332 



CHAP. XXX. THE GEO-PERCEPTIVE LAYER 



of the galvanometer which decHnes and practically dis- 

 appears in the course of about 5 minutes. The geotropic 

 irritability is fully restored in the course of about 10 minutes, 

 after which a record of the geotropic response may be 

 taken. 



Experiment 180. Geo-electric response at different 

 depths. — I give below the photographic records of the 



Fig. 198. Intensity of geo-electric response at different depths 



in the petiole of Tropaeolum. 



Note the maximum excitation at a depth of 0-20 mm. 



response to the stimulus of gravity at different depths as 

 the probe was thrust in from outside by successive steps of 

 0-05 mm. (fig. 198). It will be seen that the geo-electric 

 response underwent a continuous increase till the maximum 

 excitation occurred at a depth of 0-20 mm. A rapid 

 decline occurred beyond this point, and the response dis- 

 appeared at a depth of 0-50 mm. The following table 

 gives the quantitative results of the experiment : 



