108 THE PHYSIOLOGY OF STOMATA. 



SUMMARY. 



The chief conclusions to be drawn from the above observations are: 



(i) The starch content of the stomata in the plants studied fluctuates 



between a maximum quantity in the early morning and in the evening and a 



minimum at about 9 to 1 1 a. m. 



(2) Oil is also present (in Verbena) in eomplementarily fluctuating quan- 

 tities, the maximum amount being present at 9 to n a. m., with minimum 

 amounts during the night. 



(3) The stomata open and close rather slowly and maintain a maximum 

 opening for about 3 hours from 9 a. m. to 12 day. This maximum can not 

 be said to be strictly constant, but the differences are but slight and within 

 the personal error of observation. 



Stomatal closure occurs in the early afternoon, advancing steadily till 

 nightfall. It is difficult to correlate this with changes in the surrounding 

 media. 



The disappearance of starch during the earlier part of the day is out of 

 accord with present views of stomatal metabolism. The plastids of the guard- 

 cells have been regarded as strictly photosynthetic (except when non-green), 

 and the movements of stomata have been connected with this process. The 

 above observations have made necessary, therefore, experimentation directed 

 to test the photosynthetic theory, and these are now to be presented. 



RELATION OF STOMATA TO CERTAIN PARTS OF THE SPECTRUM. TO DARKNESS 

 AND TO AIR DEVOID OF CARBON DIOXID. 



In view of the theory enunciated by von Mohl and supported by Schwen- 

 dener and others, that the movements of the stomata are dependent upon 

 the changes in turgor of the guard-cells, and these in turn upon the photo- 

 synthetic activity of the chloroplasts of the guard-cells, the behavior of 

 stomata, and in particular the internal activities of the guard-cells under the 

 conditions implied in the wording of the above caption, are of prime impor- 

 tance. This was recognized by Francis Darwin, who, in 1898, investigated 

 in this field as regards stomatal movement; and his results, together with 

 the earlier ones of Leitgeb (1888), Kohl (1895), and Schellenberg (1896), are 

 those which must be especially noticed in connection with the following data. 



METHOD. 



In carrying out the experiments either cuttings were employed or branches 

 of the experimental plant still attached were inclosed within a large bell-jar, 

 either single-walled or double-walled, or, when it was desired to exclude the 

 light, a good sized "olla," the local Papago Indian water-jar, was used (see 

 plate 5). The interior temperatures were controlled within normal limits by 



