1868.] DAWSON — THE COAL FLORA. 371 



cells, as in Sigillaria, and divided into regular wedges by medullary 

 rays, we should find it a continuous cylinder of coarser and finer 

 scalariform vessels. Outside of this, as in Sigillaria, we should 

 have a thick bark, including many tough elongated bast fibres, 

 and protected externally by a hard and durable outer rind. The 

 Lepidodendra were large and graceful trees, and contributed not 

 a little to the accumulation of coal. Several attempts have been 

 made to divide this genus. My own views on the subject are 

 given below. 



Of this genus nineteen species have been recorded as occur- 

 ring 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 forma- 

 tion, Lepidodendra are particularly rare, and L. undulatum is 

 the most common species. In the middle Coal formation, L. ri- 

 mosum, L. dichotomum, L. elegans, and L. Pictoense are prob- 

 ably the most common species ; and L. corrugatum is the charac- 

 teristic Lepidodendron 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 intervening spaces of bark in a perfectly regular 

 manner ; so that in old stems, while widely separated, they still 

 retain their arrangement, while in young stems they are quite 

 close to one another. This is the case in L. corrugatum. 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. undulatum, and generally in those Lepidoden- 

 dra 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 Red 

 Pine of America. In other species the areoles neither increase 

 in size nor become regularly separated by growth of the inter- 

 vening 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 



