348 Copeland . — The Mechanism of Stomata. 
to quite appreciate the general occurrence among them of the 
mechanical type he was first to explain. 
The stomata of Anthoceros laevis , L., and A. punctatus , L. 
(Figs. 34, 35), have walls of rather uniform thickness, except 
dorsally, where the wall is too thick to be likely to be dis- 
placed by any pressure from the guard-cell. The depth of 
the lumen is equal to the width. I fixed my material without 
examining it fresh, and can only suppose from the structure 
of the stoma that it is inactive. The thin polar areas and 
the absence of hinges make it likely that the width of the 
pore is influenced by the shrinking or swelling of the entire 
sporogonium, with variation in its turgescence. These stomata 
are usually exceptions (Fig. 35) to De Bary’s general rule 1 
that at most the guard-cells are of equal height with the 
epidermal cells. 
The stomata of Botrychium ternatum , Swtz., B. simplex , 
Hitchcock, and B. Lunaria , Swtz., are strikingly like those of 
the Coniferae. B. ternatum has the same form in all sections, 
with the characters a little less extreme. The wall is cellulose ; 
and the outer respiratory chamber is just deep enough to 
make a place for the characteristic hinges. The stomata 
become rigid in autumn. The following measurements were 
obtained on a grown leaf in spring : — 
Open. 
Closed. 
Width of stoma .... 
38 
3 6 
Width of guard-cell 
17 
16-5-17 
Width of pore .... 
4 
^•5 
Length of stoma .... 
55 
55 
At the same time there was the same downward movement 
of the dorsal wall as in the stoma of Larix. In one extreme 
case of a stoma whose pore changed 4 ju, this perpendicular 
movement was 5 \x. These stomata of B. ternatum are 
noticeably straight-backed in surface view ; and those of B. 
simplex are even more so, like the conifer type. B. Lunaria 
rivals many Conifers in the thickness of the walls in median 
cross-section. 
1 Comparative Anatomy, English translation, p. 36 . 
