XIV PLANT RESPONSE 



Mimosa under continuous stimulation — Conductivity and excitability of 

 tissue diminished through incomplete protoplasmic recovery — Relatively 

 greater fatigue in a motile than conducting organ — Disappearance of the 

 motile excitability earlier than conductivity — Refractory period — Absence 

 of responsive effect when stimulus falls within refractory period . * . 103 



CHAPTER X 



THEORIES CONCERNING DIFFERENT TYPES OF RESPONSE 



The chemical theory of response — Insufficiency of the theory of assimilation 

 and dissimilation to explain fatigue and staircase effects — Similar 

 responsive effects seen in inorganic substances — Molecular theory — 

 When molecular recovery is complete, responses uniform : when incom- 

 plete, fatigue brought about by residual strain — Fatigue under con- 

 tinuous stimulation, in inorganic substance, in plant, and in muscle — 

 Staircase effect brought about by increased molecular mobility : examples 

 seen in inorganic substance, and in living tissues— No sharp line of 

 demarcation in the borderland between physical and chemical pheno- 

 mena — Molecular changes attended by changes of chemical activity — 

 Unequal molecular strain gives rise to a secondary series of crTemical 

 actions— Volta-chemical effect and by-products — Supposition that re- 

 sponse always disproportionately larger than stimulus, not justified — 

 Existence of three types : (1) response proportionate to stimulus; (2) 

 response disproportionately greater than stimulus; (3) response dis- 

 proportionately less than stimulus — Instances of stimulus partially held 

 latent : staircase and additive effects ; multiple response ; renewed 

 growth . . . . . . . . . . . .116 



CHAPTER XI 



EFFECT OF ANAESTHETICS, POISONS AND OTHER CHEMICAL 

 REAGENTS ON LONGITUDINAL RESPONSE 



Response modified by physiological change — Carbonic acid causes depression, 

 and transitory exaltation as after-effect — Gradual abolition of response in 

 hydrogen and restoration by access of air— Chemical agents cause con- 

 traction or relaxation of plant-tissue — Effect of alcohol causing temporary 

 exaltation of response followed by depression and protracted period of 

 recovery — Ether causes relaxation and temporary depression of response 

 —Explanation of anomalous action of ether on stimulated Mimosa leaf 

 — Abolition of response by hydrochloric acid — Response restored by 

 timely application of ammonia — Abolition of response by poisonous 

 reagent — Similarity of effect of chemical agents on the response of animal 

 and vegetable tissues . . . . . . . . . .129 



