CHAPTER X 

 WATER AND AGRICULTURE 



The Importance of Water to Plants. You know 

 how important water is to plants and also that water has 

 great effect in determining where men live. This is due to 

 the need of it for agriculture (food-production) quite as 

 much as to the need of it for direct use by man, and in con- 

 nection with transportation. Good crops depend upon 

 water, soil, and climate. Soil and climate suitable for agri- 

 culture are much more wide-spread than suitable water- 

 supply. Hence water-supply is the chief factor in modern 

 times in determining the location of farms. Until quite 

 recently the availability of a market for the crops was quite 

 as important a factor, but the modern development of trans- 

 portation has very largely solved this problem. 



To insure good crops of hay and grain, a water-supply 

 equivalent to at least ten inches of rainfall a year is needed. 

 Also this supply must be distributed throughout the 

 growing season of the plants; it will not do if it all comes 

 at once in heavy rains followed by long periods of drought. 



It is easy to demonstrate that water evaporates from 

 the leaves of plants. Place a bell-jar over a potted gera- 

 nium, covering pot and soil with sheet rubber; or a tum- 

 bler over a single leaf whose end is in covered water. 

 Droplets or a film of moisture will soon collect on the glass. 

 This is evidently a result of plant-evaporation, a process 

 which is technically called transpiration. 

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