INSTITUTE AND COLLEGE, PUSA, POP 1913-14. 87 



week, and which is still in progress, shows small irregular 

 variations. The amounts are of the same order as those 

 obtained by Ashby at Rothamsted and by Sackett in 

 Colorado. 



Pure Cultures. — The amount of nitrogen fixed by pure 

 cultures of Azotobacter isolated from Pusa soil was 

 increased by the additions of basic slag or humus to the 

 ordinary medium but was diminished by the substitution 

 of magnesium carbonate for calcium carbonate. The 

 amounts of nitrogen fixed in the pure cultures are similar 

 to those obtained by other investigators in Europe and 

 America. 



Well marked differences were observed in the morpholo- 

 gical and cultural characters of species of Azotobacter 

 isolated from Pusa, Cawnpore, Darjeeling and Bangalore 

 soils, and the amounts of nitrogen fixed by these also varied. 



A few preliminary experiments on nitrogen fixation in 

 the soil were carried out. 



The addition of a seer of cane sugar to a plot two square 

 yards in area, resulted in an increase, in the nitrogen con- 

 tent of the first six inches of soil, of nearly fifteen per 

 cent, in 10 weeks. 



The stimulation of nitrogen activity by the addition of 

 soluble carbohydrates may possibly be of considerable prac- 

 tical importance in the future. It has been shown by Koch 

 that certain bacteria can form soluble carbohydrates from 

 cellulose which can be used by Azotobacter as a source of 

 energy for nitrogen fixation; this action would briDg the 

 organic matter content of the soil into immediate relation 

 with its possible gain of nitrogen from the air. 



Some interesting results were obtained in connection 

 with work on bacterio-toxins in soil ; it was found possible 

 to measure the relative toxicity of various bacterial species 

 to an intermediate form (B. prodigiosus) and to one another, 

 by use of plate cultures and the measurement of the rate of 

 C0 2 formation in solid and liquid media, and the effect 

 upon the latter of the antagonism or symbiotic action as 



