to plants of that natural order rather than to the palms.] [Footnote 98: The stems of this genus are referable, in the opinion of M. Brongniart, to those of plants belonging to the family of _Lycopodiaceæ_, notwithstanding the great difference of size between them and those of the recent plants of that natural order.] [Footnote 99: These stems, M. Brongniart supposes, belong rather to plants of the natural order of _Aroideæ_, than to the _Euphorbiaceæ_, or to the Palms to which they have been ascribed by other authors.] FOLIAGE. 10. Lycopodites.--Leaves linear, or setaceous, without ribs, or traversed by a single rib, inserted all round the stem, or in a double row. This genus is subdivided into four sections, as follow:-- _a._ Leaves narrow, lanceolate, inserted in a regular manner all round a stem having the characters of Sagenaria. _b._ Leaves setaceous, inserted in a double row only; stem not reticulated. These he considers as the proper Lycopodites. _c._ Leaves broad, without any apparent ribs, inserted irregularly all round the stem. These differ much from the rest of the genus.