266 



PLANT RESPONSE 



electric key, K,, thus closing an electro-magnetic circuit, and 

 so releasing the shutter S, which is immediately in front of 

 the pinhole, by which sunlight is admitted. This drop of the 

 shutter, simultaneously pi^oducing a break of the Ruhmkorff's 

 coil circuit, gives an excitatory electrical shock to the plant. 



Fii". 109. Apparatus for Automatic Record 



When the speed of the drum has become uniform, K., is closed, and the 

 striker, in connection with the drum, closes the electro-magnetic 

 shutter circuit. The dropping of shutter, s, interrupts by K., the primary 

 circuit of the induction coil, the secondary of which gives a shock to 

 the plant. The fall of the leaf pulls down the Optical Lever, o, pro- 

 ducing record on drum. K,, short-circuiting key of secondary. 



The electro- magnetic circuit of the shutter is interrupted 

 by a key, K.,, and this is kept open till the speed of 

 the drum has become uniform. On closing k.^, the circuit 

 is still incomplete ; but the striker, impinging against the 



