110 THE MEDALS OF CREATION. Cuap. VI. 
and spreads out from the crown, or summit, into an elegant 
canopy. 
The leaves of our branched ferns are persistent, and when 
shed, the markings left by their attachment to the stalk are 
soon obliterated. In the arborescent ferns, on the contrary, 
the petioles become detached from their bases, and fall 
entire, leaving scars or cicatrices on the stem; and these 
impressions are so regularly and symmetrically disposed, 
as to afford characters by which the trunks may be dis- 
tinguished from those of other trees. The stems of the 
tree-ferns are therefore easily recognized in a fossil state 
Lien. 16. PECOPTERIS SILLIMANI; nai. 
Coai Shale. Ohio. 
a. The Stem. 
6. Leaft-stalk, or petiole. 
c. Leaf, or frond, which is bipinnate. 
d. e. Leaflets, or pinnz; the upper, d, are entire; the lower, e, are pinnatifid. 
f. The pinnules, lobes, or segments. 
g. The midrib, or median vein. 
h The veins. The veins are introduced in the leaflets, d; but in the lower 
ones, e, the midribs only are marked. 
externally, by their cylindrical forms without ramification, 
and by the regular disposition and peculiar character of the 
ee ee 
ee oes ee 
