THE CALAMARIEAE 19 



variably, the ridges and furrows of successive internodes 

 are alternate with one another. Many of the specimens 

 taper towards one end, which, as we shall subsequently 

 show, corresponds to the base of the branch (see Fig. 2). 

 Above the nodes we often find more or less circular 

 scars, of relatively large size, which there is reason to 

 believe mark the position of the lateral branches. In 

 well-preserved casts it is usual to find a small circular 

 or elliptical elevation on the surface of each ridge, just 

 below the node (see Fig. 2, Fig. 3, i.e.). In most of these 

 fossils the tissue of the stem enclosing the cast has 

 become reduced to a comparatively thin coaly rind. 

 In a few cases the anatomical structure of the wood 

 and the cast of the pith are preserved in the same 

 stem, 1 and such specimens afford the best evidence for 

 the identification of the two'classes of remains. We will 

 defer a full explanation of the markings on the cast until 

 we have considered the anatomical structure. 



2. The Stem of Calamites. — Petrified specimens of 

 the various parts of plants belonging to the Calamarieae 

 are common in the calcareous nodules of the Lower 

 Coal-measures of Britain and among the silicious 

 remains in the Upper Coal-measures and Permian of 

 France, as well as at other horizons. The anatomical 

 structure of all the organs has thus become known, 

 though the correlation of the fragmentary remains has 

 presented great difficulties. 



We will now go on at once to the anatomical 

 description of the first type to be considered in detail, 



1 See, for example, Williamson, "Organisation of the Fossil Plants of 

 the Coal-measures," Part i., Phil. Trans. Roy. Soc. 1871, Plate xxvi. 

 Fig. 21. 



