16 RESEARCHES ON IRRITABILITY OF PLANTS 



variation of the length of the coercer will either bring about 

 full resonance or make it entirely ineffective. When the 

 tuning is nearly but not quite perfect, then we have the 

 phenomenon of beats. In this case, in the successive dots 

 of the record, there will be periodic blanks. For the purpose 

 of exact adjustment of length of the coercer I employ a 

 micrometer-screw, by means of which the most delicate 

 adjustment of length may be carried out. 



For periodic interruption the coercing and vibrating 

 coils may be put in series, but I find it is much easier to 

 obtain a persistent vibration when the coercer coil is placed 

 in a multiple arc with the vibrator coil. An electro-motive 

 force of 4 volts should be sufficient for the purpose of maintain- 

 ing a steady vibration of both the coercer and the vibrator. 



Having thus secured the requisite perfection of the 

 resonating-writer, it is necessary to describe the complete 

 apparatus by which to obtain records of responses in Mimosa 

 and other sensitive plants. For this purpose we require a 

 slide-carrier to hold the recording-plate, and this is to be 

 dropped at a definite speed, without jar ; also the clockwork 

 by which it is to be actuated. Besides these is needed some 

 special means by which the recording-point may be brought 

 to the proper distance from the recording-surface. It is 

 necessary, again, that the response-movement of the writer 

 should be absolutely parallel to the writing-surface, and that 

 its tip or contact-point should be capable of delicate adjust- 

 ment as regards distance. It should be possible, moreover, 

 to bring this writing-point to any position on the recording- 

 surface that may be required. I will now proceed to relate 

 the devices by means of which all these conditions have been 

 met. Some of these will be seen in fig. 3, which illustrates 

 only the upper part of the Resonant Recorder. 



The Slide and Clockwork 



A gunmetal upright, the upper part of which is of trian- 

 gular section, stands on a large disc of the same metal, which 

 is screwed to a larger wooden base-board. The slide-carrier, 



