354 CHAP. XXXI. INCLINATION AND EXCITATION 



sensitive cells ; first, the pressure exerted by the particles, 

 and, second, the irritability of the ectoplasmic layer pressed 

 upon by the particles. As regards the first, the effective 

 pressure exerted by the particles is proportional to the sine of 

 the angle of inclination ; but in regard to the second, the 

 irritabihty of the ectoplasmic layer may not be the same 

 throughout the length of the cell, but be greater towards the 

 apical end. At the smaller angle of incHnation, say to the 

 right, the statoUths, originally at the base of the cell, accumu- 

 late at the right-hand lower corner of the cell, a portion of the 

 basal end of the cell being thus subjected to pressure. When 

 the angle of inclination is increased, the statoliths come to lie 

 along the whole lateral length of the cell, extending to the 

 apical end. The relatively greater excitation with increasing 

 angle of inclination may therefore be explained on the 

 assumption that the excitability of the ectoplasm is greater 

 towards the apex ; facts will be given which appear to lend 

 support to this view. 



Excitatory Reaction at 45° and 135° 



Controversy has arisen over the question as to whether 

 the intensity of geotropic excitation is the same or different 

 at the angles of inclination 45° and 135°. The effective 

 pressure exerted by the stimulating particles in the cells is 

 the same at the two angles ; the only difference in the tw^o 

 cases is the collection of the particles at the basal end of the 

 cells at 45°, and at the apical end at 135°. Czapek found 

 that the effective stimulus of gravitation is greater when the 

 organ is held at 135° than when it is held at 45°, though 

 his results have not been accepted by others. 



I carried out investigations on the subject, employing 

 the method of electric response. Allowance was made for 

 any possible change in excitability brought on by fatigue. 

 This was secured by conducting the experiments in the 

 following sequence of observation : (i) reaction at 45° ; 

 (2) reaction at 135° ; and (3) reaction once more at 45°. 

 The comparison of the first and the third responses showed 



