THE CARBONIFEROUS FLORA. 



143 



materials of this kind should constitute considerable 

 portions of such vegetable accumulations as the beds of 

 coal, and that when present in large proportion they 

 should afford richly bituminous beds. All this agrees 

 with the fact, apparent on examination of the common 

 coal, that the greater number of its purest layers consist 

 of the flattened bark of Sigillarice and similar trees, just 

 as any single flattened trunk embedded in shale becomes 

 a layer of pure coal. It also agrees with the fact that 

 other layers of coal, and also the cannels and earthy 

 bitumens, appear under the microscope to consist of 

 finely comminuted particles, principally of epidermal tis- 

 sues, not only from the fruits and spore-cases of plants, 

 but also from their leaves and stems. These considera- 

 tions impress us, just as much as the abundance of spore- 

 cases, with the immense amount of the vegetable matter 

 which has perished during the accumulation of coal, in 

 comparison with that which has been preserved. 



I am indebted to Dr. T. Sterry Hunt for the fol- 

 lowing very valuable information, which at once places 

 in a clear and precise light the chemical relations of 

 epidermal tissue and spores with coal. Dr. Hunt says : 

 "The outer bark of the cork-tree, and the cuticle of 

 many if not all other plants, consists of a highly car- 

 bonaceous matter, to which the name of suberin has been 

 given. The spores of Lycopodium also approach to this 

 substance in composition, as will be seen by the follow- 

 ing, one of two analyses by Duconi,* along with which 

 I give the theoretical composition of pure cellulose or 

 woody fibre, according to Payen and Mitscherlich, and 

 an analysis of the suberin of cork, from Quercus suber, 

 from which the ash and 2*5 per cent of cellulose have 

 been deducted, f 



* Liebig and Kopp, " Jahresbuch," 1847-48. 

 f Gmelin, " Handbook,'' xv., 145. 



