CONCLUSIONS. 125 



eluded that the opening of stomata is not due to the formation of osmotic 

 materials due to photosynthesis. 



I am able to agree with Darwin. Not only this, but if the plant is sub- 

 jected to the experimental conditions at sunrise, before the stomata are open, 

 they open as they would normally. And, vice versa, when they are open, 

 they close as normally. Furthermore, the increase and decrease of starch, 

 and probably oil, go on as in the normally conditioned plant. My conclu- 

 sion is, therefore, that the presence or absence of C0 2 has no direct influence 

 on stomata, and that, physiologically, they are not at all dependent upon 

 photosynthetic processes within the guard-cells. If this be true, the guard- 

 cell is set off as distinct physiologically from the chlorenchyma-cell. Sehel- 

 lenberg's explanation is therefore incorrect, and the whole prevailing theory 

 of the relation of stomatal activity to photosynthesis is thus called into ques- 

 tion. The mere fact that stomata open in the absence of C0 2 shows con- 

 clusively that the movement is not directly connected with photosynthetic 

 activity, even if the process takes place normally in stomata. 



The reduction and increase of starch in the guard-cells, in the absence of 

 carbon dioxid, points rather clearly to the activity of an enzyme, presumably 

 a sort of diastase, as a factor in the mechanism, a view in accord with that 

 of Kohl. 



DISCUSSION AND CONCLUSIONS. 



The facts obtained by experimentation under the above conditions, namely, 

 in air free of carbon dioxid, in total darkness, in red light, and in blue light, 

 accord well with the general theory that photosynthesis, even in stomata, 

 whose plastids are well supplied with chlorophyll, plays a secondary role in 

 their physiology, and is connected only indirectly with their movements (c/. 

 Francis Darwin, 1898, p. 615), and that, therefore, there is a marked quanti- 

 tative difference between the physiology of the typical chlorenchyma-cell 

 and that of the guard-cell. This difference lies in the quantitatively different 

 nature of the plastids. In support of this contention the following arguments 

 may be advanced: 



(1) The formation of starch in the stoma plastids takes place in the dark, 

 and, of course, in the absence of either red or blue light and in the absence 

 of carbon dioxid. In the plastids (chloroplastids) of the chlorenehyma, on 

 the contrary, in accordance with our general understanding, the accumula- 

 tion of starch occurs only when carbon dioxid is available, in white light 

 and in red light.* In Verbena ciliata no accumulation of starch has been 



*Bohm (1874-7) showed that, in seedlings, starch may appear in the ehloroplasts under 

 feeble illumination and in the absence of CO2. The behavior of the ehloroplasts, when 

 starch is available, may under special conditions be very similar to that of the stoma 

 plastids. In the present connection, we find, under the same conditions, a different 

 behavior, which can not be referred to the "isolated/' position of the stomata, since, after 

 all, this isolation is more apparent than real. 



