SOIL NUTRIENTS 79 



crops introduces these bacteria into his field by the appli- 

 cation of soil taken from a field known to have them, or 

 possibly in some cases he introduces the bacteria by the use 

 of commercial cultures. Certain legume crops, as alfalfa, will 

 do poorly unless the bacteria are present. 



165. A simple experiment will demonstrate the growth 

 of plants in a nutrient solution, such as may exist in the 

 soil. Secure from the druggist the following chemicals and 

 make a solution of them, using the amounts here indicated: 



Potassium nitrate, KNO 3 2 grains 



Calcium phosphate, monobasic, CaH 4 (PO 4 )2 1 grain 



Or Calcium phosphate dibasic Ca 2 H 2 (PO 4 )2 1 grain 



Magnesium sulfate, MgSO 4 0.50 grain 



Ferric chloride, very slight trace. 



Water (distilled) .5 quarts 



Fill four or five tumblers with this solution and cover 

 the tumblers with paraffined paper. Germinate peas or seeds 

 of a similar plant, and when the roots are two inches long 

 punch holes in the paper and insert the roots through the 

 holes into the nutrient solution. Place the cultures in good 

 light and allow the seedlings to grow three or four weeks. 

 For comparison, grow some of the plants in distilled water 

 in place of the nutrient solution. 



166. Transpiration. We have found that the plant 

 takes nutrients from the soil in very dilute solutions. Much 

 more water is absorbed by the roots than is used in growth, 

 and this surplus water is given off from the leaves into the 

 atmosphere by the evaporation process known as trans- 

 piration (157). The transpiration takes place more abun- 

 dantly from the under surfaces of leaves in most plants, 

 and through the pores or stomates. It has been found that a 

 sunflower 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 150 gallons per day 



