VELOCITY OF TRANSMISSION OF EXCITATION 445 



This assumption, that there could be nothing in common 

 between the transmission of excitatory impulses in plant and 

 animal, was thought to derive support from Pfeffer's experi- 

 ment on the effect of anaesthetics on conduction in Mimosa. 

 The anaesthetisation of the pulvinus is found to abolish its 

 motile excitability. The effect of strong stimulus was never- 

 theless found by Pfeffer to be transmitted across the anaesthe- 

 tised area, giving rise to the depression of leaves beyond. It 

 was natural to infer from this that, as the motile excitability 

 of the pulvinus was abolished by the anaesthetic, so must 

 the protoplasmic conductivity also have been abolished. It 

 was therefore inferred that unlike the conduction of stimulus 

 in animal tissues, where such transmission is known to take 

 place by the propagation of protoplasmic changes the ap- 

 parent conduction of excitation in a plant was purely hydro- 

 mechanical. 



But I have shown elsewhere, and shall demonstrate again 

 in Chapter XXXIII. by different means, that though excita- 

 bility and conductivity are related phenomena, yet the varia- 

 tion of the one is not necessarily identical with that of the 

 other. Thus a certain degree of anaesthetisation may be 

 sufficient to induce arrest of motile excitability, and yet may 

 not always abolish conductivity. 1 



Another objection which has been urged against the 

 theory of the transmission of protoplasmic changes through 

 the plant is based on certain experiments of Haberlandt. In 

 these the excitation in Mimosa is said to have been propa- 

 gated over dead tracts of the petiole, these portions having 

 been killed by scalding, But it is extremely difficult to 

 ensure the death of interior tissues by such means as super- 

 ficial scalding. I have found that a portion of a plant tissue 

 which had been subjected locally to the action of boiling 

 water afterwards exhibited signs of true excitatory electrical 

 response. It is only by prolonged immersion in boiling water 

 that the electrical response is totally abolished. Only after 

 such treatment, therefore, can one be quite "sure that the 



1 Bose, Plant Response, pp. 227-229. 



