RESPONSE OF DIGESTIVE ORGANS 



343 



curious and interesting to note here, as in the case of 

 Nepenthe, the trend of the base-line up, when the response 

 is the normal negative, and down when it is the reversed 

 positive, indicating in the one case increasing negativity, and 

 in the other increasing positivity. 



As in the Nepenthe, so also in the leaf of Drosera, 

 specimens which are not fresh that is to say, previously 

 unexcited are apt to exhibit the positive phase of response. 

 I give below a series of multiple 

 responses (fig. 209) induced in such 

 a leaf by a strong stimulation. The 

 stimulus was in this case given by 

 sectioning the leaf, and the response 

 therefore illustrates the fact that 

 preparation itself acts as a stimulus. 

 In the present case, electrical con- 

 nections with the galvanometer, 

 were made with the upper and 

 lower surfaces of the leaf on the 

 plant, intact. On now cutting the 

 petiole across, a long series of 

 multiple responses, lasting for about 

 45 minutes, was found to be set 

 up. These pulsations were at first 

 rapid, and then slowed down 

 gradually, the average period of a 

 single pulsation being about 30 

 seconds. Only a portion of the 

 record is shown in fig. 209. 



Having thus seen the typical responses exhibited by 

 the digestive organs of plants, we shall now pass to the 

 consideration of the reactions induced in animal stomachs. 

 Here, again, two different subjects of inquiry arise, the 

 direction, namely, of the natural current of rest, and that of 

 the action or responsive current. As regards the first of 

 these, it will be remembered that Rosenthal found it to be 

 strongly ' ingoing ' that is to say, from the mucous to the 



FIG. 209. Photographic Record 

 of Multiple Response of Leaf 

 of Drosera in Positive Phase 



Stimulus was caused here by 

 section of the petiole. 



