1865.] DA^YSON— COAL-FOEMATIOK. 137 



9. Lepidodendron. — Of this genus nineteen species have been re- 

 corded as occurring in the Carboniferous rocks of Nova Scotia. Of 

 these, six occur at the Joggins, where specimens of this genus are very- 

 much less abundant than those of Sigillaria. In the newer Coal- 

 formation Lepidodendra are particularly rare, and L. undidatum is 

 the most common species. In the Middle Coal-formation L. rimo- 

 sum, L. dichotomum, L. elegans, and L. Pictoense are probably the 

 most common species ; and L. corrugatum is the characteristic Lepi- 

 dodeQidron of the Lower Carboniferous, in which plants of this species 

 seem to be more abundant than any other vegetable remains whatever. 



To the natural history of this well-known genus I have little to 

 add, except in relation to the changes which take place in its trunk 

 in the process of growth, and the study of which is important in 

 order to prevent the undue multiplication of species. These are of 

 three kinds. In some species the areoles, at first close together, 

 become, in the process of the expansion of the stem, separated by in- 

 tervening spaces of bark in a perfectly regular manner ; so that in 

 old stems, while widely separated, they still retain their arrange- 

 ment, while in young stems they are quite close to one another. 

 This is the case in L. corrugatum (PI. XI.). In other species the 

 leaf-scars or areoles increase in size in the old stems, still retaining 

 their forms and their contiguity to each other. This is the case in 

 L. undidatum, and generally in those Lepidodendra which have very 

 large areoles. In these species the continued vitality of the bark is 

 shown by the occasional production of lateral strobiles on large 

 branches, in the manner of the modern Eed Pine of America. In 

 other species the areoles neither increase in size nor become regularly 

 separated by growth of the intervening bark ; but in old stems the 

 bark splits into deep furrows, between which may be seen portions 

 of bark still retaining the areoles in their original dimensions and 

 arrangement. This is the case with L. Pictoense. This cracking of 

 the bark no doubt occurs in very old trunks of the first two types, 

 but not at all to the same extent. I figure three examples of these 

 peculiarities in mode of growth : — 



Lepidodendron corrugatum, Dawson. — I quote in the Appendix 

 my description of this species, and may refer to the figures in Plate 

 XL for further illustration. I do not know any other species in 

 Nova Scotia which has the same habit of growth ; but L. ocidatmn 

 and L. distans of Lesquereux show a tendency to it. The present 

 species is exclusively Lower Carboniferous, and occurs on that 

 horizon in ISTew Brunswick, in Pennsylvania, and, I believe, also in 

 Ohio ; though the beds holding it in the latter State have been by 

 some regarded as Devonian. 



L. undidatum, Sternberg. — I think it not improbable that several 

 closely alhed species are included under this name. On the other 

 hand, all the large-areoled Lepidodendra figured in the books must 

 have branches with small scars, which, in the present state of know- 

 ledge, it is impossible to identify with this species. I suppose that L. 

 elegans resembles the present species in its mode of growth, at least 

 if the large-scarred specimens attributed to it are really of the same 



