768 
GENERAL CONDITIONS OF PLANT-LIFE. 
Sect. 9. — Electricity ^ The chemical processes within the cells of a plant, 
the molecular movements connected with the growth of the cell-wall and protoplasm, 
and the internal changes on which the activity of the protoplasm depends — whether 
exhibited in the formation of new cells or in movements of rotation — are probably 
connected with disturbances of the electrical equilibrium, although no actual em- 
pirical proof of this has yet been obtained. The fluids with different chemical pro- 
perties in adjoining cells, the diffusion of salts and of assimilated compounds from 
cell to cell, and their decomposition, must also bring electromotive forces into 
play; but even this has not yet been observed directly. Even the electrical currents 
which must no doubt be set up by the evolution of oxygen from cells containing 
chlorophyll, by the formation of carbon dioxide in growing organs (as in seed- 
lings), and by the transpiration of land-plants — although investigated by a few 
physicists — has not yet been actually established or accurately determined. Accord- 
ing to Buff's careful observations, which have been confirmed by Jiirgensen and 
Heidenhain, the internal tissue of land-plants is always electro-negative to its 
strongly cuticularised surface ; the surface of roots, saturated with sap (like a trans- 
verse section of the tissue), is also electro-negative to the surface of the stems and 
leaves. If a plant or a cut part of a plant is placed, with the necessary precautions, 
in the circuit of a very sensitive galvanometer, a current passes from the external 
surface to the cut surface or to the surface of the root ; this is in consequence of 
the contact of the cell-sap of the surface of the root or of a cut surface with the pure 
water employed to complete the circuit. The alkaline fluids of the thin-walled 
phloem of the fibro-vascular bundles are surrounded by the acid fluids of the paren- 
chyma, and diffusion-currents doubtless exist between them. These must certainly 
produce electromotive effects, but hitherto no investigations have been made on this 
subject^. 
The leaves and branches of plants present a large surface to the air ; and 
the tissue of the whole plant is permeated with electrolytic fluids. These con- 
ditions appear to adapt plants to be the medium for equalising electrical differences 
between the earth and air by means of currents traversing the plant. Since the 
electrical tension of the air is generally different from that of the earth, and the 
relationship of the two is constantly varying with changes of weather, it may be 
assumed that in all probability constant electrical interchanges are going on through 
the agency of plants^. Whether these have a favourable effect on the processes of 
^ Villari, Pogg, Ann. 1868, vol. 133. p. 425. — Jiirgensen, Studien des phys. Inst, zu Breslau, 1861 ; 
Heft I, p. 38 et seq. — Heidenhain, ditto 1863, Heft 2. p. 65. — Brücke, Sitzungsb. der Wien. Akad. 
1862. vol. 46. p. I. — Max Schultze, Das Protoplasma der Rhizopoden ; Leipzig 1863, p. 44. — Kühne, 
Untersuchungen über das Protoplasma, 1864, p. 96. — Cohn, Jahresber. der schles. Ges. für vater- 
landische Cultur, 1861 ; Hefti. p. 24.— Kabsch, Bot. Zeit. 1861, p. 358. — Riess, Pogg. Ann. vol. 69. 
p. 288. — Buff, Ann. der Chem u. Pharm. 1854, vol. 89. p. 80 et seq. — [J. Ranke, Untersuchungen 
über Pflanzenelektricität, Akad. der Wissen. München, Math. -Phys. Klasse, July 6, 1872. — Kunkel, 
ueb. elektromotorische Wirkungen an unverletzten Pflanzentheilen, and Ueb. einige Eigenthümlich- 
keiten des electrischen Leitungsvermögens lebender Pflanzentheile, Arb. d. bot. Inst, in Würzburg, 
II. I, 2, 1878-9. 
^ Sachs, Ueber saure, alkalinische, und neutrale Reaction der Säfte lebender Pflanzen ; Bot. Zeit. 
1862, No. 33. 
^ [Becquerel thought that the evaporation from leaves forms an upward current of vapour -which 
