Copeland \ — * The Mechanism of Stomata . 351 
The stomata of Marsilia quadrifolia are very like those of 
Asplenium . Two other Filicineae have stomata too well 
known to be entirely passed over here — Salvinia natans and 
Azolla Caroliniana (Figs. 42, 43). I have had fresh material 
of neither. The stomata of both remain open in formalin and 
alcohol. The mechanism of Azolla has been explained by 
Schaefer (1. c.), with whose material mine agrees in having the 
guard-cells as deep as broad. I agree again with Schaefer, 
Haberlandt (1. c. 1887), and Mettenius that the wall between 
the guard-cells is partly dissolved, which Strasburger 1 denied. 
As to Salvinia , it is agreed even by Kohl (1. c.), who concedes 
so much for no other stoma, that it is rigid. 
The stomata of Lycopodium lucidulum , Mx., and L. com- 
planatum , L., have thickened ridges which give the appearance 
of the Amaryllis type to sections. The dorsal wall, however, 
is thick, so that in surface view the stoma appears surrounded 
by an irregular heavy band — which is not quite so thick in 
Z. obscurum , L. The shape of the lumen, with an observation 
of the movement, shows that the stoma is nearest the type 
of Medeola , but with the activity restricted largely to the 
dorsal half. The stoma measured was of L. lucidulum . 
Open. 
Closed. 
Length 
49 
49 
Width of stoma .... 
5i 
Width of guard-cell, average . 
24 
25 
Width of pore ..... 
3 
1 
Width, between ridges of entrance . 
14 
*3 
The decrease in depth was about 7 \i. These stomata remain 
motile on leaves several years old. I have not found the 
walls lignified (cf. Linsbauer, 1. c.). 
The mechanism of the stoma of Selaginella apus , Spring, 
is similar to that of Lycopodium , though closure is effected 
by the ridge of entrance, as in Dennstaedtia. The stoma of 
Farnkraut-Spaltoffnungen ; Bot. Zeit. xxiv (1866), 245. The mature stoma was 
described by Oudemans in 1865. 
1 E. Strasburger, Ueber Azolla , Jena, 1873, p. 35. 
