124 Fossil Botany. 



with their ends directed outward, imbedded in a looser tissue 

 then it belonged to an aborescent fern. Hereafter will be 

 described the method of preparing slices of fossil wood for 

 investigation by the microscope. If by means of such investi- 

 gation, it is ascertained that the structure is entirely cellular it 

 belonged to the cryptogamia ; if it consist of parallel tubes, and 

 has neither pith nor rays passing from the centre to the circum- 

 ference, it was endogenous ; if any trace be present of tissue 

 crossing the longitudinal tubes at right angles, this will prove 

 the existence of medullary rays, and it must have been exoge- 

 nous ; and if the walls of the tubes are studded with glands 

 (Fig. 5, c.) it belonged to the coniferae. If any vestige of a 

 central pith be discovered, the exogenous nature of the original 

 is undoubted. If the fossil has a distinct bark, it is exogenous 

 if it has merely a rind not separable from the inside, it is 

 monocotyledonous, if neither bark nor rind, cryptogamous. 

 The scars or cicatrices left on the stems by the separation of 

 the leaf-stalks, afford important evidence, as they are often 

 present, even when the trunk is flattened into a thin layer. By 

 these scars the position of the leaves may be ascertained, and 

 the form of the bases ; their probable direction, whether they 

 were opposite, alternate, verticillate, or spirally arranged, 

 deciduous or persistent, imbricated or remote. 



The texture and surface of the leaves are sometimes pre- 

 served in a fossil state, but generally only the outline of the 

 leaf, its division and arrangement, and mode of venation, can 

 be ascertained. The venation or form and distribution of the 

 fibrous parts or veins of the leaf, is a most important character 

 for our guidance, and the following suggestions on this point 

 are offered by Dr. Lindley. If the veins be all parallel, not 

 branched, or only connected by little transverse bars, and the 

 leaves undivided, (see Fig. 10, b,) as in the lily and hyacinth, 

 the plant was probably endogenous ; but if the leaf be divided 

 or pinnated, it may be referrible to the cycadea?. Leaves hav- 

 ing veins of equal, or nearly equal thickness, and forked, or 

 very fine, and simply divided, belong to the fern tribe, the fos- 

 sil genera of which have been constructed principally from the 

 venation. If the veins be of unequal thickness, and reticulated, 

 (see Fig. 12, &,) or arranged in a net-like form, the original was 



