72 ASSIMILATION OF 



effects indeed seem rather to be of a negative 

 quality than otherwise, resulting only in a de- 

 ficiency of power, in the various classes of 

 plants, to assimilate the carbon and exhale the 

 oxygen set free by such assimilation ; but in 

 the effects it produces in rendering other mat- 

 ter in a fit state to become or afford the pabulum 

 to plants, it is equally important with the gases 

 before named. 



All the oxygen gas set free in plants by the 

 assimilation of the hydrogen and carbon, in the 

 manner before noticed, appears under favoura- 

 ble circumstances, to be given off in its pure 

 state, but when such circumstances are not 

 favourable, when indeed the plant may be con- 

 sidered to be in an unhealthy state, from the 

 absence of a sufficient quantity of light to al- 

 low the assimilation of carbon and the decom- 

 position of the water, the oxygen then remains 

 in the plant, and enters into- combination with 

 the salts and other substances it may find 

 there, and gives its peculiar character, that of 

 acidity, to the products of the plant. 



A familiar proof of the effects of oxygen 

 under such circumstances, is the sour acid 

 taste and watery flavour which fruits possess 

 when clouds and rain, during a cold wet sum- 

 mer, intercept the sun's rays and prevent the 

 influence of light on the fruits. 



In this case the water absorbed by the root 

 of the plant exists in its watery state and gives 

 the vapid flavour, whilst the carbon imper- 

 fectly assimilated and the oxygen thus set free, 



