Petiole- Pulvinus Preparations of Mimosa pudica. 217 



enclosed in a small chamber and subjected to varying conditions of tempera- 

 ture and to the action of different vapours and gases. Drugs are easily 

 absorbed at the cut end, and a poison and its antidote can be successively 

 applied through the funnel without any disturbance of the continuity of 

 record. In fact, many experiments which would be impossible with the 

 entire plant are quite practicable with the isolated leaf. 



The arrangement for taking records of response is seen in fig. 1, which is 

 reproduced from a photograph of the actual apparatus. For recording the 

 response and recovery of the leaf under stimulation, I use my Eesonant 

 Recorder fully described in the ' Philosophical Transactions.'* The petiole is 

 attached to one arm of the horizontal lever. The writer, made of fine steel 

 wire with a bent tip, is at right angles to the lever, and is maintained by 

 electromagnetic means in a state of to-and-fro vibration, say, ten times in a 

 second. The record, consisting of a series of dots, is free from errors arising 

 from friction of continuous contact of the writer with the recording surface. 

 The successive dots in the record at definite intervals of a tenth of a second 

 also give the time-relations of the response-curve. 



On account of its small size, the petiole-pulvinus preparation offers great 

 facilities for mounting in different ways suitable for special investigations 

 (fig. 2). Ordinarily the cut stem with its lower end enclosed in moist cloth 



(a) (b) (c) 



Fig. 2. — Petiole-pulvinus preparation : (a) normal position ; (b) inverted position ; 



(c) " wagging " of stem. 



is supported below as in (a). A very suitable form of stimulus is that of 

 induction shock from a secondary coil, the intensity of which is capable of 

 variation in the usual manner by adjusting the distance between the primary 

 and the secondary coils. The motile pulvinus, P, may be excited directly 

 b y applying the exciting electrodes at E and E". For investigations on. 

 velocity of transmission of excitation, stimulus is applied indirectly by means 

 of the electrodes at E and E'. Excitation is now transmitted along the 



* Ibid, 



VOL. LXXXIX. — B. T 



