394 LIFE MOVEMENTS IN PLANTS 



chamber was gradually raised from 29° to 33°C. at the point 

 marked with arrow. It will be seen that the positive curvature 

 became arrested, neutralised, and finally reversed into negative 

 (Fig. 146b). 



Fig. 146. — Effect of rise of temperature on phototropic curvature, (a) normal 

 positive curvature followed by recovery, (6) reversal of positive into negative 

 curvature by rise of temperature at (.H). (Pea seedling). 



After-effect of rise of temperature : Experiment 147. — The 

 after-ej[fect of rise of temperature exhibited by this specimen 

 was extremely curious. The temperature of the chamber was 

 allowed to return to the normal, and the experiment repeated 

 after an hour ; the response was now found to be negative 

 (Fig. 147a). It appeared probable that the temperature in the 

 interior of the tissue had not yet returned to the normal, and 

 an interval of four hours was therefore allowed for the res- 

 toration of the tissue to the normal temperature of the room. 

 The response still persisted to be negative, as seen in the series of 

 records obtained under successive stimulations of light of short 

 duration ; these negative responses exhibited recovery on the 



