Dr. J. W. Dawson on Spore-cases in Coals. 327 



bituminous coal. They are also very little liable to decay, and 

 they resist more than other vegetable matters aqueous inhltra- 

 tion — properties which have caused them to remain unchanged 

 and to resist the penetration of mineral substances more than 

 other vegetable tissues. These qualities are well seen in the 

 bark of our American white birch. It is no wonder that ma- 

 terials 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 Sigillariai and 

 similar trees, just as any single flattened trunk imbedded 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 tissues, not 

 only from the fruits and spore-cases of plants, but also from 

 their leaves and stems. The same considerations impress us, 

 just as much as the abmidance of spore-cases, with the im- 

 mense aniount 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 following very 

 valuable information, which at once places in a clear and pre- 

 cise 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 carbonaceous mat- 

 ter, to which the name of suherin has been given. The spores 

 oILycopodium also approach to this substance in composition, 

 as will be seen by the following, 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 suher^ from which the ash and 2*5 per cent, of cellu- 

 lose have been deductedf. 



Cellulose. Cork. Lvcopodium. 



Carbon 44-44 65-73 ' 64-80 



Hydrogen 6-17 8-33 8-73 



Nitrogen 1-50 6-18 



Oxygen 49-89 24-44 20-29 



100-00 100-00 100-00 



" This difference is not less striking when we reduce the 

 above centesimal analyses to correspond with the formula of 



* Liebig & Kopp, Jahrbuch, 1847-48. f CTinelin, Ilandb. xv. 145. 



