§1] 



UPON THE RATE OF GROWTH 



429 



('93) finds that the steins of seedlings of Vicia faba grow 

 behind Sachs' blue solution, which reduces the intensity from 

 one-third to one-half that of daylight, nearly as slowly as in 

 daylight, and much more slowly than in darkness, in the ratio 

 of : daylight, 141 ; blue, 155 ; darkness, 185. Again, Flam- 

 MAEION ('95) cultivated the Sensitive Plant in little conserva- 

 tories behind clear and colored glass.* From a lot of seedlings 

 reared under normal conditions those were selected which were 

 most alike (all 27 mm. high), and placed, July 4th, in the 

 various conservatories. On October 22d the plants had the 

 following average heights : in the red, 420 mm. ; green, 152 

 mm.; white, 100 mm.; blue, 27 mm. (Fig. 122). Thus, under 



Red 



Green 



White 



Blue 



Fig. 122. — Action of different solar rays upon tlie growth of tlie Sensitive Plant. On 

 August 1st, placed as seedlings each 27 mm. high hebind diversely colored glass 

 screens. Photographed Oct. 22. (From Flammarion, '95.) 



* The data concerning methods are as follows : The blue glass used trans- 

 mitted only the more highly refracting rays ; the red was almost strictly mono- 

 chromatic ; the green was less satisfactory, but let through no red. The inten- 

 sity of illumination decreased considerably in the order : white, red, green, 

 blue. The conservatories were placed side by side, under similar conditions, 

 and a current of air was passed through, from one to the other, to maintain a 

 uniform temperature. 



