THE RECORD OF GROWTH-RESPONSE 423 



variation, which produces an expansion of the responding 

 zone of growth. The growth-response is thus the indirect 

 effect of stimulation. 



The rhythmic activity of internal tissue supplies its motive 

 power to the zone of growth. This activity, depending on 

 the tonic condition of the plant, constitutes the ' inner 

 stimuli ' to which growth is to be ascribed. 



