336 Copeland. — The Mechanism of Stomata. 
to stomata of fixed outline. Solereder 1 describes what I 
take for a similar peculiarity of the wall of Erodium cicutarium 
and Geranium Londesii , figuring the latter. On California 
material of E. cicutarium however I find no such structure. 
The stomata of Pyrola secunda , L., bear a superficial resem- 
blance, but the mechanism is altogether different. Linsbauer 2 
describes and figures what seems to be the same structure on 
Lycopodium complanatum , L., var. thyoides , H. B. K. It is 
not present on our American L. complanatum , the dorsal 
wall of whose guard cells is too thick to require reinforcement. 
Leitgeb ( 1 . c.) describes projections from the wall into the 
lumen of the guard-cell, of Galtonia and some other plants. 
It may be of interest to add to this account of the stoma of 
Medeola that while only a part of the guard-cells show plas- 
molysis in 4 per cent. KN 0 3 (tested during day), the pore 
begins to narrow in 1 per cent., and in 1-5 per cent, closes 
entirely if it does so at all. 
The nearest approach to the stoma of Medeola hitherto 
described is that of 
Mnium cuspidatum, 
made familiar by Haberlandt 3 . The Mnium stoma approxi- 
mates mechanically that of Medeola , agreeing in that the 
total area is constant, the pore opening with an increase in 
the depth of the guard-cells : but it falls short of the type, as 
Haberlandt’s measurements and diagram show, in that the 
outer (upper) wall is rigid, so that the width of the anterior 
vestibule is fixed, the movement being executed entirely by 
the ventral and inner walls. 
The stoma of 
FUN ARIA HYGROMETRICA 
differs from that of Medeola to the same extent as does that 
of Mnium , but in this case the inner wall is rigid (Fig. 3), 
1 H. Solereder, Systematische Anatomie d. Dicotyledonen. Stuttg., 1 898-9, p. 193. 
3 K. Linsbauer, Beitrage zur vergleichenden Anatomie einiger tropischen Lyco- 
podien. Sitzungsber. d. k. Acad. d. Wiss. Wien, cvii. i (1898), 995. 
* L. c., 1886: Physiol. Pflanzenanat., 2nd ed., p. 390. 
