176 OUTLINES OF BACTERIOLOGY 



may not be favourable to, say, Clostridium. The reader will readily 

 see what a large amount of patient research is still necessary before 

 we know all the possible combinations of these bacteria with algae 

 which will produce the best results. 



It was found, for instance, that whereas nitrogen-fixation resulted 

 when either of the two algae, Cystococcus and Nostoc punctiforme, 

 was added to a solution containing some earth-bacteria, this fixation 

 did not take place when, instead, either of the two algae Schizothrix 

 lardacea or Ulothrix flaccida was employed. 



3. It is important to remember that the amount of fixation is closely 

 governed by the amount of carbonaceous material supplied to the soil. 

 This can be seen from the following table. 



GAIN OF NITROGEN. 



1 litre nutrient solution contained 1 gram Glucose, 7 -4 mgr. 



9 1 3-^ 



5) 55 55 - 1 55 L ^ 55 



55 55 55 3 ,, 17'0 ,, 



4 31-4 



5 39-4 



6 45-9 



7 ^Q-Q 



J5 55 55 55 J U 55 



10 01-4 



>5 55 55 iU 55 55 



1 <> 1'27 >C ) 



55 55 A -' 55 



15 62-9 



In this series the nitrogen-fixing organism was Azotobacter. 



4. The process takes place in the dark as well as in the light, as 

 these bacteria are to be found over 100 cms. under the surface. 



5. It is agreed by all observers that the fixation of nitrogen is con 

 siderably hindered by the presence already of a large quantity of 

 nitrogen compounds in the nutrient substance. But it has been 

 affirmed that the presence of a small quantity of nitrogen is favourable 

 rather than otherwise to the fixation of nitrogen. 



6. With regard to temperature, it is stated that the process does not 

 take place under 10 C., and not over 40-50 C. 



The increase in the nitrogen content of one kilogram of earth has 

 been estimated to be as follows : 



From May 29th to Oct. 10th, - - 0-0709-0-0933 gr. 

 Oct. 10th to Apr. 30th, - 0-0933-0-0910 



Apr. 30th to Oct. 10th, - 0-0910-0-1179 



7. The presence of much water in the soil is to be carefully avoided. 

 When the percentage of water is more than 15, the fixation of nitrogen 

 begins to suffer. 



