Exchange and Movements of Gases and Liquids. 71 



tube with boiled water. Support in an upright position, with 

 the lower end of the tube immersed in mercury to the zero 

 point, or to the lowest division of the calibrated portion. If 

 the leafy shoot withdraws water from the tube, mercury 

 drawn up will replace it. Transpiration thus exercises an 

 indirect lifting power. The living cells in the leaves give 

 off watery vapor into the intercellular spaces, and withdraw 

 water from the nearest cells to replace the loss. These in turn 

 act in the same manner until those nearest the woody cells are 



Fig. 50. — Method of cutting brancli under water. After Oels. 



replenished from them, and thus communicate the movement 

 throughout the entire branch. The branch may be joined to 

 the tube by a short section of rubber tubing. In this instance 

 the joints should be wrapped with wire twisted into position. 



65. Estimation of amount of water transpired. — 

 Secure a balance with a capacity of 5 kilograms, and a plant 

 growing in a four or five inch pot, and which has a large leaf 

 surface. Set the pot in a small glass jar, and tie a sheet of 

 rubber around the top of the jar and the base of the stem by 

 means of a cord, taking precautions not to injure the plant. 



