vi ELECTROMOTIVE ACTION IN VEGETABLE CELLS 5 



approximately recovered its former strength. The same reaction 

 occurred in seedlings of Pisum sativum on leading off from the 

 collar of the root and the stem, where Hermann (3) had pre- 

 viously found a normal strong current, the root being negative to 

 the body (i.e. the cotyledons). The E.M.F. often exceeded ^ 

 Dan. Johannes Muller-Hettlingen (3), who studied this effect 

 more closely at Hermann's request, formulated the law as follows : 

 When one of the leading-off electrodes is persistently applied to 

 the cotyledons, while the other leads off successively from points 

 of the seedling above or below the cotyledon, there is always a 

 current directed from the electro-positive seed husk, or cotyledon, 



FIG. 137. 



FIG. 138. 



to all other electro -negative parts of the seedling, its E.M.F. 

 being less in proportion as the exploring electrode is nearer the 

 cotyledon, above or below it. Fig. 138 gives a schema of this 

 reaction. 



Haake occasionally found reversal, or augmentation, instead of 

 diminution, of the original current when respiration was inter- 

 rupted. " Such parts of plants as naturally exhibit marked 

 differences in respiration yield excessively strong currents, e.g. 

 the reproductive organs of flowers, on leading off from pistil or 

 anther, and flower-stalk." In such cases Haake obtained deflec- 

 tions of 50-80 degrees on the capillary electrometer, while in 

 green leaves the total effect is only 1520 degrees. 



The P.D. is also, comparatively speaking, very marked when 

 the respiration of a plant is checked at one electrode only, by 

 cutting off the supply of oxygen, which Haake effected by en- 

 closing seedlings of Pisum or Faba in a double tube, and replacing 

 the air by hydrogen on one side only (Fig. 137). In one speci- 



