62 



CORN 



turgidity of the entire plant. When every cell is full of water these 

 guard cells dilate the stomata and evaporation is increased. In con- 

 trast, if the roots fail to furnish a sufficient supply of moisture, the 

 wilting of the leaves relaxes the guard cells and the opening of the 

 stomata closes and transpiration is diminished. The curling of corn 

 leaves in July indicates that the roots are securing insufficient mois- 

 ture. When the atmosphere is clear, dry and hot, and the wind is 

 blowing briskly, transpiration is increased even though the stomata 

 are practically closed. Coolness and dafnpness of the air tends to 

 reduce the passage of moisture from the stomata. 



*The following was found to be true regarding the amount in tons 

 of water per ton of dry matter lost by transpiration through the plant 

 and evaporation of the soil : 



Dent corn used 309.8 tons of water per ton of dry matter. 



(4) Aids in the physical change of plant food. 



The nitrates, the form in which all nitrogen enters the plant, are 

 soluble in water. This compound is drawn in with the soil moisture 

 by the root hairs. Other soil constituents are also soluble in water. 

 "The weight of evidence supports the conclusion that water is capable 

 of dissolving from the soil all the substances that it contains which 

 serve as the food of plants."** A few analists assert that phosphoric 

 acid is not soluble in water alone. Yet experiments have proved its 

 presence in water solutions of ten days standing. It must be kept in 

 mind, however, that only weak solutions of plant food are readily 

 absorbed and assimilated. Care should be taken then that manure 

 containing a large amount of available and soluble elements is not 

 applied heavily to the corn crop. In.ca.=e of excess, the plant is 

 injured. The presence of carbon dioxide in water renders it more 

 effective in dissolving the food materials in the soil. 



(5) Water enters into the chemical processes . within the plant. 

 In all probability, carbonic acid and water are decomposed at the 



same time by the action of the sun's rays through the chlorophyll, in 



*"The Soil," King, Page 155. 



**John8on'8 "How Plants Feed," Page 316. 



"^'Warrington'? "Chemistry of the Farm," Page 6. 



