CHAPTER FIVE 



THE WATER RELATIONS OF LEAVES 



DURING a prolonged drought in Illinois, in 1914, oats in some 

 places failed to attain a height of more than 4 inches and 

 produced practically no grain, and corn which should have 

 averaged 10 feet in height reached only 5 feet in many fields, 

 and yielded only half the normal amount of grain. In the 

 four great corn-growing states there must be 3 inches of 

 rainfall in July for the best yield of corn ; and if the rainfall 

 during July is 2-J inches instead of 3, it is estimated that at 

 normal prices there is an average loss of $5 an acre, or a total 

 loss of $150,000,000. Those who cultivate plants know from 

 experience the importance of a sufficient water supply in the 

 production of crops, and the reason why the water supply is 

 important will be apparent when we understand the uses 

 made of water by the plant. 



Why water is necessary to a plant. The active protoplasm 

 of all plant cells is in a semiliquid condition. More than 

 90 per cent of its weight is made up of water, and in consist- 

 ency it closely resembles white of egg. The several parts of 

 the protoplasm the cytoplasm, the nucleus, and the plas- 

 tids differ somewhat in their water content, but all of 

 them must be nearly saturated with water to carry on the 

 life processes. When the amount of water in the cell 

 falls much below this point, the protoplasm becomes rigid 

 and its processes are retarded. In many plants the pro- 

 toplasm may even die if the water content is greatly 

 reduced. Water is necessary for the life of the protoplasm of 

 plant cells. 



Water is one of the materials used in the production- of 

 carbohydrate. Without it the process of photosynthesis, 



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