128 THE PHYSIOLOGY OF STOMATA. 



The contrary explanation, that the moribund tissue prevented the loss of 

 starch from the stomata, would be weakened by the fact that the materials 

 could readily escape into the adjacent epidermal cells. 



The foregoing argument, showing that stomata may be largely independent 

 of photosynthesis, however, does not account for the function of chlorophyll 

 in the guard-cell. According to the theory of von Mohl, the chlorophyll is 

 fundamentally important, and Kohl, following Schwendener and Schellen- 

 berg, has strongly supported this view, having shown the opening of stomata 

 to occur in the regions of the spectrum where the maxima of "assimilation" 

 (photosynthesis) occur. But Darwin has met this argument by pointing out 

 that the opening of stomata in the absence of C0 2 and the persistent occur- 

 rence of starch in the guard-cells do not acccord with the general view which 

 makes the physiology of the chlorenchyma and of the guard-cell identical, 

 though he remarks with real pertinence that "no reason has ever been given 

 for the guard-cells behaving differently to other chlorophyllous tissues." 

 Kohl further (1886, p. 39) speaks of the " Bewegungslosigkeit " of chlorophyll- 

 free stomata, and expresses the belief that the stimulus of light is made effect- 

 ive through the chlorophyll ("dass eine Reizwirkung auf das farblose Plasma 

 der Schliesszellen nicht die Bewegung verursacht, sondern dass das Chloro- 

 phyll die Oeffungsbewegung im Lichte vermittelt"). Kohl's evidence is, how- 

 ever, not convincing. Leitgeb (1888) showed that the stomata in the etiolated 

 petiole of Crambe cordifolia open, though they possess no chlorophyll, and 

 light is completely absent. They were seen, furthermore, to be filled with 

 starch, though this is absent from the tissues. I have confirmed Leitgeb's 

 observations in a species of Brodicea in all points. Arguments which have 

 been based upon observations on the white parts of leaves, assuming that 

 the stomata lack chlorophyll, are negatived by the fact that they do possess 

 this material, in many cases, at least. The stomata on albino shoots of 

 Sequoia sempervirens, however, are said to lack plastids, and it would be of 

 interest to know whether they are motile or not (G. J. Peirce, 1901).* The 

 amount of chlorophyll in the active stomata of different plants, disregarding 

 albinism, is so various, however, that this fact also may well be regarded as 

 throwing doubt on the photosynthetic theory as a complete explanation of 

 stomatal activity. 



In view of the evidence that the guard-cells do behave differently from the 

 chlorophyllous tissues under the same circumstances, f for the support of 



* Since writing this I have had theopportunity of examining some preserved material 

 kindly sent me at the cost of much trouble by Dr. Peirce. I find plastids to be present 

 in the guard -cells, and in shoots exposed to the light; that chlorophyll is formed in the 

 plastids. I infer that the stomata are motile even in white shoots, but this conjecture 

 needs the support of direct observation of the living material. 



tMolisch (1897) observed that, in many plants, the guard-cells and trichomes resist lower 

 freezing temperatures than the remaining epidermal and chlorenchyma cells. And Leitgeb 

 (1888) adduced evidence that the stomata are able to resist higher temperatures and other 



