426 STRUCTURE AND LIFE HISTORIES 



horsetails, and other cryptogams (Figs. 315 and 316). It 

 is instructive in this connection to recall recent careful 

 studies of the structure of coal as seen in transparent 

 sections by the aid of the microscope. These sections, 

 prepared by Professor Jeffrey, reveal the remarkable fact 

 that the soft, or bituminous, coals contain carbonized 

 remains of innumerable spores of the plants which con- 

 stituted the dominant vegetation during the geological 



FIG. 317. Photomicrograph of a thin section of cannel coal from 

 Kentucky, formed under open-water conditions, i.e.^ of the muck at the 

 bottom of ancient lakes or lagoons. The light, roundish bodies are spores. 

 (Cf. Figs. 315 and 316.) (After E. C. Jeffrey.) 



period (Carboniferous), when coal was being formed (Fig. 

 317). Such studies necessitate a radical change in our 

 earlier conception as to the conditions and method of 

 coal-formation. 



These facts also illustrate how the study of what might, 

 at first thought, seem insignificant, impractical, or unim- 

 portant, and not closely related to our daily lives, may, 

 at any time, furnish the key to unlock the mystery of 



