faces of leaves, and through the pores orstomates. It has been 

 found that a sun-flower plant of the height of a man during an 

 active period of growth gives off more than a quart of water per 

 day. A large oak tree may transpire one hundred and fifty 

 gallons per day during the summer. For every ounce of dry 

 matter produced, it is estimated that from fifteen to twenty-five 

 pounds of water must pass through the plant. 



15. Whe7i the roots fail to supply to the plant sufficient ivater to 

 cqtialize that ti'anspired by the leaves, the phuit wilts. — Transpiration 

 from the leaves and delicate shoots is increased by all of the 

 conditions which would increase evaporation ; such as higher 

 temperature, dry air, wind, etc. 



The stomates are so constructed that they open and close with 

 the varying conditions of the atmosphere, attempting to regulate 

 transpiration. However, during periods of drought, or of very 

 hot weather, and especially during a hot wind, the closing of 

 these stomates cannot sufhcientl}^ prevent evaporation. The 

 roots may be very active, and yet fail to absorb sufficient mois- 

 ture to equalize that given off by the leaves. As a consequence 

 of this, the plant wilts. Any injury to the roots, or even chill- 

 ing them, may cause the plant to wilt. ^ On a hot, dr}' day note 

 how the leaves of corn "roll" towards afternoon. Early the 

 following morning note how fresh and vigorous the same leaves 

 appear. 



The wilting of a plant is due to the loss of water from the 

 cells. The cell walls are soft, and collapse. A grain bag will 

 not stand alone, but it will stand when filled with wheat. In 

 the wood}' parts of the plant, the cell walls may be stiff enough 

 to support themselves, even though the cell is empty. 



