18 ONOCLEA SENSIBILIS.— SENSITIVE FERN. 
are known as Evolutionists account for the great variations 
between living forms and those which existed in the earlier 
geologic ages. There are other scientific men who regard 
these differences between the early and recent floras as the result 
of sudden geologic or cosmic catastrophes, destroying existing 
forms, and almost contemporaneously succeeding with new 
ones; and who believe that if any did not happen to come 
wholly within the range of these great disturbing influences, 
there would be no reason why a form might not continue without 
material change for countless ages. 
These geological discussions have a peculiar interest in con- 
nection with our present subject, the Sensitive Fern, for its 
remains are found in some very old geological formations in 
which vegetable remains exist, and precisely in the form in 
which we find it now. According to Professor Dawson, of 
Montreal, it was in existence near the Cretacean age, or that 
time in the earth’s history when only reptiles crawled over the 
surface, and the mammalian or sucking animals had not yet 
appeared. In Dr. Dawson’s own language, in his address to 
the Natural History section of the American Association for 
the Advancement of Science, delivered at Detroit in 1875, he 
says: “In a collection of fossil plants from what may be termed 
beds of transition from the Cretaceous to the Tertiary, I find 
among other modern species two recent ferns most curiously 
associated. One is the common Onoclea sensibilis, found now 
very widely over North America, and which in the so-called mio- 
cene times (about the middle of the mammalian era preceding 
man) lived in Europe also. The other is Davatlha tennifolia,.. . 
still abundant on the other side of the Pacific (and Dr. Dawson 
might have added, still growing with the Oxoclea there). These 
little ferns are thus probably older than the Rocky Mountains 
and the Himalayas, and reach back to a time when Mesozoic 
Dinosaurs were becoming extinct, and the earliest Placental 
mammals being introduced. Shall we say that these two ferns, 
and along with them our two species of Hazel and many other 
