LOCALISATION OF GEO-PERCEPTIVE LAYER 499 



positivity of the lower layer in the ratio of about 

 2 : 1. But ill 11 depressed condition of the tissue, the 

 excitatory reaction is the first to disappear and the positive 

 reaction persists, though with diminished intensity. 



The geo-electrie distribution in vigorous specimens seems 

 to indicate that under the stimulus of gravity a marked 

 excitatory reaction (contraction) takes place in the layer 

 of cells contiguous to the upper geo-perceptive layer, and 

 a less niarked positive reaction (expansion) occurs in layers 

 contiguous to the lower perceptive layer. 



It is remarkable that physiological reaction of opposite 

 kinds should occur on the upper and lower sides of an 

 organ under the identical stimulus of gravity. The 

 difference of reaction may conceivably be connected with 

 the fact that the vertical lines of gravity enter by the 

 upper, and leave bj- the lower side of the organ. The 

 statolithic particles rest on the inner tangential walls of 

 the perceptive cells of the upper layer, and on the outer 

 tangential walls of the lower layer. Similar difference of 

 physiological reactions of a polar character are also known 

 in responses of plants under the action of an identical 

 electric current ; here with different ionic distributions, 

 contraction takes place at the kathode, and expansion at 

 the anode. 



The geo-electric reactions that have been described were 

 obtained under unfavourable conditions of climate and of 

 temperature. But under better conditions the reaction 

 becomes very greatly enhanced, as would appear from 

 the following account of results which I obtained 

 on two separate occasions in the beginning of August. 

 The season had not become quite as unfavourable as 

 towards the end of the month, but the prevailing sultry 

 weather had caused great depression of the geo-electric 



