ELECTRO-PHYSIOLOGY CHAP. 



men (a seedling of Pisum 14 days old), the initial deflection of 

 + 5 degrees rose on leading off from collar of root and tip of stalk 

 to + 5 7 degrees, after driving off the oxygen from the root and 

 lower part of the stem, falling again with a fresh supply of air to 

 + 1 4 degrees. With uninterrupted supply of air, the same effect 

 results from local changes in respiratory activity due to rise or 

 fall of temperature in the plant, near one or the other electrode. 



The assimilatory process seems, from Haake's experiments, 

 also to contribute to the differences of potential exhibited by 

 green leaves. The arrest by darkness of the decomposition of 

 C0 2 regularly produces a diminution of the initial current. " If 

 the normal conditions are restored (by illumination), the former 

 potential reasserts itself; but its magnitude is permanently 

 affected, and becomes either less or greater." Leaves that contain 

 no chlorophyll (petals of flowers) show no change of electrical 

 response when they are deprived of light. The most important 

 fact in these observations is the existence of an electrical P.D. 

 between the cells, or, strictly speaking, tracts of cells, in a 

 vegetable organ or entire plant, which differ in their chemical 

 constitution. 



The electromotive reactions of vegetable organs (for the most 

 part very inconspicuous as compared with the corresponding- 

 manifestations in animal tissues) have attracted much more 

 attention since the discovery of the striking manifestation in 

 excitable plants, as first pointed out by Burdon-Sanderson, when he 

 showed that the excitatory movements of the leaf of Dioncea musci- 

 pula are accompanied by highly characteristic alterations of the 

 original P.D. between upper and under surface (6). 



The subject is best introduced by describing the organisation 

 and structure of the parts of plants involved, as well as the nature 

 and causes of their excitatory movements. 



The general habit of growth in Dioncea muscipula is shown in 

 Fig. 139, which at the same time gives the method employed by 

 Munk (to whom we owe an admirable work on the electro- 

 motive action and excitatory movements of this plant, 7) for 

 setting up the specimens he investigated, so as to lead off from 

 the leaves as conveniently as possible. 



The leaf, which is from 2 to 12 cm. long in the full-grown 

 plant, is divided externally into three sections the winged leaf- 

 stalk, its unwinged part, and the lamina of the leaf. This last 



