86 



CHAP. IX. GROWTH IN SUBTONIC PLANTS 



Table X. — Acceleration of Growth in Subtonic Specimens 

 BY Electric and Photic Stimulation. 



The effect of direct stimulation upon growth Las thus 

 been shown to be modified by the tonic condition of the 

 plant, there being an enhancement of the rate when the 

 plant is in a state of subtonicity. Is there any other con- 

 dition under which stim.ulus enhances the rate of growth ? 

 I take up the question in a future chapter. 



Summary 



The sign of the response of an organ is dependent on its 

 tonic condition. 



When the pulvinus of Mimosa is in a subtonic condition, 

 the response to stimulation is positive, that is expansion 

 and erectile movement, instead of the negative response of 

 contraction and resulting fall of the leaf. 



As the result of continuous stimiulation the tonicity is 

 raised to a condition of par, the abnormal positive response 

 being converted into the normal negative. 



The effect of stimulation on growth is modified in a 

 parallel manner, according to the tonic condition of the 

 organ. 



When the organ is in a subtonic condition, it responds 

 to stimulation by an enhancement of its rate of growth. 



In extreme cases, growth in a state of standstill becomes 

 revived under stimulation. 



Continuous stimulation of a subtonic organ by light or 

 by electric current raises the tonic condition of the growing 

 tissue, the response of acceleration becoming transformed 

 into one of normal retardation. 



