LEAVES 909 



from the pot. If the area of the leaves is then ascer- 

 tained, it is possible to know how much water is 

 evaporated per day. per square inch. It has been 

 estimated that a sunflower plant transpires about a 

 quart of water on a warm day. A tree transpires a 

 great quantity of water, in some cases as much as 175 

 gallons a day. The grass on an average city lot will 

 distribute to the air at least half a ton of water in twenty- 

 four hours. 



Disadvantages of transpiration. The disadvantages 

 to the plant of this great loss of water are very evident. 

 From personal observation, you know that many plants 

 die because of lack of water, which evaporates from 

 them more rapidly than they can replace it. This 

 excessive loss of water is the greatest danger to which 

 plants are exposed, and it renders necessary constant 

 provision for water in the soil where plants grow. 



Advantages to plant. There is a difference of opinion 

 as to the advantages of transpiration in plants. Recent 

 experiments indicate that this process of evaporation 

 cools the leaves and thus prevents them from being 

 overheated. Water passing out of the leaves makes it 

 possible for more water to enter at the roots. As a 

 result, there is a stream of water passing through 

 the plant constantly, entering through the roots and 

 going out through the leaves. This is known as the 

 transpiration current. Entering the roots with the 

 water a#e solutes, mineral substances in solution. These 

 solutes must pass from the roots to the leaves, a 



