1 84 



HEREDITY AND EVOLUTION IN PLANTS 



casts resulting from the encasement of the organ or 

 organism in the rock-forming material. The tissue itself 

 either decayed or became carbonized, leaving only the 



■■■>•#• 



Fig. 8o. — Fossil incrustations of the foliage of two species of Spheno- 

 phyllum from the coal measures of Missouri. (From U. S. Geological 

 Survey.) 



impression of its surface features. The well-known 

 "fossil fern-leaves," found in coal mines, are of this nature. 

 The tissues of the plant were transformed into coal, 



