88 RESEARCHES ON IRRITABILITY OF PLANTS 



dots. It will be seen that there is an abolition of 

 excitability, stimuli which were formerly effective becoming 

 now quite ineffective. 



I next tried to find out whether it were possible to restore 

 the lost excitability by artificial means. Guided by the 

 consideration that glycerin has the power of abstracting 

 water, I applied a drop of strong glycerin to the pulvinus. 

 It will be noted that this had the effect of quickly restoring 

 the motile excitability of the pulvinus. The two responses 



Fig. 45. — Abolition of motile excitability of pulvinus by absorp- 

 tion of water. Note prolongation of period of recovery and 

 ineffectiveness of stimuli applied at moments marked with 

 thick dots. Subsequent restoration of excitability by applica- 

 tion of glycerin. 



after the application of glycerin are practically similar 

 to the normal responses at the beginning of the series. I am 

 unable to say whether the restoration of excitability was 

 here due entirely to the abstraction of water. One might 

 think that continuous abstraction of water would induce 

 a continuous variation of excitability — probably an enhance- 

 ment reaching a maximum followed by a decline. I find, 

 however, that the application of glycerin restores the normal 

 excitability, and that generally speaking this remains 

 constant even under the continued action of the reagent. 

 This is a fortunate circumstance for those particular investi- 



