CANE SUGAR. 



moment accepted that, through the agency of certain bacteria, the nitrogen of 

 the air becomes fixed in the soil, and thus indirectly becomes available to the 

 higher plants ; the organisms that have been most studied in this connection are 

 the Clostridium pastorianum and the A%otdbacter chroococcum ; the latter is of 

 cosmopolitan distribution, ' varieties ' from different parts of the world show- 

 ing only minor differences ; a supply of calcium carbonate is probably essential 

 to its development, and the amount of nitrogen fixed is correlated with the 

 quantity of carbohydrate present. In this connection, and in special reference 

 to the cane sugar industry, Ebbels 17 has indicated the use of molasses as a 

 source of carbohydrate. Although it is now certain that nitrogen in the 

 form of ammonia can be assimilated by some higher plants, yet it is as nitrate 

 that the greater proportion is taken up ; the working out of the cycle, whereby 

 the plant takes up its nitrogen, is due to Schloesingand Muntz, to Warrington, 

 to Frankland, and especially to Winogradsky. As a result of their investiga- 

 tions it has been established that the formation of nitrates takes place in two 

 stages ; two types of organisms are employed in the first stage, one, classified 

 as nitrosomonas peculiar to the old, and the second as nitrosococcus occurring in 

 the new world. These organisms convert ammonia salts into nitrites ; the con- 

 version of the nitrite into nitrate is effected under the influence of an organism 

 called nitrobacter, which is cosmopolitan. The factors influencing the activity 

 of these organisms are briefly as under : 



1. The limits of activity are 5C. and 55C., with an optimum 

 temperature of 37C. 



2. Their activity is diminished by the presence of much organic matter, 

 and by the presence of alkaline chlorides and carbonates. 



3. A base is necessary to neutralize and combine with the acid formed ; 

 the most efficient base is calcium carbonate, but magnesia carbonate, and the 

 zeolites present in clay may also serve. 



4. A supply of oxygen, and of carbon is necessary ; the latter may be 

 derived from carbonates, or from the carbon dioxide of the air. 



5. A supply of water is essential, but not an excess, which is actually 

 harmful. 



6. Absence of direct sunlight. 



From the above it is seen that nitrification, and hence plant growth will 

 proceed best in a well tilled, well aerated, well drained soil, at a temperature 

 of about 37C. and in the presence of a supply of calcium carbonate. 



Conversely to the formation of nitrates, a degradation of these bodies 

 eventually to gaseous nitrogen occurs. This process known as denitrification 

 takes place under the influence of a variety of organisms, and the favour- 



82 



