go chap. vi. relation of turgor and tension 



Effect of External Tension 



Excessive tension is usually found to retard the rate 

 of growth. This is one of the defects of the ordinary auxano- 

 meter, in which the recording lever exerts a considerable 

 pull on the plant. 



Experiment 32. — The effect of gradual increase of tension 

 on growth is observed as follows. The recording levers of the 

 Crescograph are at first so balanced that very little tension 

 is exerted on the plant, the record now giving the normal 

 rate. The tension is then graduahy increased from i grm. 

 to 10 grm. When the growing organ is subjected to an 

 increase of tension, the immediate effect is an excitatory 

 contraction. But this transient effect disappears in a short 

 time, after which it is easy to observe the permanent effect 

 of tension on the rate of growth. 



Table VI. — Effect of Tension on Growth (Crinum). 



The results given in the table above were obtained 

 with Crinum ; they show that the growth-rate increases 

 with tension till a limit is reached, after which there is 

 retardation. 



Summary 



Increase of turgor due to rise of sap after irrigation 

 enhances the rate of growth. Enhanced rate of the ascent 

 caused by irrigation with warm water induces a further 

 augmentation of the rate of growth. 



The length of the latent period preceding the enhance- 

 nient of growth depends on the distance of the growing 



