66 



THE PHYSIOLOGY OF STOMATA. 



Only one species, Fouquieria splendens, was used, and while the conclusions 

 drawn may at present be applied solely to this form, the data which support 

 them appear unequivocal. The only apparent source of criticism lies in the 

 fact that the dark room in which the experiments were conducted had to be 

 entered, thereby admitting a little light, and that a candle was used in making 

 the readings. The dark room was, however, entered through another small 

 room, to which but little light was admitted, and further, the experimental 

 room was entered as rapidly as possible. That neither the entrance of a 

 very small amount of light nor the use of the candle vitiated the results would 

 seem clear from the character of the curves derived. Had the light affected 

 the transpiration sensibly it would have been discovered in a repeated positive 

 response, which I failed to detect. This answer is again strengthened by the 

 fact that, as will be seen from the data below, several pieces on different 

 occasions behaved in the same way simultaneously. 



EXPERIMENTS. 



In all experiments cut shoots of Fouquieria splendens set in vertical burette 

 potometers were used. The temperature of the dark room* was controlled 

 within i° C. during the whole period and no appreciable variation of temper- 

 ature took place during the several critical hours, say from 3 a. m. till 9 a.m. 

 The relative humidity was also constant, as indicated by a hair hygrometer 

 (Lamprecht polymeter). 



Experiment 56. — July 18, 1904 (fig. 21). Placed in shade of laboratory porch till 11 p. m., 

 July 18, when it was placed in dark room and there remained till 2 p. m., July 19; 

 then replaced in the light. 



Table 37. — Hourly transpiration rate. 



^Experiments 75 to 79 (p. 71) were not placed in the dark room. 



