4 8 



THE PHYSIOLOGY OF STOMATA. 



Experiment 45. Ocotillo, July 14-15, 1904 (fig. 15). Placed in dark room at 12 day 

 and returned to diffused light at i p. m. ; burette potometer. 



TABLE 25. Rales of transpiration. 



The stomata at noon showed measurements of 2 to 6 micra, which, upon 

 being exposed to darkness for i hour, remained unchanged. Upon being 

 replaced in the light for the same interval (i hour), the sizes of the stomata 

 decreased to 2 to 4.5 micra. The change in average transverse dimensions 

 during the second hour was, therefore, from 4 to 3.25 micra. The rate of 

 transpiration was reduced in i hour from 7.4 c. c. per hour to 2.4 c. c. (or 

 to about one-third) and was again advanced to 5 c. c. in one hour, or about 

 twofold. That is, a reduction of about 60 per cent in transpiration rate 

 occurred, with no change in the stomata; and a rise in transpiration of 100 

 per cent occurred in spite of a lowering of the diffusion capacity of the sto- 

 mata in the neighborhood of 40 per cent. 



Experiment 68. Ocotillo, July 20, 1904 (fig. 15). Cutting in potometer; set up at 9 a.m.; 

 placed in dark room for one hour at 3 p. m. ; stomata examined at 3 p. m. and 4 p. m. 

 Measurements in micra. 



TABLE 26. Rates of transpiration. 



1 2 h o4 tn p. m 



1 oo p. m 



2 oo p. m 



3 oo p. m. (stomata 2 to 6 micra; 



mean 4) 



3 12 p. m 



c. c. 



22. I 



ii. 8 



15-0 

 13-9 



5-5 



3 40 



4 oo 



500 



c. c. 



5.0 



2.7 



p. m ....................... 



p. m ................... .... 



p. m. (stomata i to 5 micra; 



mean 3) ---- ............. 3-3 



p. m ....................... 12.9 



The transpiration rate was reduced to about one-fourth in i hour, while the 

 stomata reduced their transverse dimensions to only three-fourths, in the 

 ratios for transpiration of 0.24 and for stomatal diffusion capacity of 0.8. 



