480 THE PRIMITIVE VEGETATION OF THE EARTH. 
ferous; others are peculiar to the Devonian; and among 
these forms allied to the modern Hymenophyllum and Trich- 
omanes appear to prevail. One remarkable type, C'yclop- 
teris (Archeopteris) Hibernicus, with its American allies, OF 
Jacksoni, etc., extends in the Upper Devonian over both 
continents, yet is wanting in the Carboniferous. Tree ferns 
also existed in the Devonian. Two species have been found 
by Dr. Newberry in Ohio, and remarkable erect trunks have 
been obtained by Professor Hall from Gilboa, in the State 
of New York. The latter are surrounded by aerial roots, 
and thus belong to the genus Psaronius; a genus which, 
however, must be artificial, since in modern tree ferns aerial 
roots often clothe the lower part of the stems while absent 
from the upper part. The only indication as yet of a tree 
fern in the Old World is the Caulopteris Peachii, of Salter, 
from the Old Red of Scotland. It is further remarkable 
that the ferns of the genus Archeopteris are much more 
large and luxuriant in Ireland than in America, and. that 
in both regions they characterize the upper member of the 
system. 
Of the plants of the Paleozoic world, none are more 
mysterious than those known to us by the name Sigillaria, 
and distinguished by the arrangement of their leaves in ver- 
tical series, on stems and branches often ribbed longitudi- 
nally, and by the possession of those remarkable roots 
furnished with rootlets regularly artieulated and spirally 
arranged, the Stigmarie. It seems evident that this group 
of plants included numerous species, differing. from each 
other both in form and structure. Still, as a whole, they. 
present very characteristic forms dissimilar from those of 
their contemporaries, and still more unlike anything now 
living. Ibelieve that many of them were Gymnosperms, 
or at the least, Acrogens with stems as complicated as those 
of Gymnosperms. In the Carboniferous period these plants 
have.a close connection with the occurrence of coal. Nearly 
every bed of this mineral has under it a “Stigmaria under- 
