416 Prof. Burdoii- Sanderson and Mr. F. J. M. Page [Dec. 14, 



summed with its predecessors and successors, to the bringing about of 

 the visible effect which follows e. Duriug the remainder of the process 

 the operation of the same law shows itself in the gradual augmentation of 

 the increments, the last contractiou, that by which the leaf closes, being 

 the result of the summation of the excitation which immediately pre- 

 ceded it with all the previous excitations. Our conception of the nature 

 of the process may be otherwise expressed by sayiug, that under the 

 influence of successive excitations the latent excitability of the leaf gra- 

 dually increases ; for whereas before it either made no response or post- 

 poned its response indefinitely, it now answers to the same stimulus by 

 a visible motion of which the promptitude and the extent increase 

 together. 



In one of our experiments we arranged our apparatus in such a manner 

 as to obtain a graphic record of the successive approaches of lobe to lobe 

 by which closure is ushered in ; a reduced, but otherwise accurate, copy of 

 this record is given in fig. 3, It shows a fact which we had already ascer- 



tained by observation, namely, that in each approach the rate of motion 

 augments rapidly at the beginning, and then very slowly subsides. It 

 was for this reason that we allowed two minutes to elapse between each 

 excitation and its successor ; for if the interval were less, the effect of the 

 excitation began before that of the previous one had ceased. In the 

 experiments represented graphically the excitations were repeated every 

 minute, so that the lever was still rising at the moment that each new 

 ascent commenced. 



It appeared important to ascertain whether, after the leaf is closed, it 

 still continues to make mechanical efforts. We had already observed 

 that a leaf which is repeatedly excited after closure seems to be clenched 

 with greater and greater force, and we thought it probable that mechanical 

 work would continue to be done by a leaf after closure if it had the 

 opportunity. To test this, all that was necessary was to attach weights 

 to our lever sufficient to keep the lobes expanded. The result of a single 



