304 RESEARCHES ON IRRITABILITY OF PLANTS 



phenomena of arrest and revival are easily observable in 

 the record. 



The question next arises whether any theory can be 

 suggested as to the cause of this arrest. A possible explana- 

 tion might lie in regarding the cut or sudden ligature as 

 intense forms of stimulation, whose effect is somewhat 

 persistent rather than instantaneous. We have further 

 to suppose that this intense stimulation is conducted by 

 the intervening petiolule. We have seen, moreover, that 

 the leaf of Mimosa under prolonged stimulation, after a 

 preliminary excitatory contractile movement, assumes a 



Fig. 149. — Arrest of pulsation of Desmodium by a cut applied at 

 moment marked by first arrow. Pulsation was revived by 

 electric shock applied at moment marked by second arrow. 



relaxed position indicative of over-stimulation and fatigue. 

 After the lapse of a requisite time, however, the leaf 

 regains its sensitiveness. In the case of the Desmodium 

 leaflet a similar effect might conceivably be induced 

 by the transmission of intense excitation from the stim- 

 ulated cut or ligatured end. This question of the effect 

 of ligature is admittedly one of great difficulty, even 

 in the case of the cardiac tissue. The explanation here 

 offered, as applying to the Desmodium leaflet, may be taken 

 as suggestive and more or less tentative. Such an idea 

 presupposes that the intervening petiolule contains some 

 conducting-tissue by which excitation may be transmitted. 

 In any case, the question as to the power of the petiolule to 



