DAILY MOVEMENT DUE TO THERMO-GEOTROJPlSM 559 



the stable position of geotropic equilibrium. In figure 200 

 is given records of the inclined palm tree, of procumbent 

 stem of Tropu'u/um, and the leaf of the palm tree. The 

 very close relation between the temperature-variation and the 

 movement of different plant-organs is sufficiently obvious. 



I shall next give a series of diurnal records of leaves 

 of different plants such as those of Dahlia, Papaya and 

 Croton (Fig. 201). In these also fall of temperature induces 

 an up-movement while rise of temperature causes a fall 

 of the leaf. I shall presently refer to the ' personal 

 equation ' by which the record of one plant is distinguished 

 from another. 



CONTINUOUS DIURNAL RECORD FOR SUCCESSIVI-: THP^RMAL 



NOONS. 



Experiment 211. — The diurual record given above, was 

 taken from ordinary noon at 12 o'clock to noon next 

 day. The diurnal curve becomes much simplified if the 

 record be taken from tJiermal-noon (at about 2 p.m.) to 

 the thermal noon next day. The plant-organ becomes 

 erected during falling temperature from thermal-noon to 

 thermal-dawn next morning, and undergoes a fall during 

 rise of temperature from thermal-dawn to thermal-noon. 

 The subsequent diurnal records will therefore be given for 

 24 hours commencing with 2 p.m. In figure 202 is given 

 diurnal records of geotropically curved stem of Tropce- 

 olum and the leaf of Dahlia for two days in succession. 



The thermal record shows that there was a continuous 

 fall of temperature from thermal-noon at 2 p.m. to the 

 thermal-dawn at 6 a.m. next morning, that is to say, for 

 IG hours. Rise of temperature through the same range 

 occurred in 8 hours from C a.m. till 2 p.m. The averages 

 rate of rise of temperature was thus twice as quick a- 

 that of fall. This is clearly seen from the slopes of therr 

 mal curve during thermal ascent and descent. The recod 



