218 Prof. Bose and Mr. Das. Physiological Investigations with 



tract E'P, the conducting power of which will be found appropriately 

 modified under the action of chemical and other agents. In this normal 

 method of mounting, the more excitable lower half of the pulvinus is below ; 

 excitatory reaction produces the fall of the petiole, gravity helping the 

 movement. The preparation may, however, be mounted in the inverted 

 position, with the more excitable lower half of the pulvinus facing upwards 

 as in (b). The excitatory movement will now be the erection of the petiole, 

 against gravity. 



Under natural conditions the stem is fixed, and it is the petiole which 

 moves under excitation. But a very interesting case presents itself when the 

 petiole is fixed and the stem free. Here is presented the unusual spectacle 

 of the plant or the stem " wagging " in response to excitation. In (c) the 

 more excitable lower half of the pulvinus is to the left, and under excitation 

 the stem at the left side undergoes a fall, while that on the right is erected. 

 It will be seen how, by having the two lengths of the stem equal, the action 

 of gravity is neutralised. 



2. The Change of Excitability after Immersion in Water. 

 The isolated specimen can be kept alive for several days immersed in water. 

 The excitability of the pulvinus, however, undergoes great depression, or even 

 abolition, by the sudden change of turgor brought on by excessive absorption 

 of water. The plant gradually accommodates itself to the changed condition, 

 and the excitability is restored in a staircase manner from zero to a 

 maximum. 



In studying the action of a chemical solution on excitability, the solution 

 may be applied through the cut end or directly on the pulvinus. The sudden 

 variation of turgor, due to the liquid, always induces a depression, irrespective 

 of the stimulating or the depressing action of the drug. The difficulty may 

 be eliminated by previous long-continued application of water on the pulvinus 

 and waiting till the attainment of uniform excitability which generally takes 

 place in the course of about three hours. Subsequent application of a 

 chemical solution gives rise to characteristic variation in the response. 



3. Quantitative Determination of the Rate of Decay of Excitability in an 



Isolated Preparation. 

 In order to test the history of the change of excitability resulting from 

 the immediate and after-effect of section, I took an intact plant and fixed the 

 upper half of the stem in a clamp. The response of a given leaf was now 

 taken to the stimulus of an induction shock of 0*1 unit intensity, the unit 

 chosen being that which causes a bare perception of shock in a human being. 



