Waterivays in Plants 



59 



the cut end and run down the stem. Pressure from below 

 forces it up.^ 



In order to see how long this continues, we may try another 

 experiment. It will require a vigorous young plant such as a 

 Castor Oil, Felargoiiiiun, or Grape Vine, a piece of glass tubing 

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



Ex. 20. 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 btem 

 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 

 constantly rise ? 



Ex. 21. What becomes of the 

 water? 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 e\'apora- 

 tion, or thrust the cut end through a 

 stopper and seal with \vax. 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 plice. 



Ex. 22. Soak strips of paper in cobalt chloride. Dry thoroughly', and 

 notice how they change from red to blue as they dry. Dry the inside of 

 the jar containing the plant. After remaining in the bell-jar ior a while 

 the paper changes back to red, This also shows that vapour is passing 

 from the leaves. 



Fig. 67. — Apparatus to demon- 

 strate root-pressure. The cut 

 stem is fastened to a glass tube 

 by means of rubber tubing. The 

 tube leads by an arm into the 

 jar (J). Both are filled with water 

 with mercury in the bottom of 

 the jar. As the cells in the root 

 force the water into the tube the 

 mercury is forced up into the 

 small tube, /. 



^ This pressure accounts only in part for the upward ascent, which 

 is not fully understood. Evaporation from the leaf surface is doubtless 

 connected with the lifting of water. 



