SOIL MOISTURE 45 



poses which soil moisture serves: (1) dissolving plant foods; 

 (2) transferring plant foods; (3) supplying plant food in itself; 

 (4) regulating soil temperature and plant temperature. 



Plant Food Solvent. The mineral elements are dissolved out of 

 the soil by water charged with carbon dioxide and humic acid 

 and are made available for the use of the plant. 



The Vehicle of Plant Foods. The passage of liquids through 

 a membrane is called osmosis, and it plays an important part in 

 plant structure and plant growth. ' The soil water containing the 

 soluble food elements is taken up through the membranes covering 

 the roots of the plant and passes through the young wood of the 

 plant upward to the leaves which manufacture the starch and sugar. 

 These leaf-formed foods are then carried downward through the 

 bark to all parts of the plant. 



Water as a Source of Plant Food. It is an easy matter to make 

 many plants grow in water provided the water contains some nu- 

 trient salts, or the stored food in the cotyledons of the seedling is 

 available. Hyacinths and narcissus bulbs may be made to bloom in 

 water cultures. Beans, corn, wheat, or other grains, after sprouting, 

 may be supported so that their roots are in water, and so long as the 

 decaying seed or the water culture furnishes food, the plant grows. 

 Water enters into combination with other compounds in the plant 

 tissues, but pure water alone will not produce growth in plants. 



Water as a Temperature Regulator. Moisture and Soil Tempera- 

 ture. The water from spring and summer rains is usually warmer 

 than the soil and tends to raise the temperature, while that from 

 -inter rains is cooler than the soil and tends to lower the tempera- 

 iure. A dry soil is always warmer than a wet one. Many of the 

 heat waves which fall on wet land are used up in evaporating its 

 surplus water, while the heat waves on a dry soil are used to raise 

 its temperature. The question of soil temperature is an important 

 one to the farmer and should be studied closely. The lowest tem- 

 peratures at which growth may be started, according to Ebermayer, 

 is from 45 to 48, but the best results are obtained at a tempera- 

 ture of 68 to 70. The germination of wheat, rye, oats, and flax 

 proceeds most rapidly at 77 to 87 F. and corn and pumpkins 

 germinate best at 92 to 101 F. Corn that will germinate in 

 three days at a temperature of 65.3 F. requires eleven days when 





