12 



THE PHYSIOLOGY OF STOMATA. 



An examination of the plastids, even when they are devoid of starch, fails 

 to convince one that chlorophyll is present. I am inclined to believe that 

 they are not chlorophyll-bearing, and it turns out that Kohl (1886, p. 39) 

 sought for and believed that he found chlorophyll-free or chlorophyll-poor 

 stomata on the corolla-like calyx leaves of the verbenaceous Chlorodendron 

 half our i and in the white portions of variegated leaves of Euonymus japonicus 

 and the grass pits menus imbecillis. Certainly the stomata of Verbena ciliata 

 are chlorophyll-poor, if this substance be not, indeed, absent ; but I have not 

 found, as Kohl reports for the species above named, that stomatal activity is 

 correlated with the absence or presence of chlorophyll. Further reference to 

 this point will be made. 



Fig. 5.— Variation of form taken by pore of Verbena ciliata during opening. The widest measured 

 10 micra broad. All dimensions of drawings are in proportion. X 2450. 



The distribution of stomata per unit area of leaf for Verbena ciliata has been 

 given in table 2. Their size and the changes in dimensions undergone during 

 plasmolysis are indicated in table 3. 



Table 3. — Range 0} size 0} stomata on the same leaf. 



Small stomata can open nearly as widely as large ones, though the length 

 of the pore may vary very considerably. 



The degree of mobility exhibited by these organs is indicated by the figures 

 in tables 4 to 6. 



It is quite evident from the measurements in these tables that, in spite of 

 the very small amount of chlorophyll present, if indeed it is present, the 

 stoma of this plant is by no means immobile or, as shown by certain of the 

 data to be presented later, slow to react. 



