274 BOTANY PART i 



as driving power. Practically, however, it is found that the plant 

 proceeds to store up the energy of the sun's rays in the form of 

 potential chemical energy, and then utilises this at need. 



In intramolecular respiration also energy is set free ; this does not, 

 however, suffice in most organisms to maintain the driving force for 

 the vital processes. Some seeds can remain alive for many hours or 

 days with intramolecular respiration, and some even continue to give 

 off the same amount of carbon dioxide as in ordinary respiration. 

 In most cases, however, the amount of C0 2 rapidly diminishes. 

 In other plants death soon occurs, probably owing to the reduced 

 compounds acting as poisons. The value of intramolecular respiration 

 is in these cases only slight. On the other hand it has a" very great 

 importance in certain organisms which will be referred to later. 



B. OXIDATION OF INORGANIC MATERIAL ( 47 ) 



While most plants use organic compounds, especially carbohydrates, 

 in respiration, certain Bacteria utilise other sources of energy. Thus, 

 the nitrite bacteria which commonly occur in the soil oxidise ammonia 

 to nitrous acid, and the associated nitrate bacteria further oxidise the 

 nitrous acid to nitric acid. By the help of the energy thus obtained 

 they can then as has already been pointed out on p. 254 assimilate 

 carbon dioxide ; the chemical energy takes the place in them of the 

 sun's energy for the typical autotrophic plant. There is no breaking 

 down of organic material so that the whole of the assimilated nutri- 

 tive substance is retained, and the working of these organisms is very 

 economical. Since, however, only a limited amount of ammonia is 

 available, and this is derived from other organisms, they cannot take 

 the dominant place in nature which the green plants do. 



With the nitro bacteria the so-called sulphur bacteria may be associated ; these 

 oxidise sulphuretted hydrogen to sulphuric acid, sulphur being an intermediate 

 product, and being stored in the body of the plant. In the same way as the 

 sulphur bacteria utilise the energy set free in the oxidation of sulphuretted 

 hydrogen, the iron bacteria obtain usable energy by the oxidation of ferrous to 

 ferric oxide, other bacteria by the oxidation of methane to carbon dioxide and water, 

 and yet others by that of hydrogen to water. 



G. FERMENTATION ( 48 ) 



With the removal of oxygen intramolecular respiration begins, but 

 this cannot supply the necessary energy to maintain life in the higher 

 plants, although it may do so in lower organisms. Many Bacteria, 

 Fungi, and certain Algae (Characeae) are notably independent of a 

 supply of oxygen ; they succeed with slight traces of this gas, or they 

 avoid it altogether and live in situations where oxygen is absent. 



