loCalisatiok of geo-perCeptive layer 479 



theory of statoliths propouiKk'tl by Noll, Haberlandt and 

 Nemec. But for the clear understanding of the physiological 

 reaction which induces the orientating movement, it is neces- 

 sary to get hold, as it were, of a single or a group of 

 sensory cells in situ and in a condition of fullest vital 

 activity ; to detect and follow by some subtle means the 

 change induced in the perceptive organ and the irradiation 

 of excitation to neighbouring cells, through the entire 

 cycles of reaction, from the onset of geotropic stimulus 

 to its cessation. 



The idea of obtaining access to the unknown geo-percep- 

 tive cell in the interior of the organ for carrying out 

 various physiological tests would appear to be very extra- 

 vagant ; yet I could not altogether give up the thought that 

 the obscure problem of geotropic action might be attacked 

 with some chance of success, by means of an electric probe 

 which would explore the excitatory electric distribution in 

 the interior of the organ. But the experimental difficulties 

 which stood in the way were so great that for a long time 

 I gave up any serious attempt to pursue the subject. And 

 it is only when the present volume is going through the 

 press that the very first experiments undertaken proved so 

 highly successful that I am able to give a short account of 

 the more important results, which cast a flood of light on 

 the obscurities of geotropic phenomena. The new method 

 has opened out, moreover, a very extensive range of 

 investigation on the activities of cells in the interior of 

 an organ, and enabled me to localise the conducting 

 ' nerve ' which transmits excitation in plants. These and 

 other results will be given in the next volume. 



METHOD OF EXPLORATION BY THE ELECTRIC PROBE. 



The principle of the new method will be better under- 

 stood if I first explained the steps of reasoning by which 



