62 PLANT RESPONSE 



with a comparative sluggishness which, generally speaking, 

 is not so great as that of PhilantJius. In the following 

 experiments various leaves were excited by strong electric 

 shocks, sent through the entire length of the petiole, and 

 responsive movements were, as a rule, observed, the leaves in 

 these instances falling downwards from their normal more or 

 less horizontal position. Of these I shall give only three 

 instances. A particular leaf of Bryophyllum calcynum, which 

 is unprovided with a pulvinoid, was 5 cm. in length. After 

 tetanic shocks of three minutes, the leaf fell, the distance 

 traversed by the tip being T\ cm. A leaf of Canna indica, 

 again, unprovided with any pulvinoid and not too young, 

 was 20 cm. in length. On the application of tetanic shocks 

 for one minute, the leaf fell, the distance traversed by the 

 tip being as much as 14 cm. The third instance is a leaf 

 oi Fiats religiosa^ 14 cm. in length. After three minutes of 

 continuous stimulation, the leaf fell, the tip passing through a 

 distance of 12 cm. It will thus be seen that the movement 

 caused by stimulation in ordinary leaves is quite considerable. 



It may, however, be objected that the fall of the leaf is 

 really due simply to its weight, acting on the petiole when 

 rendered flaccid. Even in this case the flaccidity would be 

 directly due to stimulation, and the movement of the Mimosa 

 leaf itself must be regarded as being of a similar nature. 

 But in order to prove that the movement of the leaf is 

 mainly due to the active differential contraction of the upper 

 and lower halves, and in order to eliminate completely the 

 effect of weight, I arranged the experiments as follows : 

 The plant was held with the leaf directed vertically down- 

 wards. The movement due to the greater contraction of the 

 lower half of the organ, in consequence of the true excitatory 

 effect, ought now to raise the leaf against the force of gravity. 

 And this, as will be seen from the records (fig. 33), was found 

 to be the case. 



In order to compare the angular movements of some 

 ordinary leaves, and their time-relations, with those of 

 Mimosa, when subjected to strong electric shocks, I took 



