The Erectne^s of Plants. 



93 



Such a group of cells is called a me)-istem. Each cell in this 

 group contains, according to tliis theory, protein particles which 

 carry electro-positive charges because the rest of the cytoplasm in 

 the root cells is relatively acidic. When the root is placed 

 horizontally the particles, Avhich are more or less uniformly 

 distributed in the outer zones of cytoplasm, start to cream 

 upwards. As these particles move upwards, and because they 

 are positively charged, they develop a potential difference between 

 tlie upper and the under sides of each cell. The greater number 

 of positive charges proceed upwards, therefore the current, which 

 is developed as a result of the potential difference, passes 

 downwards. 



Now each cell of the meristem is connected to its neighbours 

 by very fine protoplasmic threads, and it is quite probable that 

 the cells are by this means connected electrically in parallel and 

 in series to form a battery. This battery, when the root is 

 placed horizontally, gives quite a recognisable electric current, 

 which passes downwards and along the cortex of the under side 

 of the root (fig. 1). Then it passes around the root and returns 























A 



i 



Trtpr^f— 



-75^ 





|b 









"TT" 























^^ 





d^ 







|l 



!r^^ 





-f 

























¥ 







4 





in 



— 









1 























^ 



































IKj^ 



































^ 







\ 



























"t 







\ 



C\f 



















-J 





— 





J,-! 



4 



L ., 7l\ 

















' 



— 







— 



— 







r'TTT':.^ 



MOTOR REGIOn 



PERCEPTIVE @ REGIOn 



Fig. 1 — Diagram of root apex to illustrate the Hydrion. Differentiation Theory of 

 geotropism. The "creaming" is indicated in the apical meristem 

 (perceptive region). The arrows indicate the path of the "action cirrrent." 

 A.B. Two electrodes ixsed in measuring the changes in conductivity under 

 geotropic stimulation. 



along the upper side. The tissue has a very high electrical 

 resistance ; for this reason and because there are numerous 

 possibilities of leakage iu the circuit, the current is stronger in 



