210 



CIRCUMNUTATION. 



[CH. VIII 



of the plant serves as a medium on which to record the 

 movement. The head of the observer is moved until the 

 globule of sealing-wax is exactly in the centre of the 

 paper triangle, and a dot is made on the glass in line 



Fig. 42. Exp. 258. 



with these two points. The dot should be made with a 

 piece of hard wood cut to a sharp point like a pencil, and 

 dipped in Indian ink or moistened with water-colour. It 

 is best to hold the pointer as close as possible to the 



