DIRECTIONS FOR LABORATORY STUDY. 395 



water. (To accomplish this bend the shoot to be cut off so that 

 the place of the cut is submerged in a deep pan of water. Fit it 

 in tube without exposing cut surface at all to air.) Dip the lower 

 end of the capillary tube in water and allow apparatus to stand 

 until capillary tube fills with water. Remove the water for a 

 moment and allow a bubble I cm. long to enter ; time it as it 

 moves between a series of equidistant marks on capillary tube. 

 Try the rate under various conditions of light, temperature, and 

 moisture acting on shoot. 



14. To show the lifting power of evaporation. (^[207.) 



Cut off under water a shoot from a thrifty plant ; fasten it air- 

 tight in the end of a piece of glass tubing 30 cm. long, of appro- 

 priate diameter, by means of a piece of rubber tubing slipped 

 over the end of the stem, taking care not to expose the cut end to 

 air. Fill glass tube with water before fitting in plant ; erect the 

 whole with lower end of tube dipping in a cup of mercury. Set 

 in light and note height of mercury in 1-48 hours. 



15. To show loss of liquid water when absorption is great and 

 evaporation slow. 



Grow seedlings of wheat or oats until 5-10 cm. high ; then 

 cover with a glass bell for an hour or two. Where do drops of 

 water appear? Why? 



16. To show roughly the path of evaporation stream in woody 

 plants. (If 206.) 



A. From a leafy shoot of a woody plant remove a ring of bark 

 5 mm. wide. Protect the exposed surface against drying with 

 grafting wax. Observe whether the leaves wilt or not, and if 

 they wilt, the time required. 



B. With a knife or fine saw cut a little over half through the 

 stem of a plant of the same sort used in A ; 1 cm. above this cut 

 make a similar one on the opposite side. The two must be so 

 placed and of such a depth that all the tissues are severed. Sup- 

 port the branch or stiffen it against breaking by bandaging it with 

 strips of wood. Make same observations as in A. Examine the 

 pith. Is it alive? Does it contain water ? In what tissues, there- 

 fore, do you infer water travels to leaves? 



17. To show restoration and maintenance of an interrupted evap- 

 oration stream. 



Fit a well wilted shoot into the short arm of an unequal U-tube 

 filled with water to the level of the short end. Allow it to stand 

 for half an hour. Does the shoot recover? If not, pour mercury 



