Conditions and Principles of Absorption 79 



A demonstration of the quantity of liquid pro- 

 duced, and of the existence of root pressure, may 

 be made by comparatively simple methods. The 

 quantity is readily determined by cutting off the 

 plant an inch or two above the surface of the 

 ground and connecting the stump by rubber and 

 glass tubing with a measuring glass protected 

 against evaporation. For the proper demon- 

 stration of pressure a suitable manometer is re- 

 quired (Fig. 21). 



LABORATORY WORK 



Imbibition; swelling of wood. - -Use small blocks of 

 oak, basswood, and pine, practically cuboidal in form, 

 preferably cut so that tangential, radial, and longi- 

 tudinal axes are represented. Mark opposite points 

 of each axis with a pencil and measure carefully with 

 the calipers provided. Then soak the 

 blocks in distilled water for from five 

 to ten days, changing water each day ; 

 after which, remeasure each axis and 

 compute the percentage of change. 



Heat of imbibition. - - Reduce 100 

 grams of common starch to a uniform 

 powder, dry in an 

 oven at about 105 C., 

 and at the same time, 

 for a control experi- 

 ment, dry 100 grams 

 of quartz flour or 

 graphite. Cool both 

 powders to room tem- 

 perature in a desic- 

 cator, and pour each ^ 



-~ riG. 21. Ganong's manometer. [After the 



into a Dewar flask or Bausch and Lomb Optical Company.] 



