120- BIOLOGY. [Book ii. 



exterior thermometrio variations, and consequently, they may 

 be hotter or colder than the exterior medium. 



Electricity seems to exercise very little influence upon the 

 nutritive movement of plants. Feeble constant currents, small 

 sparks of induction, have no apparent effect either upon the 

 movement of the protoplasm, or upon that of the mobile leaves. 

 A too powerful current, a spark too strong, causes either the 

 arrest of the protoplasm or that of the tissue. Thirty Grove 

 elements instantly stop the protoplasmic movement. 



As to the electric state of the tissues, it is curious to observe 

 in the plants phenomena very analogous to those which have 

 been observed in the nerves and muscular fibres of animals, and 

 have served as a basis for "many theories. In effect, in a cut 

 stem, there is a current from the surface of the stem to the 

 centre of section.^ The electric currents, which, without doubt, 

 result from the chemical assimilative and dis-assimilative reac- 

 tions of nutrition, are not peculiar to such and such a vegetal 

 or animal tissue. There again the two organic kingdoms touch 

 and intermingle, 



^ Buff, Annal. der Chimie und Pharmacie, 1854, Band 89. Jurgensen, Stu- 

 dien des Physiologisches Instituts zu Breslau, 1861, Heft I. — Heidenhain, Hid., 

 1863, Heft II. 



[Note. — ^A French metre is equal to 39^?^ English inches, or 

 to rather more than a yard. The small g occasionally occurring 

 indicates gramme ; the small m, metre ; the small mm a millimetre, 

 — Teanslatoe.J 



