PART I.

RESPONSE OF PLANT ORGANS.

I.--THE PROBLEM OF MOVEMENT IN PLANTS.

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Complexity of the problem--Effects of different forms of stimuli--Diverse responses under identical stimulus--Modification of response determined by intensity and point of application of stimulus, and tonic condition of organ--Response of pulvinated and growing organs--Necessity for shortening the period of experiment 1

II.--THE “PRAYING” PALM TREE.

Description of phenomenon--The Recording apparatus--Record of diurnal movement of the tree--Universality of tree movement--Cause of periodic movement--Periodic movement of trees, and diurnal variation of moto-excitability in _Mimosa pudica_--Relative effects of light and temperature--Physiological character of the movement--Transpiration and diurnal movement--Diurnal movement in inverted position--Effect of variation of temperature on geotropic curvature--Reversal of natural rhythm by artificial variation of temperature 5

III.--ACTION OF STIMULUS ON VEGETABLE TISSUES.

Different types of Response Recorders--Response of a radial organ--Response of an anisotropic organ--Response of pulvinus of _Mimosa pudica_--Tabular statement of apex time and period of recovery in different plants--Response of pulvinus of _Mimosa_ to variation of turgor--Different modes of stimulation 31

IV.--THE DIURNAL VARIATION OF EXCITABILITY IN _MIMOSA_.

Apparatus for study of variation of excitability--Uniform periodic stimulation--The Response Recorder--Effects of external condition on excitability--Effects of light and darkness--Effect of excessive turgor--Influence of temperature--Diurnal variation of excitability--Effect of physiological inertia 43

V.--RESPONSE OF PETIOLE-PULVINUS PREPARATION OF _MIMOSA_.

Effect of wound or section in modification of normal excitability--The change of excitability after immersion in water--Quantitative determination of the rate of decay of excitability in an isolated preparation--Effect of amputation of upper half of the pulvinus--Effect of removal of the lower half--Influence of weight of leaf on rapidity of responsive fall--The action of chemical agents--Effect of “fatigue” on response--The action of light and darkness on excitability 73

VI.--CONDUCTION OF EXCITATION IN PLANTS.

Hydro-dynamic _versus_ physiological theory of conduction of excitation--Arrest of conductivity by physiological blocks--Convection and conduction of excitation--Effect of temperature on velocity--Effect of season--Effect of age--Effect of dessication of conducting tissue--Influence of tonic condition on conduction--Effect of intensity of stimulus on velocity of transmission--Effect of stimulus on sub-tonic tissues and tissues in optimum condition--Canalisation of conducting path by stimulus--Effect of injury on conductivity 97

VII.--ELECTRIC CONTROL OF EXCITATORY IMPULSE.

Method of conductivity-balance--Control of transmitted excitation in _Averrhoa bilimbi_ by electric current--‘Uphill’ transmission--Transmission ‘downhill’--Electric control of nervous impulse in animal--Directive action of current on conduction of excitation--Effects of direction of current on velocity of transmission in _Mimosa_--Determination of variation of conductivity by method of Minimal Stimulus and Response--Influence of direction of current on conduction of excitation in animal nerve--Variation of velocity of transmission--After-effects on Heterodromous and Homodromous currents--Laws of variation of nervous conduction under electric current 107

VIII.--EFFECT OF INDIRECT STIMULUS ON PULVINATED ORGANS.

Conduction of excitation--Dual character of the transmitted impulse--Effect of distance of application of stimulus--Periods of transmission of positive and negative impulses--Effects of Direct and Indirect stimulus 135

IX.--MODIFYING INFLUENCE OF TONIC CONDITION ON RESPONSE.

Theory of assimilation and dissimilation--Unmasking of positive effect--Modification of response under artificial depression of tonic condition--Positive response in sub-tonic specimen 141