ORIGIN AND FORMATION OF ORGANIC MATTER IN PLANTS. 



P. P. Deiierain, 

 Member of the Institute of France. 



By the ordinary method of sand culture, in which the plant is grown 

 in sand free from organic matter, it may be demonstrated that the plant 

 accumulates considerable quantities of carbon and nitrogen during its 

 growth. This carbon and nitrogen with the elements of water form the 

 organic constituents of the plants, which with a small quantity of min- 

 eral ingredients make up the roots, stem, and leaves and give the seed 

 its valuable nutritive qualities. Since the soil did not contain either 

 carbon or nitrogen, the plant must have drawn these two elements from 

 the air. It is the purpose of this article to explain the nature of this 

 fixation of the carbon and nitrogen of the air. 



ORIGIN OF THE CARBON OF PLANTS. 



The classic experiments of Priestley, in 1771, established the fact 

 that plants exhale oxygen. Later researches made by Ingenuous and 

 by Tennebier explained the decomposition of the carbon dioxid of the 

 air and the evolution of oxygen by the leaves under the influence of 

 light. The experimental demonstration of this decomposition is easily 

 made by the method of Cloez and Gratiolet as follows : 



Introduce in a liter bottle of white glass 200 cc. of water saturated 

 with carbon dioxid. Fill the bottle with ordinary water and immerse 

 in the liquid branches of such marsh plants as Elodea canadensis, 

 Ceratophylhtm submcrsum, or Potamogeton crispus. Close the bottle with 

 a rubber stopper provided with a tube for drawing off the gas evolved 

 and place in the sunlight. After a few hours a considerable amount 

 of gas is obtained which is rich in oxygen. The green plants therefore 

 draw their carbon from the carbon dioxid and it is important to under- 

 stand the process by which this is done. 



PENETRATION OF THE CARBON DIOXID INTO THE LEAVES. 



The earth's atmosphere contains only 3 parts of carbon dioxid in 

 10,000 of air. It is evident, therefore, that in order that plants may 

 obtain the carbon which they require from a medium eo poorly supplied 

 with it rapidity of absorption by the tissues must compensate for the 

 scarcity of the element in the air. 



In the first place the absorption of carbon dioxid is favored by the 

 form of the leaves, which is such that they offer, as compared with their 

 weight, an enormous absorbing surface. In a tree the leaves are at the 



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