552 LIFE MOVEMENTS IN PLANTS 



Nyrnphcea is acted on in the evening by two antagonis- 

 tic forces ; darkness induces a movement of closure, and 

 fall of temperature gives rise to a movement of opening. 

 Since the flower opens in the evening, the predominant 

 effect is that of falling temperature. 



The above conclusions are fully borne out by the 

 diurnal record which I obtained with Nymphcea. 



Experiment 209. — One of the perianth leaves was attached 

 to one of the recording levers, the differential ther- 

 mometer being attached to the other. It will be seen 

 (Fig. 108) that the movement of the flower follows very 



Fig. 198.— Diurnal record of Nt/mphma. Upper record gives variation of 

 temperature; the up-curve representing fall, and down-curve rise of temperature. 

 The lower record exhibits the movement of the flower, up-curve representing 

 the opening, and down-curve the closure of the flower. 



closely the curve of variation of temperature. The flower 

 was tightly closed in the day time ; and the perianth leaves 

 began to open out in the evening at first slowly, then very 

 rapidly, and the flower becoming fully expanded by 10 p.m. 



