256 
THE SENSITIVE AND OSTRICH FERNS. 
where this author obtained his specimens. In the fourth 
edition of Amos Eaton’s botany published in 1834, the 
author says: ‘ The leaflets slowly ap- 
proach each other on squeezing the stem 
in the hand.”” Many observers will testify 
that they cannot be made to dosoin these 
degenerate days. The species is some- 
times called oak fern or oak-leaved fern. 
In some ancient botanical works it is 
mentioned as “ dragon’s bridges,” though 
for what reason, no one seems to know. 
The sensitive fern is abundant in nearly 
all the territory from Canada to the Gulf 
of Mexico and west to the Mississippi. 
Scattered colonies occur as far west as 
Wyoming, and the same species is again noticed in 
Japan. In Montana, this species, or one exceed- 
ingly like it, has been found as a fossil. 
Growing with normal fronds, there is often 
found a form half-way between fertile and sterile, 
It was once considered to be a permanent type 
and given the varietal name of obtusilobata, but it 
is now known to be due merely to the destruction 
of the early sterile fronds. It usually contains 
less leaf surface than the ordinary sterile frond 
and in cutting resembles the twice pinnate fertile 
one. Commonly it bears a few abortive sori, all 
of which show it to be a partially transformed 
fertile frond. Prof. Geo. F. Atkinson, who made 
extensive experiments with this plant, found 
that he was able to produce the variety at will, by 
\ Onoctea sensisitis iMPly cutting off the early sterile fronds, 
obtustlobata, 
