52 



THE PHYSIOLOGY OF STOMATA. 



Experiment 166. — July 14-15, 1905 (fig. 16). Ocotillo, with young and mature leaves. 

 In laboratory till 7 h 2o m a. m., July 15, when it was placed in the shade on porch for 

 2 hours, then returned to the laboratory; placed in dark room at io h 2o m a. m. ; 

 temperature 28°C. in laboratory and on porch at 7 n 2o m a. m. 



Table 29. — Rates of transpiration per hour. 



Experiments 163 to 165, inclusive. 



At the end of 16 hours of darkness the rate of transpiration, during a i-hour 

 exposure to light, increased three to four fold, while the increase in the size 

 of the stomata was an average size of 3 micra to 6 micra, i. e., an increase in 

 diffusive capacity of 80 per cent. In three cases a steady rise in the curve is 

 seen after midnight. The stomata of the pieces which had been exposed to 

 prolonged darkness (16 hours), when suddenly exposed to strong midday dif- 

 fused light, responded more rapidly than those exposed earlier in the morning. 



Experiment 166. 



During an exposure from 7 h 2o m a. m. to 9 h 3o m a. m. to relatively strong 

 illumination, the rate of transpiration increased 4.5 times. The average size 

 of the stomata increased from 3 micra to 4 micra (an increased diffusive 

 capacity of about 30 per cent), and thus remained without further change. 



SUDDEN CHANGE FROM DARKNESS TO LIGHT. 



Experiment 115. — June 17, 1905 (fig. 17). Verbena ciliata. Cutting placed in 

 dark room at 3 h 3o m p. m. 



Table 30. — Rates of transpiration per 15 minutes. 



The rate of transpiration in 45 minutes was increased fivefold, while the 

 average transverse dimensions of the stomata increased in 30 minutes from 

 5.5 micra to 7.5 micra, an increase of about 30 per cent. 



