292 RESEARCHES ON IRRITABILITY OF PLANTS 



shorter open end of a narrow u-tube filled with water. For 

 this purpose an indiarubber cork is taken, and a slit made 

 from circumference to centre. The petiole is then slipped 

 into the centre of the cork, which is gently forced on to the 

 short open end of the u-tube. The longer end of the u-tube 

 partly consists of indiarubber tubing. By raising or lower- 



FiG. 141. — U-tube support for leaflet, and the plant chamber. 



ing this longer limb of the u-tube the hydrostatic pressure 

 to which the specimen is being subjected can be varied ; 

 different chemical solutions can also be applied internally by 

 its means ; a stopcock allows the water to run out of the 

 u-tube, making way for the particular solution poured in 

 at the open end of the tube. 



The u-tube (fig. 141) is hinged on a rod which slides 

 up and down inside an upright tubular support. This 

 rod can also be rotated inside its support and clamped in 

 any desired position. Facilities are thus secured for three 



