1« OF THE ASSIMILATION OF CARBON. 



ments. The atmosphere must thus receive a volume of oxygen 

 for every volume of carbonic acid, the carbon of which has be- 

 come a constituent of the plant. 



This remarkable property of plants has been demonstrated in 

 the most certain manner, and it is in the power of every person 

 to convince himself of its existence. The leaves and other green 

 parts of a plant absorb carbonic acid, and emit an equal volume 

 of oxygen. They possess this property quite independently of 

 the plant ; for, if after being separated from the stem, they are 

 placed in water containing carbonic acid, and exposed in that 

 condition to the sun's light, the carbonic acid is, after a time, 

 found to have disappeared entirely from the water. If the ex- 

 periment is conducted under a glass receiver filled with water, 

 the oxygen emitted from the plant may be collected and examined. 

 When no more oxygen gas is evolved, it is a sign that all the 

 dissolved carbonic acid is decomposed ; but the operation recom- 

 mences if a new portion of it is added. 



Plants do not emit gas when placed in water either free from 

 carbonic acid, or containing an alkali that protects it from assi- 

 milation. 



These observations were first made by Priestley and Senne- 

 bier. The excellent experiments of De Saussure have further 

 shown, that plants increase in weight during the decomposition 

 of carbonic acid and separation of oxygen. This increase in 

 weight is greater than can be accounted for by the quantity of 

 carbon assimilated ; a fact which confirms the view, that the ele- 

 ments of water are assimilated at the same time. 



The life of plants is closely connected with that of animals, in 

 a most simple manner, and for a wise and sublime purpose. 



The presence of a rich and luxuriant vegetation may be con- 

 ceived without the concurrence of animal life, but the existence 

 of animals is undoubtedly dependent upon the life and develop- 

 ment of plants. 



Plants not only afford the means of nutrition for the growth 

 and continuance of animal organization, but they likewise furnish 

 that which is essential for the support of the important vital pro- 

 cess of respiration ; for, besides separating all noxious matters 

 from the atmosphere, they are an inexhaustible source of pure 



