GERMINATION. ' 263 



and the oxygen and hydrogen which it contained 

 unite with the elements of the vegetable matter, and 

 form carbonic acid, ammonia, carburetted hydrogen, 

 and other substances. 



686. The first chemical change which takes place 

 in a germinating seed, is the change of a portion of 

 its azotized constituents into diastase (360), a sub- 

 stance which does not exist previously in seeds, but 

 is formed by the process of germination : it appears 

 to be a peculiar modification of vegetable albumen. 



This change cannot be effected without the pre- 

 sence of free oxygen, which removes the excess of 

 carbon. The azotised matter converted into diastase 

 immediately begins to act as a kind of ferment, 

 causing the starch and gum of the seed to pass into 

 the state of sugar. During the earliest stage of 

 germination, a small portion of vinegar or acetic acid 

 is formed. Alkalies tend to assist germination, be- 

 cause they combine with and neutralize this acid. 



687. The chemical changes attendant on the pro- 

 cess of germination, are very different from those 

 which go on during the growth of a complete plant. 

 Before the formation of leaves, and in the very ear- 

 liest stages of its growth, a plant requires only 

 warmth, moisture, and the presence of air ; but sub- 

 sequehtly, it requires, in addition to these, carbonic 

 acid and light. 



688. It is the oxygen of the air alone which is 

 essential to the germination of seeds, for the nitro- 

 gen being unable to combine with carbon, under or- 



