BITUMINOUS COALS 199 



it is very likely that they are present in an absorbed condition; 

 that is, absorbed by the anthraxylon and other constituents, and 

 so will have lost their identity under the microscope. In the 

 peats, many of these substances may be detected by microchemical 

 means, and are found to be absorbed mostly by the woody constitu- 

 ents, but ordinarily are not visible under the microscope. 



Since there are no, or at the most very few, plant structures 

 remaining in that part of the coal classed under the attritus, the 

 origin of all its constituents, with the exception of the spore- 

 exines, cuticular matter and certain resinous matter, cannot be as 

 closely defined as the anthraxylon matter. Though much of this 

 matter is clearly shown to be woody degradation products, yet 

 it is highly possible that a considerable amount of bark and cortex 

 is included. As has been stated before, bark, that is, that part of 

 the tree or plant usually designated by that term, has not been 

 recognized positively in the coals examined. Cortex, pith, and 

 parenchyma have been recognized comparatively speaking in small 

 quantities. The conifers of the Paleozoic times probably were the 

 only trees with true bark, and the bark of these undoubtedly 

 disintegrated similarly as that of the peat-forming trees and shrubs 

 of the present, and this largely lost its identity and still exists as 

 humic matter. 



The spore-exines. — The spore-exines (Figs. 27-41) are ever- 

 present constituents, and no coal is entirely free from them. Even 

 the coals with the least number of spore-exines, like the Vandalia 

 coal from Indiana, contain a considerable amount of spore 

 matter. Under the microscope, in thin section, they are the most 

 conspicuous objects in the coal, due to their clear yellow color and 

 transparency. In the photographs, representing cross-sections, 

 at a magnification of 200 diameters, they may be recognized as 

 very small Hnear patches (Figs. 19 and 20). At higher magnifica- 

 tions, say at 1,000 diameters (Fig. 21), their true nature is more 

 clearly shown. Here they appear, when whole, as collapsed rings, 

 being in reaHty collapsed spheres, and merely represent the outer 

 shells or spore walls or exines of once living spores of the Paleozoic 

 plants that evidently also contributed to the coal themselves. Its 

 contents, such as nuclei, protoplasm, chloroplasts, and inner spore 



