1870.] DAWSON — SPORE-CASES IN COAL. 375 



to. Such epidermal and cortical substances are extremely rich in 

 carbon and hydrogen; in this resembliug bituminous coal. They 

 are also very little liable to decay, and they resist more than other 

 vegetable matters aqueous infiltration ; 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 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 

 Sigillariae 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 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 following 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 carbona- 

 ceous matter, to which the name o^ suherin has been given. The 

 spores of Lycopodium also approach to this substance in composi- 

 tion, as will be seen by the following, one of two anal3^ses by 

 Duconi,'-^ along with which I give the theoretical composition of 

 pure cellulose or woody fibre, according to Payen and Mitscher- 

 jich, and an analysis of the suberin of Cork from Quercus suher, 

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

 deducted. t 



*Liebig and Kopp, Jahresbuch, 1847-48. 

 t Gmelin, Handbook, xv. 145. 



