On the Movements of Petals 



23 



Light readings also were taken by exposing solio paper to the 

 light to show that the intensity cHd not iniluence opening or clos- 

 ing. Following are some data regarding the amount of light 

 present at the times of opening and closing. If we take the tables 

 jiisu preceding, giving temperature and humidity values, and 

 observe th*e time at which closing occurs in the different situa- 

 tions, and note at the same time the relative light values, light 

 can be seen at once to be of no value in effecting closing, since it 

 is strongest where flowers close earliest. The relative values are 

 obtained by comparing the exposures on solio paper in a photor:- 

 eter, for the different situations, with a sun standard taken at 

 noon on a certain clear day, e. g., March 21, 1905. 



On February 2y, 1905, dandelions were not closed in the green- 

 house at 3:00 P.M. when the relative light value was .05, while 

 out of doors they were two-thirds closed and the light value was 

 .1. At 5:00 P.M., dandelions in the greenhouse were one-third 

 closed with a light value of .02, while out of doors they were 

 entirely closed, and the light was .05. In the stronger light they 

 closed earlier. 



On March i, 1905, open dandelions put out of doors at 9:30 

 A.M. were one-third closed at 10:30 a.m. with a light value of .5, 

 while indoors they were open, and the light was .1. At 4:35 

 p.m., those in the greenhouse were still open, with light at .03, 

 while out of doors they were closed with light at .06. 



On March 6, 1905, at i :30 p.m., the open dandelions put out 

 of doors at 9:00 a.m. were two-thirds or more closed, the light 

 being .15, while indoors at the same time, where the light was .03, 

 they were open as usual. 



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