AUTONOMOUS TORSION 67 I 



light, if the specimen were in a sub-tonic condition, would 

 be, by increasing the internal energy, to give rise to an 

 enhanced rate of growth ; but when the normal tonic 

 condition had been attained by absorption of light, the 

 subsequent responses would be by a movement opposite to 

 that of growth-elongation — that is to say, a contraction or 

 retardation of growth. In experimenting on the effect ot 

 light on the autonomous torsional movements of the stems 

 of certain specimens of IpoiiiKa, I have met with results 

 exactly parallel — ^that is to say, the natural rate of torsional 

 movement, in this case negative, was transitorily enhanced 

 by the first incidence of light, but declined and underwent 

 reversal after continued action of stimulus. In the second 

 and subsequent responses this preliminary enhancement was 

 found to have disappeared, the effect of light now being a 

 retardation and subsequent reversal of the natural torsional 

 movement. 



Effect of electric current.— I have often observed a 

 very interesting effect, as induced by a constant current 

 flowing along the length of the organ. During the continu- 

 ance of the current the normal torsional response is first 

 decreased and then reversed. On the cessation of current 

 there is recovery and restoration of the normal direction of 

 torsion. If the current maintained be strong or long con- 

 tinued, the induced reversal may become more or less 

 persistent. Such an induced reversal of torsion, moreover, 

 is independent of the direction of current. 



Effect of gravity. — I shall next describe a series of 

 effects which I have only been able to obtain with any 

 degree of certainty under favourable conditions. Where 

 natural torsion is feeble the retarding effect of gravity which 

 I am about to describe is such as to arrest torsion, and it is 

 difficult to decide whether such arrest is accidental or in- 

 duced. When the specimen, on the other hand, is too 

 vigorous, the retardation is not easily observed, probably 

 because it tends to be masked by the natural movement. In 

 practice, therefore, the best specimens are those characterised 



