68 



PLANT RESPONSE 



curvature, owing to the fact that opposite reactions neutralise 

 each other. 



I succeeded in obtaining a singularly perfect demonstration 

 of the response of a radial organ to local and unilateral stimula- 

 tion, by paying special attention to the selection of the specimen 

 and mode of stimulation. 1 took a pistil of Musa paradisiaca, in 

 which I was able to localise with great distinctness the zone of 

 growth, in this particular case of not greater extent than 2 mm. 

 The stimulation, which was thermal, was effected by placing 

 on one side of the selected area, but not in actual contact with 



it, the outer point of 

 a small V-shaped 

 piece of platinum 

 wire which could be 

 put in circuit with a 

 battery. An exactly 

 similar arrangement 

 was made on the 

 other side of the 

 organ, at the dia- 

 metrically opposite 

 point. By sending a 

 heating current from 

 the battery through 

 either of the plati- 

 num pieces for a de- 

 finite length of time, 

 the tissue in that region is stimulated locally by thermal 

 radiation. In this manner two opposite points of the tissue 

 may be alternately subjected to equal stimulation. The 

 accompanying figure (fig. 34) g ives the record of such 

 an experiment. The up-responses here represent the con- 

 cavity produced by stimulating on one side, say the right, 

 and the down-responses the same on the left. It will thus 

 be seen that equal and opposite responses were obtained, 

 equal alternate stimulation of the two sides. The recovery, 

 it will be noticed, is not complete, the curvature caused by 



Fig. 34. Alternate opposite-directioned Re- 

 sponses obtained by the successive Unilateral 

 Stimulations of opposite sides of Pistil of 



Musa 



r, responses of right side, upwards ; L, re- 

 sponses of left side, downwards. 



