OP THE STRUCTURE OF WOOD AND HERBS. 99 



structure of the plants that compose it. Mantell thus remarks : " The 

 slaty coal generally preserves traces of the cellular tissue and spiral vessels ; and 

 dotted cells, indicating the coniferous structure, may readily be detected, by the 

 aid of the microscope, in chips or slices prepared in a proper manner. In many 

 examples the cells are filled with an amber-colored, resinous substance ; in others 

 the organization is so well preserved, that on the surface, exposed by cracking 

 from heat, cellular tissue, spiral vessels, and cells studded with glands, may be 

 detected. Even in the white ashes left after the combustion of coal, traces of 

 the spiral vessels are discernible, with a high magnifying power. Some beds of 

 coal appear to be wholly composed of minute leaves ; for if a mass be recently 

 extracted from the mine and split asunder, the exposed surfaces are found cov- 

 ered with delicate pellicles of carbonized leaves and fibres matted together, and 

 flake after flake may be peeled through a thickness of many inches, and the 

 same structure be still apparent. Rarely are any large trunks and branches ob- 

 servable in the coal, but the appearance is that of an immense deposit of deli- 

 cate foliage." 



