EXERCISE 49 

 HOW KAPIDLY DOES WATEK EVAPORATE FHOM A PLANT? 



Materials. A potted plant ; a sheet of thin rubber (dentist's rubber) large enough to inclose the 

 pot in which the plant grows ; balances. 



Directions. The plant should be well watered and then wrapped in such manner that water 

 cannot evaporate from the soil or pot. To do this, wrap the pot in a sheet of thin rubber and 

 tie so as to hold the rubber closely around the stem. This can be done more securely if the plant 

 selected has but a single stem. 



Weigh the pot and the plant after wrapping. Set it in a light place and weigh again from time 

 to time hourly, if possible. Record your weights in the table below. 



What does a loss of weight indicate ? Can you account for any changes in rate of evaporation ? 

 What are the reasons for wrapping the pot with rubber ? 



DATE 



TIME 



Loss PER HOUR 



Additional problems. Water sometimes evaporates more rapidly from a vegetated area than from a 

 similar area of free water. Explain this fact. 



Why must house plants be watered more abundantly on dry, hot days than on cloudy days ? 



Determine the area of the leaves used in the above exercise and calculate the daily evaporation per 

 square centimeter (evaporation occurs usually from the lower surface only). 



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