CHAPTER IX 



PLANT RESPONSE 



AT the outset of this intricate subject a brief and per- 

 sonal outline may be given. In his investigations on 

 response in general Bose had found that even ordinary 

 plants and their different organs were sensitive exhibiting, 

 under mechanical or other stimuli, an electric response, 

 indicative of excitation. If this were so, it puzzled him 

 greatly that so-called ordinary plants should not give 

 any indication of excitation by visible movement. In the 

 best known of sensitive plants, Mimosa, the leaves, on being 

 irritated, strikingly respond by a sudden fall of the leaf, 

 due to contraction of the lower half of the cushion-shaped 

 and joint-like leaf -base, the ' pulvinus/ Bose noted that 

 the contraction of the pulvinus was small ; it was the long 

 leaf-stalk which here acted as a magnifying index. He 

 therefore thought that the .contraction due to excitation 

 may be present in ordinary plants, and may only have 

 escaped the attention of other workers. To test this antici- 

 pation, he attached a similar magnifying device to ordinary 

 plants, and was rewarded by finding that they too 

 answered to stimulus by a distinct contraction. He there- 

 fore entered into a long series of investigations in which 

 the mechanical response of the plant indicated its state of 

 excitation. 



For recording the responsive movement Bose employed 

 his device of the ' Optical Lever/ by which the movement 

 was greatly magnified. He was thus able to demonstrate 



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