746 PLANT RESPONSE 



From such considerations it may perhaps appear not very 

 far-fetched to regard a plant as possessed of a diffuse heart. 



With special reference to the effect of drugs on plant and 

 animal tissues, we find the identity of phenomena similarly 

 impressive. This is exemplified in both cases by their action 

 not only on ordinary contractile tissues, but on rhythmic 

 tissues also. Thus it is only necessary to mention such 

 facts as that anesthetics, like the vapours of ether and 

 chloroform, induce a transient abolition of excitability, with 

 abolition of response, in both animal and vegetable ; that 

 this excitability, with its concomitant response, is gradually 

 restored in either case on blowing off the applied vapour ; and 

 that poisonous reagents, on the other hand, induce a permanent 

 abolition of all response. The action of these and other 

 chemical agents has already been described in some detail. 



In the case of rhythmic response, again, a like parallelism 

 was found to exist, as between the effects of drugs on plant 

 and animal tissues respectively ; and this parallelism was 

 further shown to extend through a wide range of phenomena. 

 A remarkable instance was seen in the antagonistic effects 

 on responsive rhythmic tissues of the actions of acid and 

 alkali. Acid, when applied to cardiac muscle, induces a 

 diastolic standstill, whereas the effect of alkali is exactly the 

 opposite, a standstill, namely, of systolic contraction ; and 

 the standstill induced by either of these is found to be 

 counteracted by the application of the other. Now, I have 

 shown that the effects of acid and alkali on the rhythmic 

 tissues of Desmodium are similarly antagonistic. Thus, dilute 

 hydrochloric acid induced arrest of pulsation in the diastolic, 

 or relaxed, position, in the motile organ of Desmodium ; 

 whereas, with solution of sodium hydrate, the induced arrest 

 was of systolic contraction. Moreover, when arrest in its 

 own particular position had been brought about by either of 

 these reagents, its effect was neutralised by the application 

 of the other (p. 353). The same effects were found again 

 curiously reproduced in the case of the autonomous response 

 of growth. Here, the application of acid induced an arrest 



