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200 FERNS OF NORTH AMERICA.
appear as little whitish scales on the back of the veins. It
occurs in almost all places where the plant is common, is
often produced from root-stocks which bear also normal fronds,
and presents all gradations from the usual sterile frond to the
proper fertile one. Ragiopteris onocleoides of Presl is founded
on a young fertile frond of this species placed with a sterile
one of what Milde judges to be a monstrous form of A sp idiiim
Filix-mas. Maximowicz describes a var. interriipta, from
the Amoor region, in which the fertile frond nearly equals the
sterile, and has elongated pinnæ, with remote segments. This
condition is also sometimes seen in American specimens, and
is hardly a true variety.
In an article on “ The late Extinct Floras of North
America,” which appeared in Vol. ix of the Annals of the New
York Lyceum of Natural History, in April, i868, Professor
Newberry describes certain fossil specimens of ferns occurring
in Miocene argillaceous limestone at Fort Union, Dacotah,
and refers them with little hesitation to this species. I have
not seen the specimens, but, as similar venation and not very
dissimilar fronds are seen in Woodwardia and Pteris, one
may perhaps doubt the absolute certainty of the identification.
Plate L X X II.— Onoclea sensibilis ; a plant from near Boston. Fig.
2 is a fertile pinnule laid open and showing the sori, the sporangia removed'
from one receptacle,, and the indusium from another. Fig. 3 is
a young sorus and its indusium. Fig. 4, a spore. Fig. 5, a portion of
a sterile frond, to show the venation. Fig. 6, section of stipe. Fig. 7,
the var. obiusilobata.
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