56 



Elementary Plant Physiology. 



in a rubber stopper. Fix the stopper in one of the mouths of 

 a U-tube, or, if this is not at hand, use two short tubes connected 

 by a short section of rubber tubing. Fill the U-tube with water, 

 and support it in sunlight. The shoot will doubtless wilt and 

 assume a drooping position. Now pour enough mercury in the 



Fig. 34. — Effect of forcing water into a wilted stem, g^ level of mercury when 

 poured into U-tube, to which is fastened a flagging shoot ; w, water ; k^ stopper 

 supporting shoot. The continued action of the shoot lifts the mercury in the arm 

 underneath it. After Sachs. 



open end of the U-tube to make a column several centimeters 

 in height, and drive the water against the end of the stem, '\\'ith 

 a strong pressure. Unless the stem is wilted too badly it may 

 be restored by this method, which furnishes the depleted cells 

 with sufficient water to allow them to regain their normal tur- 

 gidity and consequent rigidity (Fig. 34). 



