BOTANICAL MUSEUM LEAFLETS 
HARVARD UNIVERSITY 
Cab 
e, Massachusetts, June 30, 1939 
Vol. 7, N o. 8 
THE FOSSIL FLORA OF IOWA COAL BALLS 
I. Discovery and Occurrence 
by 
William C. Darrah 
Coal balls are fossiliferous mineral nodules which, 
because they occur occasionally in coal deposits, are of 
special interest to both botanists and geologists. Usually 
these nodular structures are composed of calcite or dol¬ 
omite, more rarely pyrite, but they are always complex 
mixtures of inorganic substances. Well-preserved frag¬ 
ments of plants are often found in coal balls and these 
fossils are the chief source of information concerning the 
anatomy of Carboniferous plants. The plant morpholo¬ 
gist is familiar with a score of extinct plants such as 
Lepidodendron and Calamites which have become funda¬ 
mental to an understanding of our concepts of phylogeny 
and evolution, yet he is prone to overlook the fact that 
we owe our knowledge of them largely to petrifactions 
in coal balls. 
A century has passed since Henry Witham of Lart- 
ington published his Internal Structure of Fossil Vvege¬ 
tables found in the Carboniferous and Oolitic Deposits of 
Great Britain , which although it included notes on only 
twelve species, was the first carefully executed histologi¬ 
cal work on fossil plants. Now the internal morphology 
of more than two hundred Paleozoic plants has been de¬ 
scribed, but not more than twenty of these plants are 
