THE INFLUENCE OF EXTERNAL AGENCIES 397 



of an internal injury, for the wound-reaction is only manifested after 

 a certain latent period. It is not impossible that the sudden bending might 

 modify metabolism, although in the case of the leaf of Dionaea the varia- 

 tions in the current produced by excitation begin before the leaf closes. 

 The resulting movements of water may, however, then aid in maintaining 

 differences of potential 1 . 



Dionaea muscipula. The leaf of this plant shows in the resting condition 

 a similar distribution of potential to that of an ordinary leaf, whereas after stimulation 

 pronounced disturbances occur according to Burdon-Sanderson and to Munk. The 

 former, using extremely delicate modes of investigation, found that a variation of the 

 current in the external circuit took place 0-04 of a second after the application of 

 a single weak induction-shock, whereas the resulting movement began only after 

 a latent period of a second, the closure of the leaf-lobes requiring 5 to 6 seconds for 

 completion at 2oC. If the shock is extremely weak, the electrical variation may be 

 produced without any movement resulting. Presumably the electrical response is an 

 indication of the commencement of chemical or other changes which, when completed , 

 lead to a movement. That this stimulatory action spreads rapidly is shown by the 

 speed of propagation of the electrical variation, for this occurs only 0-05 of a second 

 later at a point 10 mm. away, the velocity of propagation being therefore 200 mm, 

 per second. The progress and character of the electrical variation strongly resembles 

 that shown on animal objects 2 . 



A pulvinar thorn on the leaf of Mimosa pudica is strongly positive to the upper 

 surface of the pulvinus, and according to Kunkel 3 a marked electrical variation ensues 

 when the leaf is stimulated. 



Injuries produce pronounced electrical variations, and these possibly 

 initiate or at least indicate the commencement of the disturbances leading 

 to the wound-reaction. According to Hermann, Ranke, Velten, and 

 Kunkel the injured region usually becomes negative or more negative 

 towards the uninjured part. Hence an injured stem may yield a current 

 although none was shown when intact 4 . Indeed the current of injury 

 was the first one observed, for a considerable difference of potential often 

 exists between the injured and uninjured surfaces 5 . 



Not only is the injured surface of a previously quiescent stem negative to 

 uninjured regions, but also points on the latter near to the injury are negative 



affected. Cf. Velten, 1. c., p. 295 ; Haake, 1. c., p. 480 ; Hermann, Studien ii. d. Protoplasma- 

 stromung bei den Characeen, 1898, p. 72. 



1 A. Tompa (l.c., p. 116) denies Waller's statement (Proc. of the Physiol. Soc., 9. Nov., 1901 ; 

 Centralbl. f. Physiol., 1901, Bd. xv, p. 480) that local blows produce current-variations, but his 

 experiments are not conclusive. Cf. also Bose, Journ. of Linn. Soc. Botany, 1902, Vol. xxxv, p. 275. 



a A complete summary is given by Biedermann, 1. c., p. 455. 



3 Kunkel, I.e., 1878, p. n ; Dnbois, Centralbl. f. Physiol., 1899, Bd. xin, p. 699. 



* According to Tompa (Beiheft z. bot. Centralbl., 1902, Bd. xn, p. 117) a current of injury i& 

 perceptible on injured air -dried seeds. 



5 Internal currents may be present in a plant-organ although no external current can be led off r 

 whereas a resting muscle shows no internal currents. Cf. Biedermann, 1. c., p. 288. 



