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 producing a break of the Ruhmkorff's 

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



FlQ. 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 3 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. 2 , 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 



