CHAPTER IX 



RESPIRATION AND FERMENTATION 



76. The Role and Nature of Respiration.— Heretofore, the 

 metabolism in plants has been considered as a process through 

 which complex organic reserve substances decompose into their 

 elementary constituents. These simple parts are then again 

 formed into complex compounds of the protoplasm. No consider- 

 ation has been given to the highly important fact that in the second 

 synthetic stage of metabolism a considerable portion of the sub- 

 stances does not serve in the construction of new living matter, but, 

 on the contrary, undergoes a still further disintegration and leaves 

 the organism as end products of oxidation — carbon dioxide and 

 water. This loss of substance is especially evident when seeds are 

 germinated in darkness. By his classical investigations, Bous- 

 singault (1868) showed that seeds may lose in this manner over 

 half of their weight. In one of his experiments, grains of wheat 

 before germination weighed 1.665 g. but the seedlings developing 

 from them only 0.712 g., thus showing a loss of 57 per cent. Again, 

 seeds weighing 2.237 g. produced seedlings weighing only 1.076 g., 

 having lost 52 per cent of the original weight. 



This loss of substance is not equally distributed between the 

 different constituents of the seed. While the quantity of carbon, 

 hydrogen, and oxygen is continually decreasing, that of nitrogen 

 and of the mineral substances usually remains constant; hence, 

 the conclusion may be drawn that only substances which contain 

 no nitrogen decrease in amount, especially the carbohydrates. 

 This is shown diagrammatically by Prianishnikov (Fig. 100). It 

 will be noted from this figure that in germinating vetch seeds the 

 quantity of nitrogenous substances, in spite of the disintegrations 

 of proteins, remained the same, owing to the accumulation of 

 amino acids and asparagine. The amount of carbohydrates, how- 

 ever, decreased rapidly, since the soluble carbohydrates formed 

 in hydrolysis of starch are used only in small amounts for the con- 

 struction of cell walls. The greater part disappears. 



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