240 CHAP. XXII. DIURNAL MOVEMENTS OF PLANTS 



Experiment 131. — The diurnal records of adult leaves 

 of a number of plants, such as DahUa, Papaya, Croton and 

 others, exhibit the same characteristics as shown by the 

 Palms and by the geotropically curved stems. In all these, 

 the fall of temperature from thermal noon to thermal dawn 



Fig. 139. Abolition of diurnal movement in Tropaeolum under 

 constant temperature, and its restoration under normal daily 

 variation. The upper record is of temperature and the lower 

 of plant-movement. The horizontal parts of the record 

 relate to the period of constant temperature. 



induced an up-movement of the leaf, while rise of temperature 

 from thermal dawn to thermal noon caused a fall (fig. 140). 

 There is an individuality which characterises the record of 

 each species of plant, and thus makes it possible to identify 

 it from its autograph. 



The facts given above appear to indicate that organs 

 previously subjected to gravitational stimulation exhibit 

 characteristic diurnal movements under variation of tem- 



