HO THE PHYSIOLOGY OF STOMATA. 



THE RED AND BLUE REGIONS OF THE SPECTRUM. 



The relation of the various parts of the spectrum to stomatal activity has 

 been studied by Kohl (1895) and by Francis Darwin (1898). According to 

 Kohl, the rays between B and C and the rays near F (from F up to the edge of 

 the violet) in the blue are alone effective. In his experiments he used Trianea, 

 the stomata of which opened in the red light between B and C in 9 minutes, 

 completing the opening in 17 minutes, and in the blue light in 7 minutes, 

 completing the movement in 25 minutes. In the yellow- violet, ultra-red, 

 and ultra-violet no movement took place. 



Darwin's results accord with Kohl's so far as the red end of the spectrum 

 is concerned. He failed to find the blue end had any decided effect, but his 

 results are not to be interpreted as militating against Kohl's, for reasons 

 stated by Darwin. 



In carrying forward the following experiments, I have paid attention only 

 to the two ends of the visible spectrum, using bichromate of potash and 

 ammoniacal copper sulphate solution modified by suitable colors, so that, 

 when examined spectroscopically, there was a complete separation of the 

 red and blue ends of the spectrum. The solutions were contained in Sach's 

 double-walled bell-jars. 



RED LIGHT.* 



Experiment 212. — Verbena ciliata, April 24, 1906. Twig remaining attached to the plant 

 arranged under double-walled bell-jar holding modified potassium-bichromate mix- 

 ture. Set up 4 h 30 m a. m., irrigated with water to prevent overheating. 



4 h 3o m a. m., temperature 56 F. Starch absent from chlorenchyma. Present in abun- 

 dance in guard-cells; plastids large and densely staining; separate starch grains scarcely 

 distinguishable; no oil; o to 3 micra (plate 9, fig. 1). 



1 i h 30 m a. m. : Experiment concluded. Maximum temperature during experiment, 93 F. ; 

 air temperature, 8o°. 



Control: Starch in chlorenchyma abundant; starch in guard-cells reduced in amount, 

 though not absent; oil present; 2 to 6, 2 to 8, o to 6 micra (plate 9, fig. 3). 



Experimental part: Starch absent from chlorenchyma. The absence of starch appears 

 to be due to the reduced amount of light contingent on the use of the thick layer of fluid and 

 double glass wall, and not the result of cessation of photosynthesis. Starch is reduced in 

 amount in guard-cells, the plastids lakey and granular with chloral-iodine; occasionally 

 deeply staining, but in these cases the granules of starch are readily distinguishable, o to 8 

 micra (plate 9, fig. 2). 



Experiment 21 4. — Verbena ciliata, April 24, 1906. Conditions as in experiment 212, but 

 begun at n h 30 m a. m., and carried through till 6 h 30 m p. m. 



n h 30 m a. m., control: As in experiment 212 at the same hour (plate 9, fig. 3). 

 6 h 30 m p. m., control: Starch abundant in guard-cells and in chlorenchyma; no oil; 

 o to 2 micra. 



* Between 0.54 and 0.70. 



