FIFTY YEARS OF PALEOBOTANY, 1906-1956 593 



chert beds, Aberdeenshire, Scotland. Three genera of petrified plants, Rhynia, 

 Horneophyton, and Aster oxylon, as well as algal and fungous remains, were 

 described by Kidston and Lang (1917-1921). Soon other genera were found 

 and described from western Germany in a series of classic studies by Krausel 

 and Weyland, as well as from Belgium, England, Spitzbergen (Crofts, H0eg, 

 Leclercq, Stockmans), and the United States (Arnold, Banks, Dorf, Goldring). 

 In 1935, true vascular plants, the lycopod Baragwanathia and the psilophyte 



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Fig. 2. Anachoropteris clavata Graham, a coenopterid fern found in coal balls 

 collected near Berryville, Illinois. Cross section of a primary petiole with departing 

 stem trace. Enlarged, X19.5. {Courtesy Wilson N. Stewart. For details see Am. J. 

 Botany 41:192-198, 1954.) 



Yarravia, were described from middle Silurian strata in Australia by Lang and 

 Cookson. 



Most famous among petrified materials are coal balls, known from the Coal 

 Measures (Upper Carboniferous) of England and Pennsylvanian strata in 

 the United States. Although British paleobotanists have been working on 

 these floras for some time, coal balls were first reported in the United States 

 in 1922 and sectioned by Hoskins in the laboratory of the late Professor 

 Noe at the University of Chicago. To date American coal balls have yielded 

 over 150 species of fossil plants, many of them in beautiful state of preserva- 

 tion and described in excellent monographs. 



Carbonized remains, if studied by special methods, also yield spectacular 

 results, particularly in regard to the structure of the cuticle and epidermis. 

 Studies of the cuticles and epidermis of all groups of gymnosperms, living and 

 fossil, have completely altered our concepts of that group. The earlier work 



