238 CHAP. XXII. DIURNAL MOVEMENTS OF PLANTS 



2.45 P.M. to thermal dawn next morning at 6 a.m., that is 

 to say, for nearly 16 hours. Rise of temperature occurred 

 through the same range in about 8 hours. The average 



Fig. 138. Diurnal curve of the procumbent stem of Tropaeolum 

 majus and of the leaf of Dahlia for two successive days. 

 In the thermographic record the up-curve represents fall, 

 and down-curve rise of temperature. 



rate of rise of temperature was thus about twice as quick 

 as the average fall, very clearly shown by the difference in 

 the slopes of the curve during thermal descent and ascent.. 



