66o 



PLANT RESPONSE 



given in fig. 267. The downward arrow (i) indicates the 

 application of the chemical solution to the opposite flank. It 

 will be noticed that we have in consequence, in the dotted 

 portion of the record, a reversal of the first torsional response. 

 Torsional response of compound strip of ebonite and 

 stretched india-rubber. — Enough has already been said to 

 demonstrate the fact that the torsion induced in leaves by the 

 lateral application of light is not due to any specific sensibility 

 to light as such. I shall next therefore proceed to show that 

 the same torsion is the mechanical result of the differential 



Fk;. 268. Torsional Response of Leaf 

 of Mimosa to Lateral Chemical 

 Stimulus 



Upward arrow (f) indicates moment 

 of application of stimulus to one 

 flank ; ( J, ) indicates application of 

 stimulus to opposite flank, with effect 

 of reversing torsional movement. 



Fig. 269. Torsional Re- 

 sponse of Complex Strip 

 of Ebonite and India- 

 rubber under Lateral 

 Action of Strong Radia- 

 tion 



contraction of a complex organ, which is fixed at one end, 

 and subjected to lateral stimulation. I have in a former 

 chapter described an artificial model of the pulvinus of 

 Mimosa, which consisted of a compound strip, the upper half 

 of which was ebonite, and the lower the more contractile 

 stretched india-rubber. If such a strip be held securely at 

 one end in a clamp, and if the lateral flank, consisting half 

 of ebonite and half of india-rubber, be subjected to the 

 strong action of light, records being taken in the usual 

 manner, it will be found that a torsional response takes place 

 which is in every respect similar to that of the pulvinus of a 



