XIII.--EFFECT OF VARIATION OF TURGOR AND OF TENSION ON GROWTH. Response to positive variation of turgor--Method of irrigation--Effect of artificial increase of internal hydrostatic pressure--Response to negative variation of turgor--Method of plasmolysis--Effect of alternative variations of turgor on growth--Response of motile and growing organs to variation of turgor--Effect of external tension 188 XIV.--EFFECT OF ELECTRICAL STIMULUS ON GROWTH. Effect of intensity--Effect of continuous stimulation--Continuity between ‘incipient’ and actual contraction--Immediate effect and after-effect 195 XV.--EFFECT OF MECHANICAL STIMULUS ON GROWTH. Effect of mechanical irritation--Effect of wound 200 XVI.--ACTION OF LIGHT ON GROWING ORGANS. Method of experiment--Normal effect of light--Determination of the latent period--Effect of intensity of light--Effect of continuous light--Effects of different rays of the spectrum 205 XVII.--EFFECT OF INDIRECT STIMULUS ON GROWTH. Mechanical and electrical response to Indirect Stimulus--Variation of growth under Indirect Stimulus--Effects of Direct and Indirect Stimulus 213 XVIII.--RESPONSE OF GROWING ORGANS IN STATE OF SUB-TONICITY. Theory of assimilation and dissimilation--Unmasking of positive effect--Modification of response under artificial depression of tonic condition--Positive response in sub-tonic specimen--Abnormal acceleration of growth under stimulus--Continuity between abnormal and normal responses--Positive response to sub-minimal stimulus 219 XIX.--RESUMPTION OF AUTONOMOUS PULSATION AND OF GROWTH UNDER STIMULUS. Resumption of pulsatory activity of _Desmodium_ leaflet at standstill--Renewal of growth under stimulus--General laws of effects of Direct and Indirect Stimulus 227 XX.--ACTION OF LIGHT AND WARMTH ON AUTONOMOUS ACTIVITY. The Oscillating Recorder--Record of pulsation of _Desmodium gyrans_--Effect of diffuse light in diminution of amplitude and reduction of diastolic limit of pulsation--Antagonistic action of warmth in reduction of systolic limit 233 XXI.--A COMPARISON OF RESPONSES IN GROWING AND NON-GROWING ORGANS.