PLANT FOOD 213 



EXPERIMENT FOR THE TEACHER 



See Farmers' Bulletin No. 408:37. Air Necessary for 

 Plants. 



If the botanical side is to be emphasized in the course, this 

 bulletin may be used to great advantage as a source of infor- 

 mation concerning experiments. 



Experiment 74. Air Necessary for Roots.* 



Apparatus : Two tumblers, or beakers, 125 c.c. 



Materials : Geranium cuttings, sweet oil. 



a. Boil some water, to drive out the air, cool it, and then fill 

 the two glasses three fourths full. Put a cutting of geranium 

 in each, but cover the surface of the water in one glass with a 

 thin layer of sweet oil. Observe the growth of roots. 



Soil which is too wet produces the same result. 



152. PLANT FOOD I 



The principal plant foods are nitrogen, phosphoric acid, 

 potash, and substances called amendments, which tend to set 

 free plant food already in the soil. Fertilizers contain dif- 

 ferent compounds of the above substances. 



When we add a fertilizer to the soil, we say that we are im- 

 proving the land. In reality, we are not interested in whether 

 the land is good or bad, but we are careful to see that the com- 

 ing plants will have food enough; just as we do not throw 

 food out into the chicken yard to improve the chicken yard, 

 but to feed the chickens. There may be a large amount of 

 plant food already in the ground, but unless it is in a condi- 

 tion in which it can be absorbed by the plants, it might as 



* From Farmers' Bulletin No. 408. 



