234 CHAP. XXI. THE * PRAYING ' PALM 



the string itself making a loop round the wheel, the lower 

 end of the string being tied to the spiral spring T. When 

 the tree is erecting itself, the wheel is rotated anti-clockwise, 

 the angle of rotation being read by the index on a circular 

 scale C. Fall of the tree causes clockwise rotation of the 

 wheel (fig. 136). By making the diameter of the wheel 

 sufficiently small the Diurnal Indicator can be made 

 extremely sensitive. 



From the results that have been obtained it would 

 appear that two conditions are necessary to ensure the 

 striking display of the periodic up and down movement of 

 the tree. The first is that the tree should have been rendered 

 anisotropic by the previous action of the stimulus of gravity ; 

 the second is that the tree should be subjected to the diurnal 

 variation of temperature. These, as well as other condi- 

 tions affecting the diurnal movement of plants, will be 

 treated in detail in the next chapter. 



Summary 



The ' Praying ' Palm of Faridpore, growing at an inclina- 

 tion of 60° to the vertical, exhibited a diurnal movement such 

 that its head became erected in the morning and lowered 

 towards the evening, the outspread leaves becoming pressed 

 against the ground. 



Diurnal records of temperature and of movement of the 

 tree show that the two curves closely resemble each other. 

 The rise of temperature was followed by the fall of the tree 

 and vice versa. 



The movement was not physical but physiological, as 

 was proved by cessation of all movement after the death of 

 the tree. 



The influence of light is negligible in the diurnal move- 

 ment. 



The movement is found to be essentially due to the 

 diurnal variation of temperature, a shght fluctuation of 



