484 



LIFE MOVEMENTS IN PLANTS 



Darwin in his Movements' of Plants described experi- 

 ments on the responsive behaviour of the tip of the radicle. 

 He produced unilateral stimulation in three differc^nt ways, 

 first by attaching minute fragments of cardboard to one 

 side of the root-tip ; this moderate and constant irritation 

 was found to induce a convexity on the same side of the 

 growing region, with the resulting negative movement, i.e., 

 away from stimulus. His second method was chemical, one 

 side of the tip being touched with silver nitrate ; the third 

 method of stimulation was a slanting cut. All these methods 

 induced a movement away from stimulus. 



ELECTRICAL RESPONSE TO INDIRECT STIMULATION. 



The next investigation was for the determination of the 

 electrical change induced in the growing region by applica- 

 tion of unilateral stimulus at the root-tip. 



Experiment 181. — One of the two electrical connections 



with the galvanometer is made 

 at one side of the growing region 

 A, the other connection being 

 made with the diametrically 

 opposite point B. Unilateral 

 stimulus was applied at the root 

 tip a, of the bean plant and on 

 the same side as A. I subjected 



Fig. 17L-Diagrammatic repre- ^^^ jj^ ^^ various modeS of uni- 



sentation of mechanical and electric 



response of root to indirect stimulus lateral Stimulation. Mechanical 

 applied at the tip a. Figure to stimulation was effected by emery- 



the left shows responsive move- p • ,. ^ • . , 



f ' . , ,p, paper friction or by pin-prick ; 



ment awa}' from stimulus. The r f j i f • 



electric response to indirect stimulus chemical Stimulation waS pro- 

 is indicated in the figure to the , ,, i-x- c til 



. ^, ^, . , ., ., duced by application or dilute 



right ; the point on the same side •' ^^ 



exhibiting gaivanometric positivity. hydrochloric acid. Thermal sti- 



The shaded part indicates the j^ulation was Caiised by the 

 responsive region of growth iit 



some distance from the tip. proximity of electrically heated 



platinum wire. In every case the response was by 

 induced galvanometnc positivity at A (Fig. 171). This 



