NOTE ON RESPIRATION 



A few additional facts are here given to supplement those stated in 

 Sect. 133.1 



Respiration can only be carried on by living protoplasts. 



It results in the breaking down of nitrogenous and non-nitrogenous sub- 

 stances in the cell contents. 



It may be due to the action of enzymes upon the oxidizable contents of 

 the respiring cells. 



It is likely that the oxidizable compounds destroyed in respiration are 

 broken down by the action of hydroxyl (OH) upon their molecules. This 

 hydroxyl is derived from the water present. 



Many of the lower plants, especially fungi, regularly perform what is 

 known as anaerobic or intramolecular respiration, in which the breaking down 

 of molecules of their tissues and release of energy is carried on without 

 access of any free oxygen. Some portions of the higher plants, e.g. seeds, 

 often manifest anaerobic respiration. This is readily shown by soaked peas. 



In the ordinary respiration of the higher plants free oxygen, taken in 

 from the atmosphere, serves to reconstruct the molecules of water destroyed 

 in the formation of hydroxyl. 



Ordinary respiration, as already stated (Sec. 133), gives rise to energy, 

 or the power of doing work, and produces carbon dioxide and water. It may 

 also produce organic acids, imperfectly oxidized compounds, such as oxalic, 

 malic, and citric acids. These sometimes remain in the stems, leaves, or 

 fruit of the plant, as, for example, citric acid does in the citrous fruits 

 (lemons, limes, grape-fruits, oranges). Oxalic acid may be deposited as 

 insoluble crystals of calcium oxalate in various parts of the plant body, and 

 any of these acids may be mone completely oxidized and then excreted. 



The respiratory ratio, or relation of the volume of carbon dioxide pro- 



c*o 



duced to that of oxygen consumed, is usually nearly = 1. Some plants, 



2 



however, may at times give a very different result from this, as the Crassu- 

 lacece, in the dark, manufacture so much malic or other acids that little or 

 no carbon dioxide is given off. During the germination of oily seeds, while 

 the oil is being converted into starch, the respiratory ratio is usually less 

 than unity. 



1 See Peirce's Text-Book of Plant Physiology, Chapter n, Henry Holt & Co., 

 New York ; and Barnes' paper, " The Theory of Respiration," Botanical Gazette, 

 Vol. xxxix, pp. 81-98, 1905. 



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