FORMATION OF SUGAR. 137 



(Saussure) ; and further, that the sugar increases on the diminu- 

 tion of the acid ; we can scarcely avoid coming to the conclusion, 

 that the carbon of the organic acid in the unripe fruit becomes a 

 constituent of the sugar when it is ripe, and that, in consequence 

 of the separation of oxygen and the assimilation of the constitu- 

 ents of water, the acid passes into sugar. 



The tartaric acid in grapes, the citric acid in cherries and in 

 currants, the malic acid in summer apples, which ripen on the 

 trees, form in these plants the intermediate members of the pas- 

 sage of carbonic acid into sugar ; and when there is a deficiency 

 of proper temperature, or of the action of solar light, the changes 

 necessary for the conversion into sugar are not furnished, and the 

 acids remain. 



In the fruit of the mountain ash, malic acid succeeds the tar- 

 taric acid at first present, or in other words, an acid poor in oxy- 

 gen succeeds one rich in that element; afterwards the malic acid 

 in the berries disappears almost entirely, and in its place are 

 found gum and mucilage, neither of which formerly existed in 

 them ; and with the same reason that we consider that the carbon 

 of the tartaric acid forms a constituent of the succeeding malic 

 acid — and this few would be inclined to dispute — we suppose that 

 the carbon of the acids passes over into the sugar which succeeds 

 on their disappearance. 



It surely cannot be supposed that a plant assimilates carbonic 

 acid, and that this carbonic acid is converted in the organism of 

 the plant into tartaric, racemic, and nitric acids, merely for the 

 purpose of being reconverted into carbonic acid. 



If then the view be confirmed, that the organic acids in culti- 

 vated plants aid in the formation of sugar, it must be admitted 

 that they are of equal importance in the production of all other 

 non-azotized ingredients similarly composed. The formation of 

 starch, of pectin, and of gum, does not take place immediately, that 

 is, they do not arise at once from the union of the carbon of the 

 carbonic acid with the constituents of water ; but a gradual con- 

 version takes place, in consequence of the production of com- 

 pounds that are always poorer in oxygen, and always richer in 

 hydrogen. We cannot suppose that oil of turpentine could be 



