224 



PLANT RESPONSE 



and its restoration may not take place for one or more 

 hours. 



An interesting experiment, on the abolition of conduc- 

 tivity under ether, was performed with a specimen of Bio- 

 phytum having eight leaves of fairly equal sensitiveness. Of 

 these, four, taken alternately, had ether applied on those 

 portions of their petioles which were next to the stem. On 

 now applying strong thermal stimulus on the stem, the state 



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L W> 



Fig. 98. Diagrammatic Representation of Experiment on Biophytum 



Ether was applied on the alternate petioles marked 1, 2, 3, 4. Stimulus 

 at x is prevented from acting on the leaflets of these leaves. 



The same diagram also represents the subsequent experiment on variation 

 of receptive excitability. Ether is applied at E instead of on the 

 petioles. Stimulus applied at E now produces no excitation. 



of excitation radiated to all the leaves. But the passage of 

 stimulus through the four etherised petioles was blocked, 

 and no effect was produced on their leaflets. The leaflets of 

 the non-etherised leaves, however, promptly responded, falling 

 one after another from the centre outwards (fig. 98). 



Variation of receptivity by anaesthetics. — Lastly, we 

 shall inquire into the variation of excitability at the point of 

 application of stimulus, that is to say, into the modification 

 of the plant's receptivity, under the action of an external 

 agent. It is to be borne in mind that stimulus coming from 



