CIKCUMNUTATION 377 



arise from the fact that the optimum point of some variation, 

 such as a change of turgor or a change of temperature, 

 may be reached earher in the more active half than in 

 the less active. 



• 



Preliminary Adjustments 



In working with cut specimens it is found that the 

 .torsion is at first clockwise (negative), instead of being 

 anti-clockwise (positive). I was able to trace this reversal 

 to the effect of the strong stimulation caused by section. 

 If, after mounting, the cut specimen be left undisturbed, the 

 normal torsion will be found to be fully restored after a 

 period of rest of about an hour. In obstinate cases, recovery 

 is hastened by immersion of the cut stem in tepid water. 

 It should be borne in mind that any rough handling acts 

 as a stimulus, and may thus retard or even reverse the 

 direction of the normal torsion. 



Autonomous Torsional Circumnutation 



Experimental investigations have been carried out with 

 a number of species of twining plants, such as Thun- 

 bergia gigantea, Thunhergia coccinea, P or ana paniculata, 

 Ipomoea, Clitoria Ternatea, and the common Phaseolus. 

 The researches were carried out under widely varied climatic 

 conditions. Tropical conditions prevailed in my Institute 

 in Calcutta, the mean temperature for 24 hours being about 

 30° C. in summer. Colder conditions existed at my Research 

 Station at Mayapuri, Darjeeling, situated at a height of 

 7000 feet, the mean temperature in summer being 18° C. 



Experiment 201. Rate of circumnutation. — I will first 

 describe the movement of the horizontally inclined apex of 

 Thunhergia coccinea growing wild on the hill-side at Darjeeling. 

 This movement of circumnutation is to be distinguished 

 from the torsional movement of the erect stem. The method 

 of observation of circumnutation will be understood from 



