STOMATA DURING WILTING. 



83 



or less apart. In the method of direct observation of the living stomata, the 

 epidermis was removed and mounted under a cover-glass, either in water or 

 not, and a particular stoma was watched under the microscope during a com- 

 plete period of wilting. The objection may be urged that in the separated 

 epidermis the stomata may act differently than when attached to the leaf, 

 but I have offered evidence elsewhere to show that they do not. Besides, 

 the two methods act as mutual checks, and as they comport with one another 

 I feel reasonably certain of my results. 



SELECTED EXPERIMENTS. 



A selected stoma of Verbena was measured and found to be 8 micra wide 

 at i h 5o m p. m. It was watched constantly till 2 h o3 m p. m. The closure was 

 continuous, without any increase in the size of the opening. The epidermis 

 was still moist upon removal from the slide. 



Another instance: 2 h 28 m p. m., 10 micra; 3 h o8 m p. m., o micra; irrigated 

 with water: 3 h o9 m p. m., 4 micra. 



The closures were without previous opening, as I satisfied myself by con- 

 tinual observation. The ease with which stomata take up water is shown 

 by the opening, when irrigated, in 1 minute. No doubt the epidermis as a 

 whole does the same thing, but if the access of water to the stomata upon 

 irrigation had taken place only through the adjoining epidermal cells, we 

 should scarcely expect that the opening would be so rapid. The experiment 

 seems to indicate that the closing of stomata during wilting is the result of 

 a general wilting of the leaf and not an independent reaction of the stomata, 

 and as during the general wilting the concentration of solution of all the 

 cells is gradually raised, it would be difficult to account for the opening of 

 stomata under this condition. The higher degree of concentration within 

 the guard-cells in the morning than in the afternoon, as indicated by the 

 wider condition of the stomata, may possibly be called into account for the 

 greater reactions of stomata in the morning than in the afternoon (as is 

 believed by Darwin to occur), if they occur. I have contributed data on 

 this point under the head of induced rhythm in stomata. 



Table 45. — Closure 0} stomata during wilting. 10 a. m., July, 1906. (Fig. 31.) 



Leaf wilted for — 



i minute . 



2 minutes 



3 minutes 



4 minutes 



5 minutes 



6 minutes 

 8 minutes 



15 minutes 



