FORMATION OF ORGANIC MATTER. 7 



The carbohydrate starch (C G H 10 6 ) is among the earliest 

 products ; it is an insoluble substance, and is converted 

 into sugar (glucose) for the nourishment of distant parts 

 of the plant, to which it is conveyed by the movement of 

 the sap. In parts where growth is taking place, and new 

 cells are being formed, the sugar of the sap is converted 

 into cellulose, the substance which forms the cell walls, 

 and of which the whole skeleton of the plant primarily 

 consists. The conversion of glucose into starch, or of 

 starch into glucose and cellulose, presents no chemical 

 difficulties, as all these eubstances are carbo-hydrates, 

 that is, they are composed of carbon and the elements 

 of water. 



The mode in which albuminoids are formed in the 

 plant is not certainly known ; probably the nitrates taken 

 up by the roots are converted into ammonia, the ammonia 

 into amides, and the amides finally into albuminoids. 



The fatty matter of a plant may be formed from 

 carbo-hydrates ; or possibly from the splitting up of 

 albuminoids. 



The vegetable acids in a plant are probably formed 

 by oxidation ; most likely by the oxidation of some 

 of the carbo-hydrates. 



We have just referred to oxidation as taking place in 

 the plant. This is always going on in the interior during 

 life, and as a result the plant is continually consuming a 

 small quantity of oxygen, and giving out a small quantity 

 of carbonic acid, an operation precisely similar to animal 

 respiration. This action is not readily perceived during 

 the daytime, being hidden by the opposite action of the 

 chlorophyll cells, which absorb carbonic acid and evolve 

 oxygen. If a plant is placed in darkness the respiratory 



