62 Mr SpittaPs Repetition qf' Dutrochefs Experiments 



veyed was evident, from the effects manifesting themselves at 

 the lower part of the stem first, and proceeding progressively 

 upwards. I have tried other stimuli, such as caustic and a 

 heated iron-wire, which perhaps answers best. It is more con- 

 venient in experimenting, for it may be had at any time, which 

 cannot be said of the bright sunshine, more especially in this 

 country, and does not destroy the leaves like caustic, it not being 

 necessary to touch, nor even to apply it so near as to scorch them ; 

 it also appeared to me to act more certainly than any other sti- 

 mulus in causing the flexion of the leaves, and its impressions 

 seemed to be generally conveyed further than those of any 

 other. After the application of these stimuli, the leaves became 

 erect, but not for a considerable time, longer or shorter, accord- 

 ing to the state of the atmosphex-e, which appears to have great 

 influence on their action, this being always in most perfection 

 durino- warm moist weather, and bright sunshine. The leaves, 

 on becoming erect, I have always found as sensitive as before 

 the application of the stimuli mentioned, but Professor Graham 

 has found that this property is completely destroyed, for a much 

 longer period, by the application of the vapour of hydrocyanic 

 acid to the leaves of the plant, than after other stimuli. 



The part of the plant which conveys these impressions, M. 

 Dutrochet believes to be situated in the woody fibres alone. I 

 have not repeated all his experiments to prove this, having been 

 unable to procure plants sufficiently large for the purpose, but 

 I performed one, and that in the following way : I removed all 

 the cellular structure composing the external part of the bour- 

 relet, and left only the small bundle of woody fibres in the 

 centre, having previously supported the leaf so treated, with a 

 glass rod. On applying the heated iron-wire or lensto the leaf, af- 

 ter this operation, the impression was conveyed to the other 

 parts of the plant, and the usual consequences of such an applica- 

 tion took place, apparently little, if at all, impaired in intensity. 



M. Dutrochet, in another experiment, reversed that just de- 

 scribed ; that is, he removed the central bundle of vessels, and 

 left only the external cellular part of the bourrelet, after which 

 he found, on applying similar stimuli, that these impressions 

 were not all conveyed ; but this experiment I have not repeat- 

 ed : it is a very delicate one, and can only be done in large 

 plants. 



