POSITIVE HELIOTROPISM 591 



response-curves the absolute movement, and the rate of such 

 movement. 



I now give a description of the complete apparatus 

 actually used (fig. 241), consisting of the Recorder and the 

 Heliotropic Chamber. In a dark chamber is placed the 

 plant, attached to the Lever as explained before. A portion 

 of the vertical piece with attached mirror, M, projects outside 

 the chamber. It will be seen that by this arrangement the 



Fig. 241. Heliotropic Chamber and Magnetically Controlled | Recorder! 



Heliotropic chamber seen in the middle of the apparatus. Guide-bars to 

 right and left carry sliding lamps, L and i/. Exposure is given by 

 pressing key, k, which raises shutter, s. The corresponding shutter 

 to the right is not shown in the figure. M, mirror of the Optic Lever ; 

 c, controlling magnet. 



plant can be completely protected from light, while its move- 

 ments are at the same time recorded by the spot of light 

 thrown from the mirror, M, upon the recording drum, without 

 the possibility of its reaching the plant within the chamber. 



The chamber carries two projecting graduated arms or 

 guide-bars, one to the right and the other to the left, over 

 which slides the holder for a candle, or incandescent, or 

 Nernst's electric lamp. Li/ ; but if a still stronger light be 



