ELECTRO-PHYSIOLOGY CHAP. 



small, owing to the high resistance. In the majority of cases the 

 " longitudinal- transverse " current in divided plant-stalks dimin- 

 ishes rapidly, and may even be reversed. Hermann (who refers 

 these currents, by analogy with the currents of muscle and nerve, 

 to the immediate contact of chemically altered dying and normal 

 plasma in the injured cells) explains this by the individual death 

 of the latter, as Engelmann has said of smooth muscle-cells. " If 

 the opened, or otherwise injured, protoplasmic tubes were con- 

 tinuous throughout the length of the tissue, like the fibres of 

 nerve and muscle, the process of death would creep forward, and 

 the cross-section be permanently negative to the surface of the 

 plant. Most of the cells which contain the protoplasm are, 

 however, short, albeit drawn out longitudinally, and thus the 

 negativity of a cross-section is transitory, although a further 

 section exhibits fresh activity " (I.e.). 



Much greater interest attaches to the electrical reactions 

 which may appear in certain organs of plants that are perfectly 

 uninjured. The name of Burdon- Sanderson is foremost in the.se 

 researches. His admirable observations on the excitable leaf of 

 Dioncca muscipula are by far the best contribution to the 

 subject. Later on we shall have to study these in detail ; here 

 it need only be said that differences of potential are also found in 

 the totally uninjured leaf, particularly between upper and under 

 surface, and exhibit perfectly regular variations during the ex- 

 citatory movements of the plant. 



A. J. Kunkel (4), working under Sachs' direction, concluded, 

 from the green foliage-leaves of different kinds of plants, that (on 

 leading off with unpolarisable electrodes, under uniform conditions) 

 the veins of the leaf were positive to its green surface. " The 

 stout mid-rib is weakly positive to the finer lateral veins ; in the 

 latter the junction of two veins is a highly positive point." 

 According to Kunkel, the sign of this P.D. depends essentially 

 upon the state of imbibition at the leading-off contacts at the 

 moment, since every point that has been moistened for some 

 time is at first positive to points that have been more recently 

 wetted. 



And if these experiments indicate i;he great significance of 

 the distribution, or movement, of water in vegetable organs, with 

 reference to their electromotive activity, the same appears still 

 more plainly from Kimkel's experiments as to the effects of injury 



