CONTENTS XXI 



PAGE 



The * starch- sheath,' the perceptive layer — Evidence of in- 

 sensitive specimens — The electric, geotropic and microscopic 

 tests — ^Duplication of geo-perceptive layer in shoot of Calendula. 326 



CHAPTER XXXI 



RELATION BETWEEN ANGLE OF INCLINATION AND 

 GEOTROPIC EXCITATION 



Excitatory geotropic reaction at 45° and 90° — Geotropic excita- 

 tion at various angles — Excitatory reaction at 45° and 135° — 

 Greater geotropic excitability at apical than at basal end of 

 sensitive statocysts . . . . . . . .348 



CHAPTER XXXn 



THE CRITICAL ANGLE FOR GEOTROPIC EXCITATION 



Excitation disproportionately lower at smaller than at larger angles 

 of inclination — Determination of the critical angle — Method of 

 alternate inclination to right and to left — The effect of repetition 

 in lowering the critical angle . . . . . -357 



CHAPTER XXXni 



THE RESPONSE OF THE ROOT TO DIFFERENT STIMULI 



Irritable root-tip separate from responding growing region — ^Nlechani- 

 cal response to unilateral stimulation of root-tip — Response to 

 direct unilateral stimulation of growing region — Electric re- 

 sponse to indirect stimulation — Geo-electric response of root-tip 

 — Electric response in the growing region — Additive action-cur- 

 rent at the tip and at the growing region — Geo-perception at the 

 root-tip — Difference in the geotropic response of shoot and root — 

 Difference between effects of geotropic and photic stimulation . 365 



CHAPTER XXXIV 



THE MECHANISM OF THE TWINING STEM 



Characteristic response of anisotropic organs — Preliminary adjust- 

 ments — Autonomous torsion and circumnutation — Rates of 

 circumnutation at different hours of day — Torsional rotation 

 round a vertical axis — Torsional activity of different internodes 

 — Contact-stimulus and twining — Method of optical magnifica- 

 tion for investigation of torsional response — Automatic Recorder 



