THE INFLUENCE OF LIGHT UPON THE ACTION OF STOMATA AND ITS RELATION TO THE TRANSPIRATION OF CERTAIN GRAINS

Abstract

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 02 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-