I may here say a few words of the manner in which the period of transmission can be found from the record given by my Resonant Recorder, fully described in my previous paper. The writer attached to the recording lever of this instrument is maintained by electromagnetic means in a state of to-and-fro vibration. The record thus consists of a series of dots made by the tapping writer, which is tuned to vibrate at a definite rate, say, 10 times per second. In a particular case whose record is given in Curve 1 (Fig. 46), indirect stimulus of electric shock was applied at a distance of 15 mm. from the responding pulvinus. There are 15 intervening dots between the moment of application of stimulus and the beginning of response; the time-interval is therefore 1.5 seconds. The latent period of the motile pulvinus is obtained from a record of direct stimulation; the average value of this in summer is 0.1 second. Hence the true period of transmission is 1.4 seconds for a distance of 15 mm. The velocity determined in this particular case is therefore 10.7 mm. per second. Precaution has to be taken against another source of disturbance, namely, the excitation caused by the sudden commencement or the cessation of the constant current. I have shown elsewhere[O] that the sudden initiation or cessation of the current induces an excitatory reaction in the plant-tissue similar to that in the animal tissue. This difficulty is removed by the introduction of a sliding potentiometer, which allows the applied electromotive force to be gradually increased from zero to the maximum or decreased from the maximum to zero. [O] BOSE--‘Plant Response’ (1906); ‘Irritability of Plants’ (1913). [Illustration: FIG. 45.--Complete apparatus for investigation of the variation of conducting power in _Mimosa_. A, storage cell; S, potentiometer slide, which, by alternate movement to right or left, continuously increases or decreases the applied E. M. F.; K, switch key for putting current “on” and “off” without variation of resistance; E, E′, electrodes of induction coil for stimulation; C, choking coil; G, micro-ammeter.]