THE METABOLISM OF PLANTS. 2O5 



just learned that the evolution of carbon dioxide in normal 

 metabolism is to be attributed to the oxidation and decom- 

 position of protoplasm, the decomposed protoplasm breaking 

 up into nitrogenous and non-nitrogenous (especially carbon 

 dioxide and water) substances of simpler composition, and 

 that, under ordinary conditions, the volume of carbon dioxide 

 evolved in a given time is approximately equal to, or rather 

 smaller than, the volume of oxygen absorbed. But if this 

 process were to go on without any corresponding constructive 

 process, the whole of the protoplasm would in a short time 

 be decomposed. We already know, however, that the plant 

 can construct protoplasm from the nitrogenous residues of 

 previous decomposition together with carbohydrates, and it 

 is shewn by Sachsse's analysis that the amount of proteid 

 matter in the peas was approximately the same after as 

 before germination. It is evident, therefore, that a con- 

 struction of protoplasm must have accompanied the germi- 

 nation, and it is an obvious inference that this construction 

 of protoplasm was effected at the expense of the starchy 

 reserve-materials. The absorption of oxygen and the evolu- 

 tion of carbon dioxide by the seed is, then, to be attributed 

 to the oxidation and decomposition of protoplasm, and the 

 disappearance of starch is due to its having been used in the 

 reconstruction of protoplasm. 



This explanation is not only satisfactory as regards this 

 special case, but it enables us to account also for certain facts 

 which we shall now consider. It has been already mentioned 

 (p. 173) that the germination of an oily seed is accompanied 

 by a disappearance of fat and a formation of starch, and it has 

 been observed/first by de Saussure and subsequently by many 

 others, that, in the course of germination, the absorption of 

 oxygen by these seeds is very much greater than the exhala- 

 tion of carbon dioxide. In the early stages of germination, 

 according to Godlewski, this is not the case; it is only when 

 fat is being replaced by starch at the time when the radicle is 

 beginning to protrude that the inequality of volume first 

 manifests itself, and it gradually diminishes as the fat disap- 

 pears from the seed. 



