the Leaves of the Sensitive Plant, 83 



intumescence was divided by a longitudinal incision, made ver- 

 tically instead of horizontally. 



I have already mentioned that Dutrochet discovered that the 

 ligneous fibre is the channel, along which an impression is 

 conveyed from one part to another. Mr. Burnett and myself 

 had made one or two experiments upon the course which the 

 irritation follows when spreading from leaflet to leaflet, where 

 several are placed upon the same petiole. 



If the upper third of a petiole bearing four leaflets be di- 

 vided longitudinally, the irritability of the leaflets remains for 

 many days unimpaired ; upon cutting with scissors one snb- 

 leaflet after the plant has recovered itself, the irritation is ob- 

 served to descend the wounded leaflet, and then to pass to that 

 adjoining upon the same side of the petiole : afterwards the 

 petiole falls, but there the effect stops ; it does not extend to 

 the two other leaflets ; the direct route is cut through, and the 

 irritation seems to find no circuitous way, as might have been 

 expected, perhaps through the intumescence of the petiole back 

 again to the leaflets, on its summit. If on a petiole, bearing 

 four leaflets, a lateral incision be made, cutting the petiole half 

 through it at a point between the two leaflets which are situated 

 on one side, upon irritating either of the leaflets, between which 

 the incision has been made, it folds its subleaflets ; then the 

 two opposite leaflets fold their subleaflets ; and last of all, the 

 leaflet next adjoining that first irritated, but isolated from, it 

 by the incision, becomes folded. 



In the few remarks which I have thus put together, I have 

 quoted Lindsay and Dutrochet only as far as their researches 

 anticipated my own : I leave unnoticed many experiments, in 

 several of which these authors are again found to have acci- 

 dentally coincided. The experiments to which I allude do 

 not, however, serve to illustrate the nature of the motion ex- 

 hibited by the sensitive plant, to the examination of which sub- 

 ject alone my attention was, in the present instance, directed, 

 in the expectation that it might throw light upon the obscure 

 and interesting subject of muscular action. 



I remain, my dear Sir, Your's truly, 



Herbert Mayo. 

 19, George Sireety Hanover Square, 

 August 29, 1827. 



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