Copeland , — The Mechanism of Stomata. 331 
causing the pore to close. The turgescence of the subsidiary 
and other epidermal cells must vary, but there is no reason to 
suspect that their turgor does so, except inappreciably with 
the temperature. 
To distinguish between the entire opening between the 
guard-cells and the narrowest part of this opening, where it 
closes, I have decided, reluctantly, to call the former the rift, 
and the latter the pore. To use ‘pore’ for one and ‘pore 
proper * for the other is quite unsatisfactory. e Centralspalte ’ 
serves for the pore, when it is central, but it forced Haber- 
landt 1 to the negative description of the stoma of Poly- 
trichum as ‘ohne Centralspalte/ and no English word will 
translate it. 
Hinges in the outer wall, next the guard-cell, were recog- 
nized by Schwendener (1881) as necessary to permit the 
lateral movement of the guard-cell. A similar thin line on 
the inner wall is called an inner hinge (Haberlandt, 1887). 
Besides these lateral hinges, which may extend a part or the 
whole of the side of the guard-cell, Westermaier 2 recognizes 
similar thin places at the ends as polar hinges. In all of 
these places it is most necessary, from the mechanical stand- 
point, to distinguish between mere thin lines, which will bend 
but not give way, and therefore are fixed axes of revolution — 
real hinges — and broad bands of thin wall, often the entire 
wall of the subsidiary cells, which permit movement by the 
guard-cells, but which are not fixed axes deserving to be 
called hinges at all. The difference in the movements 
permitted by the hinge and by the thin band is obvious. 
More details as to the hinges and their relation to the 
mechanism of stomata will accompany the treatment of the 
stomata themselves. 
The pressure that may be exerted against stomata is of 
two very different kinds. That of the neighbouring cells, 
1 G. Haberlandt, Beitrage zur Anatomie und Physiologie der Laubmoose. 
Jahrb. f. wiss. Bot., xvii (1886), 359-498. 
2 Max Westermaier, Ueber Spaltoffnungen und ihre Nebenapparate. Schwendener 
Festschrift, 1889, p. 63-80. 
