DETERMINATION OF THE LATENT PERIOD iii 



acquiring increasing velocity. After this the velocity 

 becomes uniform. If this uniformity should be required 

 throughout the record, the tracing of response may be 

 taken during this later period only. 



The mode of procedure, therefore, is first to make the 

 recording-writer vibrate at its own definite frequency of, 

 say, 100 times per second. The recording-plate is then 

 released and later, when its motion has become uniform, 

 we pass through the pulvinus an electrical stimulus of an 

 instantaneous break-shock. There should be a mark made 

 on the recording-plate corresponding exactly to the moment 

 of stimulation. The horizontal record, consisting of a 

 series of dotted points representing one-hundredth of a 

 second, is suddenly deflected upwards on the initiation 

 of the responsive fall of the leaf. The number of dots 

 intervening between the mark of stimulation and this point 

 gives us the value of the latent period for the specimen. 



Stimulation cannot be effected by hand at any exact 

 predetermined point on the record. This must be done 

 automatically by the moving plate itself. We cannot again 

 give an instantaneous break-shock without previously com- 

 pleting the primary of the Ruhmkorff coil, which causes 

 a disturbing make-shock. 



In order to avoid this the secondary electrodes, during 

 make, should be short-circuited by means of a thick con- 

 ducting-wire ; the secondary shock is thus practically 

 diverted from the plant through the path of least resistance, 

 which is the conducting wire. All these requirements 

 are provided for in practice by the special mechanical 

 devices of the apparatus. 



^Device for Automatic Stimulation 



The essential parts of the automatic arrangement by 

 which a break-shock is given, at a predetermined point on 

 the recording-plate, are shown in fig. 66. 



The recording-plate is allowed to drop by pressing the 



