THE INFLUENCE OF EXTERNAL AGENCIES 395 



surface. Haake even found this to be the case in the internodal cells of 

 Nitella and the same may apply to large non-cellular Algae like Caidcrpa, 

 although, to judge from the absence of ' blaze ' currents from most Algae, 

 they are comparatively incapable of electrical response *. 



There is, however, no constant rule for the distribution of the surface 

 potential even under homogenous and regular external conditions. Sym- 

 metric points on a leaf or stem are usually isopotential 2 , while judging 

 from the direction of the current in the external circuit the midrib is 

 positive to the lamina. Nevertheless exceptions occur 3 , as is also the 

 case when the potentials of old and growing zones are contrasted, while 

 in the latter case changes commonly occur during development. Although 

 electrical disturbances were known to occur during the rapid closure of the 

 leaf-lobes of Dionaea> and as the result of injury and of changes of tempera- 

 ture, Haake was the first to show that they always take place when the 

 metabolism is sufficiently modified by changes in the external conditions. 



The removal of oxygen 4 always causes a certain electrical disturbance. 

 When the entire object is in hydrogen the galvanometer deflection is 

 usually lessened and is sometimes reversed, whereas the local absence 

 of oxygen produces an increased deflection, independently of whether the 

 negative or positive region is placed in the hydrogen. Although deviations 

 are often shown 5 , the results indicate the prominent part played by aerobic 

 respiration in the production of electricity, although the latter can still be 

 formed by the intramolecular respiration occurring when oxygen is absent. 

 No definite causal relationships are revealed by these facts, and the com- 

 plicated nature of respiration in general renders it hardly surprising that 

 on the return of a still living plant to air, the original distribution of 

 potential may not be restored, and that in the continued absence of oxygen 

 the galvanometer may show a varying deflection. In both cases the 

 transition to the new conditions produces pronounced temporary deflections 

 of the galvanometer. 



Temperature. The changes of current produced by rises or falls of 

 temperature in objects kept in air saturated with moisture are, in part 

 at least, due to quantitative and possibly qualitative alterations of respira- 

 tion and metabolism, although alterations of resistance and other factors 



1 Waller, Journ. of Linn. Soc., 1904, Vol. xxxvn, pp. 32, 40. 



2 On the isopotentials of leaves cf. Kunkel, 1. c. ; Haake, 1. c., p. 483 ; Munk, 1. c., p. 37. 



3 Cf. Kunkel, 1. c., 1878, p. 2 ; Haake, 1. c., p. 458 ; Klein, 1. c., p. 336. 



* Haake, 1. c., p. 467. On some researches on the effect of the removal of oxygen on animals 

 cf. Biedermann, I.e., p. 402. The changes of potential are not due to the gaseous movements due 

 to production and consumption. 



5 Haake (1. c., p. 470) observed an increased deflection when the seedling of Vicia Faba was 

 placed in hydrogen, possibly because during the intramolecular respiration of this plant as much, or 

 in the case of the cotyledons even more, carbon dioxide is produced than during normal oxygen 

 respiration. 



