EXERCISE 74 



In addition to the pressure resulting from the action of osmosis in the root, and in addition to the 

 apparent " pull " resulting from the transpiration of water from the leaf, liquids are said to rise in stems 

 because of the capillarity of the vessels. 



Problem. What is the relation between the diameter of a vessel and the height to 

 which liquids will rise in it without additional force being applied to them ? 



What to use. Glass tubes of various diameters ; vessel containing water that has 

 been colored with a few drops of red or blue ink. 



What to do. Place the glass tubes vertically in the liquids ; note the height to 

 which the liquid rises in each tube. Estimate the relative sizes of the tubes, in internal 

 diameter. 



Record. Make a diagram showing the approximate sizes of the tubes used and the heights to 

 which the liquid rose in each. Tell what relation you find between the diameter of a vessel and the 

 extent to which a fluid will be drawn up in it. 



Questions. 1. Would the vessels, or ducts, of a plant raise water as much as glass tubes, or more, 

 or less? Why? 



2. For what practical purposes is capillary attraction used ? 



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