AMERICAN 
JOURNAL OF BOTANY 
Vol. VI 
April, 1919 
No. 4 
THE INFLUENCE OF LIGHT UPON THE ACTION OF STO- 
MATA AND ITS RELATION TO THE TRANSPIRATION OF 
The stomata of leaves are the passages through which the necessary 
exchange of gases takes place between the interior of the land plant and its 
leaves and the outside world. They are the organs through which CO2 
and O2 are taken from the air and given back to it. And it is through them 
that water vapor passes out into the air. The stomata are the exterior 
openings of intercellular spaces which may extend for great distances in the 
body of the plant. These openings are bounded by paired guard cells 
possessing in most plants a markedly greater degree of elasticity than the 
other epidermal cells. The mechanism and the behavior of stomata have 
been the object of study of many botanists for decades. For the older 
literature of the subject one may refer to Pfeffer (i). Only the few more 
recent papers bearing on the specific question which we asked ourselves 
will be referred to here. 
In general the behavior of the stomata of the Gramineae is as follows. 
When the opposite ends of the guard cells of a pair are in contact with each 
other the stoma is thereby closed. These opposed ends are thin-walled, 
the rest of the wall being thick and stiff. Opening begins with the expansion 
of the guard cells. This results in the separation of the guard cells, at first 
at the ends of the stoma, and later in the middle as well, the guard cells 
straightening and giving to the pore its familiar oblong shape and its uniform 
width for nearly its whole extent. Closing appears to be the reverse of 
this process. This action of the guard cells seems to be a mechanical 
process dependent upon the character of the environment in which the 
plant lives. 
The times, conditions, and significance of the opening and closing of 
stomata have interested many plant physiologists, and there are certain 
general conceptions current, as indicated by the concise statements of the 
textbooks. But the work of one of us in the field, in which the possible 
effect of sulphur dioxide fumes upon the stomata, as well as upon the other 
cells of the leaf, became a matter of importance, made it necessary to ascer- 
CERTAIN GRAINS 
John Gray and George J. Peirce 
[The Journal for March (6: 87-130) was issued March 28, 1919.] 
131 
