280 LIFE MOVEMENTS IN PLANTS 



had hitherto remained a matter of uncertainty. In regard 

 to this we must bear in mind that it is the effect of 

 indirect stimulus that reaches the distal sided, inducing an 

 enhancement of turgor and expansion of that side. 



For obtaining a complete explanation of tropic curva- 

 tures in general, it is important that the induction of en- 

 hanced turgor at the distal side (by the action of stimulus 

 at the proximal side) should be corroborated by independ- 

 ent methods of enquiry. One of the methods I employed 

 for this purpose was electrical. Two electric connections 

 were made, one with the distal point (diametrically oppo- 

 site to the stimulated area), and the other, with an indiffer- 

 ent point at a distance. On application of stimulus of 

 various kinds, the distal point was found to exhibit gal- 

 vanometric positivity, indicative of enhancement of turgor.* 



I have since been able to devise a new experiment by 

 which the enhancement of turgor on the distal side is 

 demonstrated in a very striking manner. 



I have shown (p. 39) that the movement of the 

 motile leaf of Mimosa is a reliable indicator of the state of 

 turgor, increase of turgor inducing erection, and diminution 

 of turgor bringing about the fall of the leaf. I shall 

 employ the mechanical response of the leaf to demonstrate 

 the enhancement of turgor induced by transverse trans- 

 mission of effect of stimulus. 



TURGOR-VARIATION UNDER TRANSVERSE TRANSMISSION 

 OF STIMULUS-EFFECT. 



Unilateral photic stimulation : Experiment 104. — A Mimosa 

 plant was taken, and its stem was held vertical by means 

 of a clamp. We apply a stimulus at a point on one side 

 of the stem, and observe the effect of this on the state 

 of turgor at the diametrically opposite side. In my first 



* " Plant ResponbC " — p. 519. 



