568 LIFE MOVEMENTS^ IN PLANTS 



(a) is seen the normal diurnal curve ; the specimen was 

 inverted, and it took an entire day for the plant to 

 readjust itself to the new geotropic condition. The record 

 (&) was recommenced on the second day after inversion ; 

 the persistence of previous movement is seen in the 

 reversed curve during the first half of the second day ; 

 but in the second half the record became true, and the 

 third day the inverted plant gave a record which, from 

 an external point of view, was similar to that given by 

 the plant in the normal position. 



SUMMARY. 



A continuity is shown to exist between the thermo- 

 geotropic response of rigid trees, stems, and leaves of 

 plants. 



The diurnal record exhibits an erectile movement from 

 thermal-noon to thermal-dawn, and a movement of fall 

 from thermal-dawn to thermal-noon. 



In contrast with thermonastic movement which takes 

 place in growing organs, thermo-geotropic movement 

 takes place in fully grown organs including rigid trees. 

 The thermonastic movement is independent of the direction 

 of gravity, while in thermo-geotropic reaction, the stimulus 

 of gravity exerts a directive action. 



The effect of variation of temperature on the diurnal 

 movement is demonstrated by induced change of normal 

 rhythm, by artificial transposition of periods of thermal 

 inversion, and by the abolition of periodic movement 

 under constant temperature. 



The effect of stimulus of gravity on the diurnal move- 

 ment is demonstrated by the effect induced on holding 

 the plant upside down. The direction of the daily move- 

 ment is found to be determined by the directive action 

 of the stimulus of gravity. 



