NORMAL DAILY PERIODICITY. 



41 



A sustained attempt was made by the same method to obtain similar data 

 for Fouquieria splcndcns. Observations were carried on for several days, 

 but upon the examination of the stomata it was found that there had been 

 during the whole period but a small amount of movement, as indicated by the 

 following data: Range of stomatal size, 0-1 to 2-6 micra; range of trans- 

 piration rate, 4.84 grams to 0.2 gram. This was later suspected to be due 

 to the age of the leaves, resulting in the loss, in great measure, of the power 

 of movement by the stomata. The only conclusion to be drawn was that 



— 10/i 



— Sfi 



3 a.m. 



12 



3 p.m. 



12 



— 4 M 



2.JJ. 

 s 



3 a.m. 



Fig. 11. — -Curves of transpiration and stomatal movement for a period of 24 hours, 

 Verbena ciliata, experiment 140. Numerals opposite abscissas on left to be 

 applied to the transpiration curve (<), those on right to curve of stomatal 

 movement (s). 



with an amplitude of stomatal movement no greater than i to 3 micra, the 

 maximum opening being about 4 or 5 micra (in one case only, 6 micra) , there 

 was still maintained a daily rise and fall of transpiration rate, apparently 

 very nearly, if not wholly, normal. The relative immobility of stomata, due 

 to the secondary thickening of their walls, would make them less effective as 

 regulatory organs, and that their functions are not regulatory appears to 

 follow from the progress of transpiration when they are inactive. Though 

 from a different cause, young stomata are also relatively immobile; yet it is 



