226 CHAP. XXI. THE ' PRAYING ' PALM 



persist after the death of the tree ; if physiological, the 

 movement would disappear. 



The tree was old and died a natural death a year after 

 the commencement of my investigations. I then received 

 a communication from the Government officer in charge of 

 the district, that ' the palm tree is dead and its movements 

 have ceased.' This afforded conclusive evidence that the 

 movements had in some way been due to its vital activity. 



The periodic movement of the tree must therefore be 

 attributable to the physiological response of the living cells 

 to the diurnal changes of the environment — either the 

 recurrent alternation of light and darkness, or the diurnal 

 changes of temperature. The only certain way of dis- 

 criminating the effect of the one from that of the other was 

 to obtain a continuous record of the movement of the tree, 

 and find whether light or temperature maxima coincide 

 with the maximal displacement of the tree. 



The objects of the investigation resolved themselves 

 into the following : 



1. A method of accurate and continuous record of the 



tree day and night for the determination of the 

 exact times of maximum erection and of fall ; 



2. Comparative determination of the effects of diurnal 



variations of light and of temperature ; 



3. To ascertain whether the characteristic movement of 



the particular Palm was unique, or whether it was 

 of more or less universal occurrence ; and 



4. Determination of the relatively more effective factors 



in the production of the diurnal movement. 



The problem is complicated, the movement of the tree 

 being modified by so many factors. This was realised 

 during the course of my investigations on the subject, now 

 extending over twelve years. I will first describe the effects 

 observed under diverse experimental conditions, which have 

 led to the disentanglement of the individual effects of the 

 several factors in operation. 



