35 ° Copeland. — The Mechanism of Stomata. 
The first effect of the alcohol is to widen the pore, which 
then gradually closes, the sides becoming apparently straight 
before they meet. The increase in depth at the ends, which 
is partly responsible for opening the pore of this stoma, works 
to better advantage than in the stoma of Osmunda. 
In other Fern stomata, with less thickened ridges, variations 
in depth are responsible for more of the movement. In 
median cross-section the guard-cells are shallower, as well as 
more equally thin-walled. These measurements are of the 
stoma of Aspidium acrostichoides , Swtz. : 
Open. 
Closed. 
Length of stoma .... 
57 
57 
Width of stoma .... 
46-5 
46 
Width of guard-cell 
20 
23 
Width, ridge of entrance . 
4 
3 
Width of pore ..... 
7 (about) 
0 
Width, ridge of exit 
12 
11 
It is noticeable that while the ridge of entrance marked 
the narrowest part of the rift when open, the pore was closed 
by the thin wall inside. In other stomata of the same plant 
the ridges of entrance met one another in closing. And this 
occurs on most of our Ferns, except that the closing is often 
imperfect. In the stoma measured for the last table, the 
change in total width was less than i /a, which may be regarded 
as the share of the Amaryllis type in this case. The stomata 
of some other Ferns — Asplenium montanum , Willd., A.pinnati- 
fidum , Nutt., A. platyneuron , Oakes, and Camptosorus — are 
more slender, and the walls between the adjacent cells strike 
their backs : and the variations in the width of the entire stoma 
are not quite so inconspicuous. Pellaea atropurpurea , Link, on 
the other hand, has stomata of pronounced Medeola type. The 
‘ free ’ situation of the stomata of Niphobolus 1 and some species 
of Aneimia 2 makes no peculiar demands on their mechanism. 
1 K. Giesenhagen, Ueber die Anpassungserscheinungen einiger epiphytischer 
Fame : Schwendener- Festschrift, 1899, P* 1 5 Die Farngattung Niphobolus , Jena, 
1901, p. 85, literature there. 
3 Strasburger, 1 . c. 1866, p. 327 ; F. Hildebrandt, Ueber die Entwickelung der 
