94 



A MONTANE RAIN-FOREST. 



In the second experiment there is a sharp break in the morning rise 

 of the evaporation curve, accompanied by a lessening in the rate of 

 increase of transpiration. These checks are accompanied by a fall in the 

 relative transpiration, which then continues to rise throughout the re- 

 mainder of the day. The fall in relative transpiration at noon is accepted 

 by a fall in stomatal openness, giving the curves of relative transpi- 

 ration and stomatal movement 

 a good agreement for the day. 



In an experiment with Pilea 

 nigrescens (table 37, fig. 16) 

 which was performed along 

 with the first one on Peperomia 

 turfosa, already described, and 

 was discontinued at 2 p. m., w f e 

 have a gradual rise in stomatal 

 openness until 2 p. m., together 

 with a rise in the relative tran- 

 spiration up to 12 noon, and a 

 slight fall thereafter. The shape 

 of the curves of rise for the two 

 are unlike, and between 12 and 

 2 p. m. there is the slight fall of 

 relative rate in spite of a con- 

 tinued increase of the stomata. 

 The increase of stomatal open- 

 ness between 12 and 2 p. m. was 

 greater, in fact, than that be- 

 tween 8 and 10 a. m., but in 

 the latter case there w r as a 

 sharp rise in the relative rate, accompanying a rapid rise of evapora- 

 tion. The 6 a. m. readings of evaporation and transpiration in this 



Table 36. Transpiration, relative transpiration, and stomatal behavior in Peperomia turfosa. 



Series run in laboratory; transpiration by weighing method; stomata from potted 

 plants under same conditions as those weighed. 



Fig. 16. Graphs for evaporation ( :). and for 

 transpiration (T), relative transpiration (p), 



E 



and stomatal area (S) of Pilca nigrescens. 



