INTERNAL HYDROSTATIC PRESSURE 



59 



Effect of Artificial Increase of Internal 

 Hydrostatic Pressure 



Experiment 31. — The plant was mounted watertight 

 in the short hmb of a U-tube, and subjected to increased 

 hydrostatic pressure by increasing the height of water in 

 the longer limb. The records were taken only when the 

 rate of growth under the changed condition had become 

 uniform, which occurs, generally speaking, in the course 

 of about 5 minutes. Increasing internal hydrostatic pres- 

 sure was found to increase the rate of growth up to a 

 critical point, after which there was a decline. It is inter- 

 esting to note that the motility of the pulvinus of Mimosa 

 also undergoes a marked diminution under the condition 

 of excessive turgor. 



The critical pressure beyond which growth exhibits 

 retardation is different in diverse species of plants. In 

 Kysoor it is about 4 cm. pressure of water ; in Crinum Lily 

 it is as high as 30 cm. The curve which gives the relation 

 between internal pressure and rate of growth is S-shaped. 

 It rises slowly in the first part, and more quickly in the 

 second ; it then becomes horizontal and finally reversed, 

 indicative of retardation. 



The following tabular statement gives the effect of 

 increased internal hydrostatic pressure on the rate of growth 

 in two different specimens of Kysoor. 



Table V. — Effect of Increased Hydrostatic Pressure 



ON Growth. 



