THE CARBONIFEROUS AND PERMIAN FLORAS. 457 



latter being clearly separated by the absence of a woody 

 envelope, and tlie presence of whorled leaves or branchlets 

 at the articulations of the stem. 



On the other hand, it must be said that extremely strong 

 evidence has been brought forward to show that there is no 

 real distinction between Calamites and Calamodendron, but 

 that the two are simply different states of preservation of 

 the same plant. This view is supported strongly by Pro- 

 fessor Williamson, one of the ablest of living palasobotanists, 

 who holds that the supposed absence of a woody envelope 

 in Calamites is simply due to the fact that in certain speci- 

 mens, and in certain deposits, this structure has been de- 

 stroyed prior to ordinary fossilisation, whereas in others it 

 lias been preserved. Considering how often the internal 

 structure of the Carboniferous plants has been destroyed 

 during mineralisation, and how comparatively seldom it has 

 been retained, there is much to be said for the correctness 

 of this view. 



d. L&pidodendroids. — Under this head we have to con- 

 sider the genera Lepidodendron and Zepidophloios, generally 

 regarded as gigantic extinct members of the Club-moss family 

 {Lycopodiacece). The genus Lepidodendron (fig. 708) com- 

 prises numerous large arborescent plants, which attain their 

 maximum in the Carboniferous period, but which appear to 

 commence in the Upper Silurian, and are well represented 

 in the Devonian. The trunk in some cases reached a length 

 of fifty feet or more, and the branches are given off in a 

 regular, bifurcating manner. The bark is marked with nu- 

 merous rhombic or oval scars, arranged in quincunx order, 

 and indicating the points where leaves were formerly at- 

 tached. The branches were covered with slender, pointed 

 leaves, closely crowded together ; and the fructification was 

 carried at the ends of the branches in the form of cones or 

 spikes. These cones have generally been described under 

 the name of Lepidostroli ; and they consist of a central axis, 

 surrounded by imbricated scales or bracts, each of which sup- 

 ports a sporangium or spore-case. 



In internal structure, Lepidodendron possesses a large cen- 

 tral pith, surrounded by a continuous sheath of scalariform 



