ZU THE PLANT. 



The combustible constituents are derived from car- 

 bonic acid, ammonia, sulphuric acid, and water. 



By the vital process of vegetation, the body of the 

 plant is formed from these materials, which are there- 

 fore called the food of plants. All the materials con- 

 stituting 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 for- 

 mer, 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 

 atmosphere, and are, from their nature, in continual 

 motion. The fixed elements are, in the case of land- 

 plants, constituents of the soil, and cannot of themselves 

 leave the spot in which they are found. The cosmic 

 conditions of vegetable life are heat and sunlight. 



By the cooperation of the cosmic and the chemical 

 conditions, 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 in- 

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

 elements are nitrogenous substances, similar in compo- 

 sition to. the casein of milk or the albumen of the blood ; 

 and also starch, fat, gum, or sugar, with a certain quan- 

 tity of earthy phosphates and alkaline salts. The fari- 

 naceous body, or so-called albumen of the seed of corn, 

 as also the constituents 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 glass plate furnished with fine perfora- 

 tions, through which the roots may reach the water, 

 the grain will go. on growing for several weeks without 

 receiving any incombustible element of food or any 

 constituent of the soil. After three or four weeks the 

 apex of the first leaf is seen to turn yellow ; and upon 

 examining the seed, nothing but an empty skin is found, 

 for the starch has disappeared together with the cellu- 

 lose (Mitscherlich). However, the plant does not die 

 away, but new leaves are produced, often also a feeble 



