328 Copeland. — The Mechanism of Stomata . 
added (p. 702) : ‘ Diese ungleichformige Wanddicke muss 
auf die Veranderungen dieser Zellen, wenn sie Wasser end- 
osmotisch einsaugen oder abgeben, von Einfluss sein.’ He 
determined that stomata freed from pressure of neighbouring 
cells opened in light and closed in darkness ; but did not 
believe that stomata on uninjured leaves moved likewise by 
their own activity. Passing over Muller’s 1 work, most of 
which has not stood the test of time, the next important 
contribution is Schwendener’s 2 , which described in detail 
the thickening of the walls of several stomata, and showed 
clearly the relation of their structure to their movements : the 
structure being constantly such as to permit an increase in 
turgescence of the guard-cells to open the pore ; and the 
movements of the guard-cells being made more independent 
by thinner parts of the outer wall, next to the guard-cells, 
acting as hinges. 
Leitgeb 3 , as von Mohl had less emphatically done, ascribed 
greater activity to the surrounding, and less to the guard- 
cells ; his view being that if stomata closed at night the guard- 
cells were forced together by the increasing turgescence of 
the subsidiary or epidermal cells. But Leitgeb found stomata 
shut on brightly illuminated plants which had transpired 
freely, when the pressure against the guard-cells was pre- 
sumably not greatest ; and also observed a disappearance of 
solid matter in guard-cells before the pore opened. Schaefer 4 
showed conclusively for certain stomata (Amaryllis, Acomtum , 
&c.) that their movements were independent of the surround- 
ing cells ; for they closed in darkness and remained closed 
even if isolated from other cells ; and opened in a saturated 
atmosphere, when the pressure of the neighbouring cells must 
1 N. J. C. Muller, Die Anatomie und Mechanik der Spaltoffnungen, III. Jahrb. 
f. wiss. Bot., viii (1872), 75-116. 
2 S. Schwendener, Ueber Bau und Mechanik der Spaltoffnungen. Monatsber. d. 
Akad. d. Wiss. zu Berlin, 1881, p. 833. 
3 H. Leitgeb, Beitrage zur Physiologic der Spaltoffnungsapparate. Mitth. Bot. Inst. 
Graz, i (1886), 123-184. 
4 R. Schaefer, Ueber den Einfluss des Turgors der Epidermiszellen auf die 
Function des Spaltoffnungsapparates. Jahrb. f. wiss. Bot., xix. (1888), 178-205. 
Berlin Dissertation. 
