LOCALISATION OF GEO-PERCEPTIVE LAYER 



485 



was the shoot of Bryophyllum , one contact being made with 

 the side of the stem, and the other with an indifl"(irent 

 point on the leaf which was always held vertical. In a 

 particular experiment, the probe was introduced into the 

 stem through O-l mm. and a feeble galvanometric negati- 

 vity was induced as the wound-effect. After an interval of 

 ") minutes, thie attained a steady value of-l/i divisions. 

 On the rotation of stem through +90°, the point A was 

 al)ove and a very much larger deflection of - <S2 divisions was 

 <>l)tained, being the result of summation of wound and geo- 

 electric effects. On restoration of the plant to vertical posi- 

 tion the geo-electric reaction disappeared, leaving the persis- 

 tent wound reaction of -15 divisions unchanged. The true 

 geo-electric reaction at a point 0*4 mm. inside the stem was 

 thus -67 divisions which is the difference between - 82 and 

 -15 divisions. I obtained in this manner the excitatoiy 

 reactions at different layers of the organ. The following 

 table gives true values of geo-electric reaction at different 

 layer.< of the stem as the probe entered it by steps of 

 0*4 mm. 



TABLE XL. — SHOWINO THE OEO-ELECTKIC EEAOTION AT DIFFERENT 



DEPTHS OF THE ORGAN {Bryophyllum). 



The results given above, typical of many others, show 

 that there is a definite layer in the tissue which undergoes 



