566 LIFE MOVEMENTS IN PLANTS 



diurnal variation of temperature. The record of the plant 

 is seen to exhibit once more its normal periodic movement. 

 I have in the chapter on thermo-geotropism (p. .515) shown 

 that the diurnal movement of a geotropically curved 

 organ is determined in reference to the direction of force 

 of gravity. This will be seen demonstrated in an inter- 

 esting manner in the two following experiments on the 

 effect of invevsion of the plant on daily movement. 



DIURNAL MOVEMENT IX INVERTED POSITION. 

 I have already referred to the distinction that is made 

 between nastic and paratonic movements. In the former 

 the movement is autonomous and in relation to the plant, 

 and in the latter it is due to an external force which 

 determines the direction of movement. In nastic reaction, 

 closure movement would persist as a closure movement* ; 

 but should the direction of movement be determined by 

 the stimulus of gravity, closure movement would, on inver- 

 sion, be reversed into an opening movement. Viewed from 

 an external point of view an up-movement in the latter 

 case would, after readjustment on inversion, become an up- 

 movement, though in so doing, the expansion should be 

 transferred from the upper to the lower side of the organ- 

 It is to be understood in this connection, that some time 

 must lapse before this readjustment is possible, and that 

 the former movement may continue, in certain cases, as 

 a persistence of after-effect. 



I succeeded in demonstrating the paratonic effect of 

 geotropic stimulus on the periodic movement of the palm 

 leaf, by holding the plant in an inverted position (p. 24)- 

 On the iirst day of inversion, the diurnal record was 

 erratic, but in the course of 24 hours, the leaf readjusted 

 itself to its unaccustomed position, and became somewhat 

 erected under geotropic action. After the attainment of 



* By closure is meai.t movement of opposite pairs of le»f-organ8 towardg 

 each other. 



