RESPONSIVE CURVATURES — NEGATIVE GEOTROPISM 505 



experiment was performed with a long flower-scape of 

 Uriclis Lily laid horizontally. The attachment to the re- 

 cording lever was made with the upper end of the specimen, 

 the lower end being held in a clamp. The specimen was 

 30 cm. long, and the responsive movement was found to be 

 •23 mm. per minute (fig. 211). Here, too, ice-cold water was 

 applied to the upper and lower surfaces alternately, four 

 times in succession, and it will be seen from the figure that 

 an application of cold to the upper surface caused arrest of 



Fig. 211. Effect on Apogeotropic Movement of Temporary Applications 

 . of Cold alternately to Upper ( | ) and Lower ( f ) Surfaces of Horizontally 

 laid Scape of Uriclis Lily 



Application above is seen to produce arrest of movement, while application 

 below has no perceptible effect. 



the responsive movement, while a similar application below 

 produced no effect that could be detected. 



These experiments conclusively prove that the funda- 

 mental responsive effect induced by stimulus of gravitation 

 is not acceleration, but contraction, or retardation of growth, 

 precisely similar to the action of other forms of stimulus. 



Though, under cooling, there cannot be any exhibition of 

 mechanical response to gravitation, yet it appears that the 

 effect of gravitation may be held latent in the organ, as will 



