The magnification of movement is produced by a light lever, the short arm of which is attached to the plant organ, the long arm tracing the record on a moving smoked plate of glass. The axis of the lever is supported by jewel bearings. The principal difficulty in obtaining accurate record of response of plant lies in the friction of contact of the recording point against the glass surface. This difficulty I have been able to overcome by providing a device of intermittent instead of continuous contact. For this, either the writer is made to vibrate to and fro, or the recording plate is made to oscillate backwards and forwards. 1. _The Resonant Recorder._--In this the writing lever is made of a fine steel wire. One end of this wire is supported at the centre of a circular electromagnet; this latter is periodically magnetised by a coercing vibrator, which completes an electric circuit ten hundred, or two hundred times in a second. The writing lever is exactly tuned to the vibrating interrupter and is thus thrown into sympathetic vibration. Successive dots in the record thus measure time from 0.1 to 0.05 second. The employment of the Resonant Recorder enables us to measure extremely short periods of time for the determination of the latent period or the velocity of transmission of excitation.[D] [D] For detailed description _cf._ Bose.--“An Automatic Method for Investigation of Velocity of Transmission of Excitation in _Mimosa_.”--Phil. Trans., B. vol. 204, (1913). 2. _The Magnetic Tapper._--Measurement of very short intervals is not necessary in ordinary records of response. In this type of recorders, the circular magnet is therefore excited at longer intervals, from several seconds to several minutes; this is done by completion of the electric circuit at the required intervals, by means of a key operated by a clock. 3. _The Mechanical Tapper._--In this, magnetic tapping is discarded in favour of mechanical tapping. The hinged writing lever is periodically pressed against the recording plate by a long arm, actuated by clock-work. 4. _The Oscillating Recorder._--Here the plate itself is made to oscillate to-and-fro by eccentric worked by a clock. The frame carrying the plate moves on ball-bearings. The advantage of the Oscillating Recorder lies in the fact that a long lever, made of fine glass fibre, or of aluminium wire, may be employed for giving high magnification. A magnification of a hundred times may be easily obtained by making the short arm 2.5 mm. and the long arm 25 cm. in length.[E] [E] Bose--“Researches on Irritability of Plants,” p. 279--Longmans, Green & Co. RESPONSE OF A RADIAL ORGAN. [Illustration: Fig. 10. Response of a straight tendril of _Passiflora_ to electric shock. Successive dots at intervals of 5 seconds. The vertical lines below are at intervals of a minute. In this and in all following records (unless stated to the contrary) up-curve represents contraction, and down-curve expansion or recovery.]