The term was introduced by G. H. Cady in 1942, to designate plant forms or fossils in coal as distinguished from the material of which the fossils may be composed. Phyterals are identified in general botanical terms that are usually morphological, such as spore coat, sporangium, cuticle, resin, wax, wood substance, bark, etc. The initial composition of the phyterals differed; these or other differences produced during diagenesis may or may not be perpetuated by and during carbonification (coalification). Phyterals are recognized with increasing difficulty in high rank coals. In contrast to macerals which represent a purely petrographical concept, the concept phyteral demands strict correlation with certain organs of the initial plant material.