

POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 67 



the wave of increased tension being transmitted across its 

 area, whereas the wave of true excitation is arrested. 



But the hydrostatic disturbance itself was caused by the 

 excitatory contraction of the distant point. The abolition of 

 the excitability of an intermediate point did not, as we have 

 seen, block the hydrostatic wave. If now the stimulator be 

 brought nearer, and placed over the strongly anaesthetised 

 area, the expulsion of water dependent on true excitation 

 can no longer take place. On doing this, therefore, we find 

 that neither the true excitatory negative, nor its consequent 

 hydrostatic positive effect, is exhibited at the responding 

 point. Response is thus totally abolished. 



We thus see that incident stimulus gives rise in the plant 

 to two distinct responsive expressions. In that which we 

 shall consider first namely, the direct, or true excitatory 

 effect there is an expenditure of energy, which is indicated 

 by a contraction, negative turgidity-variation, mechanical 

 fall, and galvanometric negativity. In the second, or indirect, 

 ~6T these two effects, we have the opposite of all these. That 

 is to say, we have here an increase of internal energy, expan- 

 sion, positive turgidity-variation, erection of leaf, and galvano- 

 metric positivity. The galvanometric negativity, due to 

 negative turgidity-variation, is generally speaking of much 

 greater intensity than the galvanometric positivity, due to 

 positive turgidity-variation. Hence, when the two effects 

 act on a tissue in rapid succession, that of electro-negativity 

 masks the positive. The wave of increased hydrostatic tension, 

 by which the indirect effect of stimulus is transmitted, has a 

 greater speed of transmission than that of true excitation. It 

 may be transmitted even across tissues of which the excita- 

 bility has been depressed or abolished, whereas the trans- 

 mission of true excitation is arrested by the intervention of 

 such a physiological block. 



The occurrence of these opposed effects of galvanometric 

 negativity and positivity has long been regarded as a pheno- 

 menon of a highly perplexing nature. It was too hastily 

 assumed that wherever these opposed electrical changes took 



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