248 RESEARCHES ON IRRITABILITY OF PLANTS 



stimulus of descending make current applied as before at c. 

 It will be seen that not only is the stimulus now effective, 

 but the amplitude of response is much greater than that of 

 normal response at 30 C. In order to test these results 

 further, the experiment was repeated under alternate heat- 

 ing and cooling. It will be noticed that under rising tem- 

 perature there is an invariable failure of excitation, while 

 under lowered temperature excitation occurred always and 

 became maximal. Therefore one of the features which 

 characterise the animal nerve is found also in the conduct- 

 ing-tissue of the plant. 



Multiple Excitation by Constant Current 



A very striking result of the passage of a constant current 

 is the production of multiple responses in certain rhythmic 

 tissues. Thus the non-ganglionated preparation of the 

 apex of the frog's heart is under ordinary conditions 

 quiescent, but on the passage of a constant current it 

 breaks forth into a rhythmic series of excitations. 



In a subsequent chapter it will be shown that certain 

 vegetable tissues exhibit multiple responses. The pulvinus 

 of the leaflet of Biophytum is multiple-responding and 

 behaves in many respects like the cardiac tissue. Now 

 on maintaining a constant current of certain intensity 

 through the petiole, the kathode being placed on a 

 pulvinus, the particular leaflet will be found to execute 

 a series of pulsatory movements. 



Of still greater interest is the indirect effect of such 

 stimulation. A particular leaflet of Biophytum is attached 

 to the recording lever. A constant current is sent for a 

 short time through the petiole, the kathode being at a 

 distance of 10 mm. from the leaflet. The leaflet responded 

 to the excitation caused by kathode-make ; the response 

 here was due to the excitation transmitted through the 

 distance of 10 mm. The first part of fig. 124 gives four 



