16 L. Lesquereux on the Coal Formations of the United States. 
ers, and fruits, &c., and of which we cannot study the internal 
structure. Or we have isolated vessels transformed into coal or 
pieces of silicified wood of which we can study the internal 
structure only without possibility of comparing it or of referring 
it to external organs so as to know the outward appearance of 
oa vegetable to — my belong.* 
o show at once its most unfavorable and discouraging 
aspect the “difficulty of studying the: shy og! paleontology of 
the coal, we have still to remark that roken, er 
aS: we have 
t. The ee elonttnary simplicity of the flora of the coal and 
aie ‘what number of species that appear to have contributed to 
its formation. All the leaves found in connection with the coal 
have a peculiar and well: marked nervation. In the fossil ferns 
of the coal this nervation is generally well Boies visible and 
characteristic enough for the identification of species. 
In some rare cases where the nervation is ‘early alike for 
different species, each of these may be distinguished by peculiar 
marks, hairs, scales, tubercles or appendages, &c., which permit 
their identification. 
4th. Moreover, one may truly say, that each species even in 
its most different parts has a peculiar look, easily k se at first 
sight by the geet gs oe though indeed indescribable. And 
this is true as well for the leaves of the ferns as for the cicatrices 
which so peculiarly ee the bark of some he 
From this it follows, that the characters on which we have to 
rely for a determination of the fossil plants of the coal are uncer- 
tain, indeed, and of little value for an absolute classification or in 
Brongniart, Hooker, Corda, Géppert and a few other paleontologists have had 
the opportunity of studying through thin, polished sections, the internal structure 
of a few species of fossil wood, and cones from specimens still enaierricie the out- 
' ward form of their bark. They could thus compare the Seated nis se with 
some external characters, che sep pretence of identifying yan S OF € n ge nera 
realtek 
+ Though the number of species of ferns now living is very great, the nervation 
is still considered by some botanists as sufficiently characteristic to separate the 
species of a genus and even of cihenane, (See the opinion of Mittenius in this 
Journal, vol. 31, p. 138). 
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