CH.IIl] 



ROOT PRESSURE. 



69 



stump is attached by rubber tubing to a potometer tube^ 

 filled with a solution of nigrosin in water ; to one arm of 

 the potometer a vertical glass tube, a few mm. in diameter 

 and several feet in length, is attached ; the other arm of 

 the potometer is closed with a cork. The nigrosin seems 

 to have no bad effect on the plant and makes the rising 

 column of fluid easily visible. If the tube is supported 

 against a wall it can be elongated by fresh lengths of glass 

 tubing and thus a column of 8 or 10 feet can easily be 

 shown. 



(89 A) Root pressure. 



The classical method of observing root pressure is that 

 described and figured by Sachs in his Physiologie V4g6tale 

 (Fr. Trans.), p. 223, of which the following (Fig. 12) 



Fig. 12. Exp. 89 A. 



is a modification. A T tube (T) having one arm B bent 

 1 The arrangement is similar to that figured in Sachs' VorUsungen, 

 p. 328, fig. 211. 



