PLANT-FOOD AND AGRICULTURE. 223 



could figure as absolutely close as this illustration ; but if we have 

 clinched the idea, our purpose is accomplished. 



We now shall offer a few propositions concerning plant-food, 

 agriculturally considered, which have been conclusively proved, 

 and may be accepted as facts : 



1st. The soil contains plant-food. 



2d. The plant removes this plant-food from the soil. 



3d. Analyses of plants will show the character and quantity of 

 the plant-food removed from the land. 



4th. A supply of the elements removed by the plants to the 

 soil, in such a way that they can be appropriated by the plants, 

 will produce the plant-growth, under proper conditions. 



6th. Plants remove varying quantities of plant-food from the 

 soil, according to their species, their manner of growth, and the 

 proportions and quantities of plant-food present in the soil. 



6th. The constituents of plants furuislied from the atmosphere 

 being beyond our control, in studying plant-growth and food- 

 supply, we can limit ourselves to the earth alone, and study the 

 air-supply only as modified by our control over the elements sup- 

 plied to our land. 



7th. The soil contains the elements of plant-growth in varying 

 proportions and conditions; some elements far in excess of the 

 needs of our plant, other elements in quantities sufficient only to 

 support a scant growth. 



8th. The plant-food in the land must, to be of service to the 

 crop, be in a soluble state, or in a state capable of being taken up 

 by the rootlets of our plants. 



9th. When the elements of plant-food, in the form of chemicals or 

 dung, are added to our soil, there is a cliemical action taking place 

 between them and the soil constituents, in the presence of moisture. 



10th. The soil has the power of decomposing most of the chem- 

 icals which are applied, and has a retaining power on their com- 

 pounds, varying with the character of the element. 



11th. As a rule, phosphoric acid is firmly held by the soil, and 

 is not subject to loss through drainage, and has a limited diff'usi- 

 bility; potash is strongly retained, but has a greater diff'usibility; 

 nitrogen, in its various forms, is less strongly retained, and has a 

 ready diff'usibility. 



12th. In proportion to the presence of, and diffusion of these 

 fertile elements in our soil, other conditions being favorable, will 

 be the amount of our crop. 



