BACTERIZED PEAT 89 



and the second aerobic, working in the presence of 

 Oxygen. The former of these bacterial groups was 

 first described by Winogradsky in 1893, and was 

 named by him Clostridium pasteurianum. It is a 

 small rod-shaped organism, and can readily be 

 grown in solutions containing the requisite organic 

 food, such as sugar and mineral salts. But nitrog- 

 enous material must not be present. In such cir- 

 cumstances, if Oxygen is absent, it develops rapidly. 

 It can even grow in the presence of Oxygen, provided 

 other bacteria are mixed with it to take up the 

 Oxygen from the culture. After growing for a few 

 days there is no difficulty in showing that the 

 bacteria have added appreciable quantities of com- 

 bined Nitrogen to the medium in which they have 

 been developing. 



Several bacterial groups that are capable of fixing 

 Nitrogen in the presence of Oxygen have been 

 isolated. In 1901 Beyerinck described two species, 

 Azotobacter chroococcum and Azotobacter agilis. Three 

 additional species have since been described by Dr. 

 Lipman of the New Jersey Agricultural Experiment 

 Station. For the development of these bacteria a 

 good supply of air is essential, a fact that goes a long 

 way towards explaining why it is desirable for the 

 ground round the roots of plants to be kept well 

 aerated. A. chroococcum, the type with which we 

 are most concerned, is an egg-shaped organism with 

 a marked tendency to form agglomerations. It 

 requires for its development far less food material 

 than is needed by Clostridium, and flourishes best 

 in soil where lime is abundant. When cultivated by 



