

CHAPTER XVIII 



RESPONSE OF LEAVES 



Observations of Burdon Sanderson on leaf-response in Dioncca Leaf-and- 

 stalk currents Their opposite variations under stimulus Similar leaf-and- 

 stalk currents shown to exist in ordinary leaf of Ficus religiosa Opposite- 

 directioned currents in Citrus decumana True explanation of these resting- 

 currents and their variations Electrical effect of section of petiole on Dionsea 

 and Ficus religiosa Fundamental experiment of Burdon Sanderson on 

 lamina of Dioiiaa Subsequent results Experimental arrangement with 

 symmetrical contacts Parallel experiments on sheathing leaf of Musa 

 Explanation of various results. 



IT was pointed out in Chapter II. that progress in the in- 

 vestigation of the subject of excitatory phenomena in plants 

 had been long delayed, in consequence of the prevalent idea 

 that only motile plant-organs were ' excitable.' The atten- 

 tion of investigators was thus mainly confined within the 

 narrow range of the so-called ' sensitive ' plants, such as 

 Dioncsa. It was also shown, in the same place, that the 

 results already arrived at by observers in this field had not 

 been altogether concordant, and presented many anomalies. 



As it has now been demonstrated, however, in the course 

 of previous chapters, that ordinary plants are fully sensitive, it 

 will be well to proceed to show that the various effects 

 observed in the 'sensitive' Dioncea may be still better studied 

 in ordinary leaves. It will be possible, moreover, by follow- 

 ing this line of inquiry, to determine those general laws, of 

 which the peculiarities observed in Dioncea are only instances ; 

 and thus we shall be the better able to offer an explanation 

 of such cases as now appear anomalous. 



Before doing this, I shall briefly recapitulate the principal 

 effects observed by Burdon Sanderson in the leaf of Dion<za. 



