346 Copeland . — The Mechanism of Stomata . 
That the mechanism of the Gymnosperm stomata has 
remained so long unexplained is probably due to the difficulty 
of directly observing their movements. Their being over- 
lapped by other cells is less of an obstacle to direct measure- 
ment than the bubble Which persistently clings in the de- 
pression outside the pore, where the waxy surface prevents 
its removal by water. Moreover, on old evergreen leaves the 
walls become so thick even at the £ hinge ’ that movement is 
impossible ; this is the case on the leafless stems of Ephedra. 
The deciduous leaves of Gingko and Larix have motile 
stomata, whose movement can be observed and measured if 
a surface-section is exposed to the light for several hours in 
water from which the gas has been partly driven off, so that 
it will dissolve the air from the outer respiratory chamber. 
They will close in alcohol or glycerine. The widest open 
pore I have observed measured 3-5 //, ; they close completely. 
Measured by focussing from the outer wall of the adjacent 
cell to the dorsal line of the lumen of the guard-cell — from 
x to x in Fig. 27 — the depth of Larix Europaea was found to 
be 15-2^ in water, 19/u ill alcohol. The dorsal wall of the 
guard-cell moved downward at the same time as towards 
the rift in closing. Another stoma changed depth a little more. 
Stomata of similar mechanical structure are not confined 
to the Gymnosperms. It seems to me, as it does to Wester- 
maier ( 1 . c. p. 77), that the stoma of Iris, as it is described by 
Schellenberg (1. c. p. 172), is more like that of a Conifer than 
like that of Helleborus. The stoma of Allium vineale (Figs. 
28-30) is in all essentials — hinges, shape of guard-cells, pitch 
of walls, and distribution of thickening — like that of a 
Conifer : the walls are not so much thickened and not lignified. 
Schwendener figures the stoma of A. Cepa as between this one 
and Amaryllis . In the pitch of the walls, the stoma of 
Polygonatum , described above, approaches the Coniferae. 
The stomata of Botrychium will be described later. 
The grass type is more motile than the Gymnosperm, 
because in it the direction of enlargement of the active ends 
is vertical to the sides of the pore, while the movement in 
