METABOLISM. 31 



the interval between the securing of a grain of 

 starch, representing so much energy won from the 

 external universe, and the reconversion of this 

 grain into its equivalent carbon-dioxide and water, 

 by respiration, resulting in the loss of the above 

 energy as heat, the starch referred to may have 

 undergone numerous transformations in the living 

 machinery of the plant, and have played at various 

 times a role in connection with the most various 

 evolutions of energy. 



If we try to picture a possible case, we may take 

 the following. A given starch-granule, after being 

 built up in the chlorophyll-corpuscle, is decom- 

 posed, and yields part of itself as glucose, which 

 passes down into other parts of the plant in 

 solution. Part of it is merely re-converted into 

 starch, and temporarily stored : another part 

 passes into the arena of oxydation-processes, the 

 sum of which constitute respiration, and may serve 

 for a time in the molecules of an organic acid : 

 yet another part may be converted into a constitu- 

 ent of the cellulose cell-walls ; while part may be 

 brought into play in the reconstruction of pro- 

 toplasm. 



In this last connection a discovery made by 

 Schulze about 1878, and followed up later by 

 Pfeffer, Palladin, and others is of importance. 

 Seedlings growing in the dark, or in an atmosphere 

 devoid of carbon-dioxide in the light, become 

 surcharged with nitrogenous bodies known as 

 amides, formed during the breaking down of the 

 proteids in the destructive process preceding and 



