PART III.

TROPISM IN PLANTS.

XXII.--THE BALANCED CRESCOGRAPH. PAGE. Principle of the Method of Balance--Compensating movement-- Growth-scale--Sensitiveness of the Crescographic Balance-- Effect of CO_{2}--Effect of anæsthetics 255

XXIII.--ON TROPIC MOVEMENTS.

Complexity of the problem--Contradictory nature of responses--Two classes of tropic responses--Longitudinal transmission of effect of stimulus--Transverse transmission of effect of stimulus--Modification of tropic curvature by conducting power of tissues and differential excitability of the organ 268

XXIV.--TROPIC CURVATURE WITH LONGITUDINAL TRANSMISSION OF EFFECT OF STIMULUS.

Dual impulses, positive and negative, caused by stimulus-- Direct and Indirect stimulus--Tropic effect of Indirect stimulation 271

XXV.--TROPIC CURVATURE WITH TRANSVERSE TRANSMISSION OF EFFECT OF STIMULUS.

Turgor variation under transverse transmission of stimulus-effect--Tropic responses of pulvinated and growing organs to unilateral stimulation--Direct unilateral stimulation--Indirect unilateral stimulation--Difference of effects induced by Direct and Indirect stimulation--Laws of tropic curvature 279

XXVI.--MECHANOTROPISM: TWINING OF TENDRILS.

Anomalies of mechanotropism--Effects of indirect and direct electric stimulation on growth of tendril--Effect of direct and indirect mechanical stimulus--Immediate and after-effect of stimulus--Inhibitory action of stimulus--Response of less excitable side of the tendril--Relative intensities of responses of upper and under sides of tendril of _Passiflora_--Negative curvature of tendril 288

XXVII.--ON GALVANOTROPISM.

Polar effects of electric current on growth--Effect of anode and cathode on growth 301

XXVIII.--ON THERMONASTIC PHENOMENA.

Effect of temperature--Different thermonastic organs--Two types of response: Positive and Negative--Effect of rise of temperature and of stimulus on thermonastic organs--Law of thermonastic reaction 305

XXIX.--ON PHOTOTROPISM.

Complexity of problem of phototropic reaction--Action of light--Positive phototropic curvature of pulvinated organs--Positive phototropic curvature of growing organs--Phenomenon of recovery--Immediate and after-effect of light on growth--Latent period of phototropic reaction-- Growth variation induced by flash of light from a single spark--Maximum positive curvature under continued action of light 313

XXX.--DIA-PHOTOTROPISM AND NEGATIVE PHOTOTROPISM.

Differential excitability of two halves of pulvinus of _Mimosa_--Transformation of positive to negative curvature--Tropic effect under sunlight--Negative phototropism of shoot and root 328

XXXI.--RELATION BETWEEN THE QUANTITY OF LIGHT AND THE INDUCED PHOTOTROPIC CURVATURE.

Effect of increasing intensity of light on pulvinated and growing organs--Effect of increasing angle--Effect of duration of exposure 338

XXXII.--THE PHOTOTROPIC CURVE AND ITS CHARACTERISTICS.

Summation of stimulus--General consideration--The general characteristic curve--Characteristics of simple phototropic curve--Variation of susceptibility for excitation in different parts of the curve--Effect of sub-minimal stimulus--The complete phototropic curves of pulvinated and growing organs--Limitation of Weber's law 346

XXXIII.--TRANSMITTED EFFECT OF PHOTIC STIMULATION.

Effect of light applied on tip of Setaria--Response of growing region to unilateral stimulus--Effect of simultaneous stimulation of the tip and the hypocotyl-- Algebraical summation of effects of direct and indirect stimuli 362

XXXIV.--ON PHOTONASTIC CURVATURES.

Phototropic response of anisotropic organs--Positive para-heliotropism--Negative para-heliotropism--Responses of pulvinated and growing organs to light 378

XXXV.--EFFECT OF TEMPERATURE ON PHOTOTROPIC CURVATURE.

Effect of temperature on excitability--Effect of temperature on conduction--Phototropic response of tendrils--Seasonal variation of phototropic curvature--Antagonistic effects of light and of rise of temperature 388

XXXVI.--ON PHOTOTROPIC TORSION.

Torsional response to light--Effect of different modes of lateral stimulation--Effect of differential excitability on the direction of torsion--Laws of torsional response-- Complex torsion under light--Advantages of the Method of Torsional Response--The Torsional Balance--Determination of the direction of stimulus 397

XXXVII.--RADIO-THERMOTROPISM.

Effect of infra-red radiation--Positive radio-thermotropism-- Dia-radio-thermotropism--Negative radio-thermotropism 410

XXXVIII.--RESPONSE OF PLANTS TO WIRELESS STIMULATION.

Effects of different rays of spectrum on growth--The wireless system--Mechanical and electrical responses of _Mimosa_ to Hertzian waves--Effect of wireless stimulation on growth of plants 416

XXXIX.--GEOTROPISM.

Direction of the stimulus of gravity--The Geotropic Recorder--Determination of the character of geotropic reaction--Theory of statoliths--Determination of the latent period--The complete geotropic curve--Determination of effective direction of stimulus of gravity--Algebraical summation of effects of geotropic and photic stimulus-- Analogy between the effects of stimulus of light and of gravity--Relation between the directive angle and geotropic reaction--Differential geotropic excitability 425

XL.--GEO-ELECTRIC RESPONSE OF SHOOT.

Electric response to direct and indirect stimulation-- Experimental arrangement for obtaining geo-electric response--Geo-electric response of the upper and lower sides of the organ--Method of Axial Rotation--Characteristics of geo-electric response--Physiological character of geo-electric response--Effect of differential excitability of the organ--Law determining the relation between angle of inclination and geotropic effect--Method of Vertical Rotation--Electric response through an entire cycle-- Relation between angle of vertical rotation and intensity of geo-tropic reaction 442

XLI.--MECHANICAL AND ELECTRICAL RESPONSE OF ROOT TO VARIOUS STIMULI.

Mechanical and electrical response to Direct stimulation-- Mechanical and electrical response to Indirect stimulation-- Effect of unilateral stimulation applied at the root-tip 461

XLII.--GEO-ELECTRIC RESPONSE OF ROOT.

Geo-electric response of the root-tip--Electric response in the growing region of root--Differential effect between the tip and the growing region--Geo-perception at the root-tip 467

XLIII.--LOCALISATION OF GEO-PERCEPTIVE LAYER BY MEANS OF THE ELECTRIC PROBE.

Principle of the method of electric exploration--The Electric Probe--Electric exploration of the geo-perceptive layer--Geo-electric reaction at different depths of tissues--Microscopical examination of the maximally excited layer--Influence of season on geo-electric response--Tests of insensitive specimens--Reaction at lower side of the organ--The Method of Transverse Perforation 478

XLIV.--ON GEOTROPIC TORSION.

Arrangement for torsional response--Algebraical summation of geotropic, and phototropic effects--Balance of geotropic by phototropic action--Comparative balancing effects of white and red lights--Effect of coal gas on photo-geotropic balance 503

XLV.--ON THERMO-GEOTROPISM.

Necessary conditions for geotropic curvature--Modifying influence of temperature on geotropic curvature--Magnetic analogue--Tropic equilibrium under varying intensities of stimulus--Effect of variation of temperature on geotropic torsion--Variation of apo-geotropic curvature under thermal change--Effect of variation of temperature on dia-geotropic equilibrium 509