igo LIFE AND WORK OF SIR JAGADIS C. BOSE 



deflection show the state of irritation of every layer of cell 

 throughout the organ. Holding the stem vertical, Bose 

 sent his exploring probe step by step across the organ and 

 found no sign of local excitation. The passage of the probe 

 itself, it is true, causes a slight irritation, but this is reduced 

 to a minimum by making the probe excessively fine and by 

 making the passage of the probe very slow. 



The case will be very different w r hen the stem is dis- 

 placed from the vertical to a horizontal position. The 

 geotropically sensitive layer now perceives the stimulus 

 and becomes the focus of irritation ; the state of excitation 

 is, as explained before, detected by negative electric response 

 exhibited by the galvanometer, and the electric variation 

 would be most intense at the perceptive layer itself ; the ex- 

 citation at the perceptive layer will irradiate into the neigh- 

 bouring cells in radial directions with intensity diminishing 

 with distance. Hence the intensity of responsive electric 

 change will decline in both directions outwards and inwards. 



The distribution of the excitatory change, initiated at 

 this perceptive layer and irradiated in radial directions, is 

 represented in the right hand of Fig. 23 (p. 158) by the depth 

 of shading, the darkest shadow being on the perceptive 

 layer itself. Had excitation been attended with change of 

 light into shade, we should have witnessed the spectacle of 

 a deep shadow, vanishing tow r ard the edges, and spreading 

 over the different layers of cells during displacement of 

 organs from vertical to horizontal ; the shadow would have 

 disappeared on the restoration of the organ to the vertical 

 position. 



Different shades of excitation in different layers are, 

 however, capable of discrimination by means of the insu- 

 lated electric probe, as it is pushed into the organ from 

 outside. In actual experiment the probe exhibited in- 

 creasing excitatory electric change during approach to the 

 perceptive layer, which reached its climax when the 

 probe came in contact with that layer. When it passed 

 beyond this point, the electric indication of excitation 



