STOMATAL RESPONSE TO SUDDEN CHANGE. 45 



a large diffusion capacity. Considerations of this sort make it extremely diffi- 

 cult to account for the course of transpiration in Livingston's experiments by 

 stomatal movement. 



There appears to be, therefore, warrant for the view that if such fluctuations 

 occur in the rate of transpiration, unaccompanied by corresponding changes 

 in the dimensions of the stomata, the regulatory function is almost nil. The 

 following experiments are presented as affording data on this point. 



RESPONSES IN TRANSPIRATION AND IN STOMATAL MOVEMENT TO SUDDEN 

 CHANGES IN ILLUMINATION. 



EXPERIMENTS. 

 The following experiments were designed to determine (a) whether an 

 induced rhythm in transpiration can be shown to exist, and (b) whether sudden 

 changes in the rate of transpiration resulting from the removal of the plant 

 from light to darkness, or vice versa, are accompanied by stomatal movements 

 which may be regarded as quantitatively correlated. The latter we have 

 under immediate consideration, the question of induced rhythm being treated 

 at page 64. The experiments are roughly classified for convenience, accord- 

 ing to the change, whether from light to darkness, or vice versa, but can not 

 be completely segregated. 



LIGHT TO DARKNESS. 

 Experiments 172-179. Ocotillo. July 18-19, 1905. (Fig. 13.) 



Eight cuttings were adjusted to burettes, and after standing for an hour or 

 more they were paired off and readings were begun. One pair of cuttings 

 was confined to the dark room permanently; another pair was confined to 

 the dark room for 17 hours and then placed in diffused light on the porch 

 of the laboratory; a third pair was placed upon the porch, but protected 

 from direct sunlight during the day; the fourth pair remained under similar 

 conditions, except that it was placed in the dark room for an hour. Rates 

 are cubic centimeters per hour. 



Aside from the first few hours the deportment of the plants was remarkably 

 uniform, the rise and fall in rate in successive periods being the same for all, 

 with few exceptions. To be noted are the maxima at 4 a. m. (174, 176-179) 

 and 9 a. m. (Nos. 173-174, 176-179), aside from the great day maximum at 1 1 

 a. m. The absence of a maximum in the curves of the plants kept in the 

 dark at the time when it normally occurs (1 1 a. m.) is also to be noted. Nos. 

 172 to 175 show each a distinct maximum at 4 to 7 a. m. and this behavior 

 may be compared with that of the other pieces (Nos. 176 to 179) which pro- 

 duced each a maximum at 4 a. m. 



After a prolonged exposure to darkness, the plants exposed to moderate 

 illumination increased their rate of transpiration in the ratios 6.25 (174) 

 and 3.5 (175) rising to nearly the normal rate for the particular hour. Con- 



