i8 RESPONSE IN THE LIVING AND NON-LIVING 



It must however be remembered that the response, being 

 a function of physiological activity of the plant, is liable 

 to undergo changes at different seasons of the year. 

 Each plant has its particular season of maximum 

 responsiveness. The leaf-stalk of horse-chestnut, for 

 example, exhibits fairly strong response in spring and 

 summer, but on the approach of autumn it undergoes 

 diminution. I give here a list of specimens which will 

 be found to exhibit fairly good response : 



Root. Carrot (Daucus Carota), radish (Raphanus 

 sativus). 



Stem. Geranium (Pelargonium), vine (Vitisvinifera). 



Leaf-stalk. Horse-chestnut (^Esculus Hippocas- 

 tanum), turnip (Brassica Napus), cauliflower (Brassica 

 oleracea), celery (Apium graveolens), Eucharis lily 

 (EucJiaris amazonica). 



Flower-stalk. Arum lily (Richardia africana). 



Fruit. Egg-plant (Solanum Melongend). 



Negative variation. Taking the leaf-stalk of turnip 

 we kill an area on its surface, say B, by the application 

 of a few drops of strong potash, the area at A being 

 left uninjured. A current is now observed to flow, in 

 the stalk, from the injured B to the uninjured A, as 

 was found to be the case in the animal tissue. The 

 potential difference depends on the condition of the 

 plant, and the season in which it may have been 

 gathered. In the experiment here described (fig. 6, a) 

 its value was -13 volt. 



A sharp tap was now given to the stalk, and 

 a sudden diminution, or negative variation, of cur- 

 rent occurred, the resting potential difference being 



