VEGETATION OF THE COAL PERIOD. 
421 
Ferns. —We are struck at the first glance with the similar¬ 
ity of the ferns to those now living. In the fossil genus Pe- 
copteris^ for example (Fig. 448), it is not easy to decide wheth¬ 
er the fossils might not be referred to the same genera as 
those established for living ferns; whereas, in regard to some 
of the other contemporary families of plants, with the excep¬ 
tion of the fir tribe, it is not easy to guess even the class to 
which they belong. The ferns of the Carboniferous period 
are generally without organs of fructification, but in the few 
instances in which these do occur in a fit state for microscop¬ 
ical investigations they agree with those of the living ferns. 
When collecting fossil specimens from the coal-measures 
of Frostburg, in Maryland, I found in the iron-shales several 
species with well-preserved rounded spots or marks of the 
sori (see Fig. 448). In the general absence of such charac¬ 
ters they have been divided into genera distinguished chiefly 
Ficr. 44S. Fig. 4i0. 
Pecopferis elliptica^ Bunbnry.* Frostburg. Caulopterisprimceva^ Liudley. 
by the branching of the fronds and the way in which the 
A'eins of the leaves are disposed. The larger portion are 
supposed to have been of the size of ordinary European ferns, 
but some were decidedly arborescent, especially the group 
called Caulopteris (see Fig. 449) by Lindley, and the Psaro- 
nius of the upper or newest coal-measures, before alluded to 
(p. 393). All the recent tree-ferns belong to one tribe {Poly- 
podiacem)^ and to a small number only of genera in that 
tribe, in which the surface of the trunk is marked with scars, 
* Sir C. Bunbury, Quart. Geol. Journ., vol. ii. 1845. 
