Waterways m Plants 



57 



castor oil, pelargonium, or grape vine, a piece of glass tubing 

 as large as the stem, also some string and a stake of wood. 



Cut the stem an inch or two from the soil. Slip one end 

 of the rubber tubing over the glass and the other over the cut 

 stem which was left in the 

 soil. Place a little water in 

 the tube to prevent the stem 

 from drying and tie the glass 

 firmly to the stake. Be sure 

 that the rubber makes a tight 

 joint. It may be tied at each 

 end. The water will rise in 

 the tube. At the close of the 

 day mark the height at which 

 the water stands. Notice how 

 much has passed during the 

 night. Mark the height at 

 each hour of the day. Are 

 the marks the same distance 

 apart? Does the water con- 

 stantly rise ? 



What becomes of the 

 water P Place the upper 

 part of the plant cut off in 

 the last experiment in a 

 slender jar of water. Pour 

 a layer of oil over the top to 

 prevent evaporation, or thrust 

 the cut end through a stopper 

 and seal with wax. Cover 

 the whole with a bell-jar or 

 a fruit-jar. See that the glass is quite dry before covering. 

 In a short time the jar will be lined with a thin mist, which will 

 collect in drops of water. 



Water passes from the leaves and stem of a plant 

 in the form of vapour. As the leaves give off vapour more 

 water is drawn up to take its place. Thick sap in tiny cells of 

 the leaf draws it up. 



Fig. 67. — Apparatus for measuring the root- 

 pressure. A manometer, a, b, c, is fixed 

 into the upper part of the plant / growing 

 in a pot, the top having been cut off. The 

 difference in the height of the mercury in 

 the two arms b andc indicates the intensity 

 of the pressure by which the water sucked 

 up by the roots is forced out at the cut 

 section. (From Thome and Bennett's 

 " Structural and Physiological Botany.") 



