DtfffUta Miiscipula, i'.llis. 13 



lime in secnn<U 

 whl( )i el ■ 

 between con- 

 .ind tin- 

 Number of Angular measure- lirst perceptible 

 excitations. ment of effect. approach. 



I to 7 O OO 



8 o 00 



9 o 00 



10 Y\ 1 5-5 



11 U 10.8 



•2 # 7-3 



13 1 5-8 



'4 I# 5-o 



15 & 1-5 



16 2}i 5.2 



'7 3 2-5 



l8 2 7.6 



•9 1% 3-8 



20 3H 37 



2i AK 3-3 



22 S l /z 4-o 



23 7 2.7 



24 «K 2.5 



25 8 not observed. 



26 10 2.2 



27 '. . . at 27th excitation the leaf closed. 



" From this experiment, which was repeated several times 

 and always gave similar results, it was learned : (1) that the 

 first half-dozen excitations were absolutely without mechanical 

 effect ; (2) that the first effectual excitation was followed by 

 so slight a movement that if it had not been enlarged by the 

 lever it would have been imperceptible, and (3) that after this 

 each successive approach of the lobes in most cases exceeded 

 its predecessor." 



" The time measurements, as will be seen at a glance, stand 

 in a remarkable relation to the mechanical effects, showing 

 that the delay between excitations and effects diminishes as 

 the extent of the effect increases, like facts having the same 

 meaning, viz., that in the plant, as in certain cases well known 

 to the animal physiologist, inadequate excitations when re- 

 peated exercise their influence by what has been termed 

 summation, i. c, that when any number of such stimulations, 

 say a, b, c, d, c, etc., follow each other in succession, the effect 



