366 ' LIFE MOVEMENTS IN PLANTS 



petiole of Mimosa when locally stimulated does not itself 

 exhibit any movement. The fortunate circumstance of the 

 presence of a motile pulvinus in the neighbourhood enables 

 us to recognise the perceptive power of the petiole, since 

 it transmits an impulse which causes the fall of the leaf. 

 There is no motile pulvinus in ordinary leaves, and 

 stimulation of the petiole gives rise to no direct or trans- 

 mitted motile reaction ; from this we are apt to draw the 

 inference that the petiole of ordinary leaves are devoid of 

 perception. This conclusion is, however, erroneous, since 

 under stimulus the petiole exhibits the electric response 

 characteristic of excitation. Moreover my electric investi- 

 gations have shown that every living tissue not only 

 perceives but also responds to stimulation.* Hence con- 

 siderable doubt may be entertained as regards the 

 supposed absence of perception in the hypocotyl of Setaria. 



T shall in the present paper describe my investigations 

 on the mechanical response of Setaria under direct and 

 indirect stimulation which will be given in the following 

 order : — 



(1) The response to unilateral stimulation of the tip 



of the seedling. 



(2) The response of growing hypocotyl to direct sti- 



mulation. 



(3) Summated effects of direct and indirect stimula- 



tion. 



EXPERIMENTAL ARRANGEMENTS. 



The Recorder. — The pull exerted by the tropic curva- 

 ture of the seedling is very feeble ; it was therefore 

 necessary to construct a very light and nearly balanced 



* " Response in the Living and Non-Living " — p. 17. 



