CHAPTER V 

 ABSORPTION OF WATER 



42. Importance of Water. Everyone knows that plants 

 must have a suitable amount of water in order to live and 

 keep healthy. Deprived of water they wilt, and finally 

 die. If they are given too much water they also suffer. 

 The water serves many purposes. In the first place, it 

 is needed to keep the protoplasm sufficiently moist. Pro- 

 toplasm may keep alive though very dry, as in the case 

 of dry seeds, but in order to be most active it must have 

 enough water to keep it in a semi-fluid condition. In 

 the second place, were it not for water, no food materials 

 could reach the protoplasts, for there are, in general, no 

 openings in the cell-walls large enough for solid matter to 

 pass through. Therefore, all substances must reach the 

 protoplasts in aqueous solution. Again, water is neces- 

 sary in the transportation of materials from one part of 

 a plant to another; and finally, it is necessary in order to 

 keep plants from wilting, for no plant can live if it is 

 permanently wilted. 



43. Relative Water Requirement. The amount of 

 water required by various kinds of plants in order to 

 reach maturity and produce seeds varies greatly. It 

 depends in part upon the weather conditions (e.g., sun- 

 shine, wind, humidity, and other factors), in part upon 

 food supply, and in part upon the species or variety of 

 plant. Some species are so constructed that they con- 



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