48 GROWTH OF THE PLANT 



Here it may be changed into cellulose for cell walls, or 

 starch, sucrose, and oil for storage, etc. Some of the carbo- 

 hydrates are used as material for oxidation or respiration, 

 just as in the germinating seed. Oxygen is needed for 

 this process. Carbon dioxide and water are the products 

 of respiration. Energy is released, and heat, work, and 

 chemical compounds result. All the plant activities of 

 chemical change and reproduction are dependent on res- 

 piration. In some cases, and possibly quite generally even 

 under normal conditions, there is a so-called intermolecular 

 respiration whereby one molecule is oxidized at the expense 

 of another which is reduced. This respiration results in the 

 production of such compounds as acids and alcohols in addi- 

 tion to carbon dioxide and water. Energy is set free by 

 this process also. 



Probably as a result of this intermolecular respiration oils 

 are formed. They are at least made from carbohydrates — 

 dextrose largely — and contain less oxygen. They are storage 

 forms of food material. Proteins are built up from carbo- 

 hydrates, probably by a partial oxidation of them and 

 consequent reduction of nitrates and sulphates. These are 

 combined to form amides, albumoses, peptones, and finally 

 proteins. Phosphorus, or rather the phosphoric acid radicle, 

 is sometimes included in the protein molecule. Protoplasm — 

 the seat of cell life and activity— is largely protein with some 

 oil, carbohydrate, and mineral water. 



The seeds are the means of reproduction and contain 

 the embryo and the stored food for the embryo. This 

 food has been moved at maturity from the various parts 

 of the plant where it was made or temporarily stored, and 

 converted by enzyme action into a very concentrated anhy- 

 drous form of protein, oil, and starch. Some plants do not 

 produce seeds the first year; others live on from year to 

 year, and in these cases the food is not anhydrous but is 

 usually in hydrated forms like sucrose or dextrose. 



The various essential elements have special parts to 

 play in the phenomenon of plant growth. Carbon, hydrogen, 

 oxygen, nitrogen, sulphur, and phosphorus at least are 

 essential constituents of plant tissue. The other elements, 



