6.S8 GENERAL CONDITIONS OF PLANT-LIFE. 



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 

 ce'.l 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 become completely mixed by diffusion-currents. This behaviour, which 

 must certainly produce electromotive effects, has not hitherto been investigated with 

 this object \ 



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 phenomena 

 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 therefore 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 

 vegetation has at present, like the whole subject, not been investigated scientifically. 

 The destructive discharges of atmospheric electricity which are effected through 

 trees by means of flashes of lightning"^, at least show that smaller differences of 

 electrical equilibrium between the air and earth may also be equalised by means 

 of plants*. 



^ Sachs, Ueber saure, alkalinische, und neutrale Reaction der Siifte lebender Pflanzen ; Bot. Zeit. 

 1862, No. 33. 



^ [Becquerel thought that the evaporation from leaves forms an upward current of vapour which 

 acted as a conductor to electricity. In this way, by destroying the necessary electrical conditions, 

 he thought forests tended to dissipate hail-clouds. Mdm. de I'lnst. vol. XXXV, pp. 806, 807. — Ed.] 



^ [The disruptive effect of lightning upon trees is probably due to the sudden conversion of 

 moisture into steam. See Osborne Reynolds, Proc. Phil. Soc. Manch. 1874, p. 15. — Ed.] 



* [Edwin Smith (Chemical News, Dec. 17, 1869) has detected constant currents of electricity 

 passing in certain diiections in plants, as follows : — In a cut piece of leaf-stalk (rhubarb) from the 



