EFFECTS OF REGIONS OF VISIBLE SPECTRUM 777 



represented the amount transmitted by the red filter. By these means 

 radiation which differed in Hght quaUty but not in total energy, reached 

 the stomata. 



Observations were made on the stomata of the under surface of living 

 leaves of potted plants of Helianthus annuus. The leaves, without being 

 detached from the plant, were clamped lower surface uppermost on a 

 microscope stage. Instead of comparing average measurements on a 

 given number of stomata under each of several different spectral ranges, 

 as previous workers had done, Sierp selected certain stomata for obser- 

 vation and followed the behavior of each stoma as an individual through- 

 out an experiment. This procedure was adopted because of the extreme 

 degree of variability of stomatal behavior not only in different leaves but 

 in the same leaf, under apparently similar conditions. A selected stoma 

 was illuminated for a period of about 4 hr. during the morning of three 

 successive days. On the first and third day the same hght filter was used; 

 on the second day, a different one. Otherwise the stoma was kept in 

 darkness. During the periods of illumination, measurements of the 

 width of stomatal aperture were made at 10-min. intervals by means of an 

 ocular micrometer. These measurements were plotted against time. 



Under these conditions blue, green, yellow, and orange-yellow light 

 of equal intensities were found to be equally effective in causing stomata 

 to open. However, stomata opened much more slowly in red light than 

 in blue light of the same intensity, and the relation of the final width 

 of the openings was as 100:60. Thus, contrary to the conclusions of all 

 previous workers, who had reported either that the red end of the spec- 

 trum was more effective than the blue end or that one region of the 

 visible was as effective as another, Sierp found blue light much more 

 effective than red. On the basis of these results he suggests that the 

 lower rate of transpiration in the red as compared with the blue 

 end of the visible region, as obtained by Iwanoff and Thielmann, might 

 be explained by the failure of the stomata to open as wide in red light as 

 in blue light. 



Sierp, like Sayre (35) and others, also found that stomata remained 

 closed under infra-red radiation. 



ANTHOCYANIN FORMATION IN DIFFERENT PARTS OF THE SPECTRUM 



A relationship between quality of radiation and the development of 

 anthocyanin has been suggested by a number of investigators. In 

 general the blue end of the visible region, the region of the ultra-violet 

 immediately beyond this down to 2900 A, or both have been associated 

 with its formation. The lower limit of effective radiation has never been 

 definitely established, but it may very well be beyond the shortest 

 visible rays. Ultra-violet effects have not as yet been clearly separated 

 from violet and blue visible effects. 



