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 1 p. m. ; burette potometer. 



Table 25. — Rates of transpiration. 



Time. 



Rate. 



c-c. 

 i-4 

 1. 16 

 0.82 

 0.7 

 0.8 

 1 . 2 



2-3 



4.4 

 6.1 

 6.6 



7-4 



Placed in the 



4-2 



30 



2.4 



Placed in the 



3-2 



5-o 



6.0 



7.8 



6.5 

 1 . 1 



Temperature. 



C. 

 25-5 



23 

 23 



26 



28.5 



30 



33-5 



33 



33 



dark. 



3i 



3i 

 light. 



33 



25 



Width of stomatal 

 opening. 



Micra. 



1 to 3 



2 tO 6 (7.5); I tO 2 



o to 4 



3 to 9 



3 to 9 

 2 to 4.5 



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

 being exposed to darkness for 1 hour, remained unchanged. Upon being 

 replaced in the light for the same interval (1 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 1 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 0} transpiration. 



I2 h 04 rl 



1 00 



2 00 



3 00 



3 12 



c. c. 

 22 . 1 

 11. 8 

 150 



p. m 



p. m 



p. m 



p. m. (stomata 2 to 6 micra; 



mean 4) 1 3 . 9 



P- m 5-5 



3 n 22 m p. m 5.0 



3 40 p. m 2.7 



4 00 p. m. (stomata 1 to 5 micra; 



mean 3) 3.3 



500 p. m 12.9 



The transpiration rate was reduced to about one-fourth in 1 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. 



