56 



THE PHYSIOLOGY OF STOMATA. 



Experiment 151. — July g, 1905 (fig. 18). Ocotillo. Burette potometer; in dark room. 

 Table 33. — Rates 0} transpiration per hour. 



Time. 



12 day . 



1 p. m 



2 p. m 



3 p. m 



4 p. m 



5 P- m 



6 p. m 



Rate. Width of stomatal pore 



c.c. 

 1.6 

 I.65 

 i-3 

 1 . 1 

 Placed in 

 diffused 

 light. 



3-4 

 2 . 2 

 2.9 



M icra 



2 to 7; mean 4.5. 

 o to 6; mean 3. 



The stomata exposed to diffused light in the mid-afternoon opened in an 

 hour from 3 to 4.5 miera wide, returning to the former dimensions during 

 the succeeding hour. The rate of transpiration rose threefold in 1 hour and 

 fell to two-thirds its rate in the succeeding hour. 



Experiments 48 to 53. — July 16, 1904 (fig. 19). Ocotillo. Vertical tube potometers all 

 placed on porch at 9 p. m. July 16; placed in laboratory at 9 h i5 m a. m. July 17; 

 replaced on porch at io h i5 m a. m. 



Table 34. — Hourly rates of transpiration. 



Time. 



I2 h 45 m a. m 



415 a. m 



6 15 a. m. 



7 15 a. m, 



8 15 a. m 



9 15 a. m 



9 45 a. m 



10 15 a. m 



11 15 a. m 



12 15 p. m 

 5 45 P- m 

 7 30 p. m 



No. 48. No. 49. 



c. c. 



i-7 

 i-7 

 3-5 

 5-7 

 6.8 

 10. o 



7-4 

 4.6 



No. 52. 



Placed in laboratory. 



15.2 8.6 



8.0 6.8 



Replaced on porch. 



3-i 



c. c. 

 1.6 



i-5 



5-o 



8.7 



10.4 



15.0 



10.8 

 8.6 



10.8 



14-3 



7.2 



3-9 



5-6 



3-7 

 4.1 



5-7 

 10.2 



14-5 



11. 4 

 9-4 



10.6 



i3-i 

 10.6 



7-3 



Stomata at 9 h i5 m a. m., 2 to 8 (10) micra; at 9 h 40 m a. m., 2 to 8 micra; at io h 25 m a. m. 

 2 to 8 micra. 



These experiments differ from the preceding only in having been placed 

 in the reduced light of the laboratory instead of in the dark room. The 

 reduction of the rate of transpiration under these circumstances amounted, 

 approximately, to from one-third to one-half (in one case thr< e-fourths), 

 rising again about one-sixth when the stomata were examined. No change 

 was found in their dimensions. 



