The Mechanism of Stomata. 
BY 
EDWIN BINGHAM COPELAND, 
Stanford University , California. 
With Plate XIII. 
T HE movements of stomata have been familiar to 
botanists for more than a century. From all points 
of view, anatomical and physiological, the stomata have 
received more constant and lasting attention probably than 
any other single vegetative structure in the plant. And yet 
recent literature on the subject is most contradictory, not 
only as to the mechanism of their movements, but even as to 
the conditions which influence their opening and closing. On 
the theme proper of this paper— the relation between the 
structure of stomata and their movements — our knowledge 
is incomplete but harmonious, and I am therefore happily 
spared the necessity of controversy. But as this takes for 
granted the occurrence of movement under certain conditions, 
we must first determine what these conditions are, and how, 
aside from the structure of the stomata, the conditions 
are met. 
The earliest attempt at a solution of these problems seems 
to have been that of von Mohl T , who described the thickening 
of the walls of what he regarded as a typical stoma, and 
1 H. v. Mohl, Welche Ursachen bewirken die Erweiterung und Verengung der 
Spaltbffnungen ? Bot. Zeit, xiv (1856), 697, 713. 
[Annals of Botany, Vol. XVI. No. LXII. June, 1902 
