2 THE PLANT. 



Plants contain combustible and incombustible consti- 

 tuents. Of the latter, wliicli compose the ash left by all 

 parts of a plant on combustion, the most essential ele- 

 ments are — phosphoric acid, sulphuric acid, silicic acid, 

 potash, soda, lime, magnesia, iron, and chloride of sodium. 



The combustible constituents are derived from carbonic 

 acid, ammonia, suljjhuric acid, and water. 



By the vital process of vegetation, the body of the 

 plant is formed from these materials, which are therefore 

 called the food of plants. All the materials constituting 

 the food of our cultivated plants belong to the mineral 

 kingdom. The gaseous elements are absorbed by the 

 leaves, the fixed elements by the roots ; the former, 

 however, being often constituents of the soil also, may 

 reach the plant by the roots, as well as by the leaves. 



The gaseous elements form component parts of the at- 

 mosphere, and are, from their nature, in continual motion. 

 The fixed elements are, in the case of land-plants, consti- 

 tuents of the soil, and cannot of themselves leave the spot 

 in which they are found. The cosmic conditions of vege- 

 table hfe are heat and sunlight. 



By the cooperation of the cosmic and the chemical con- 

 ditions, the perfect plant is developed from the germ or 

 seed. The seed contains, within its own substance, the 

 elements required to form the organs which are intended 

 to take up food from the air and the soil. These elements 

 are nitrogenous substances, similar in composition to the 

 casein of milk or the albumen of the blood ; and also 

 starch, fat, gum, or sugar, with a certain quantity of earthy 

 phosphates and alkaline salts. The farinaceous body, or 

 so-called albumen, of the seed of corn, as also the consti- 

 tuents of the cotyledons in leguminous plants, become the 

 roots and leaves of the nascent plant. If corn-seeds are 

 set to germinate in water, and allowed to grow upon a 



