ACCESSORY FOOD BODIES 113 



was used for the experiment. Nine flasks were 

 taken and divided into sets of three. The same 

 culture solutions were placed in all three flasks 

 i gramme of Mannite, 0-2 gramme of Di-potassium 

 phosphate (K 2 HPO 4 ), 0-02 gramme Magnesium sul- 

 phate (MgSO 4 ), and 0*2 gramme Calcium carbonate 

 (CaCO 3 ). The first three flasks had nothing in 

 addition, the second three received 0-00017 gramme 

 of the Phosphotungstic acid fraction that is, the 

 amount obtained from i gramme of treated peat 

 and the third set received a corresponding fraction 

 of the Silver nitrate fraction, the amount being 

 0-000035 gramme. Two flasks were sterilized to act 

 as a control. At the end of ten days no nitrogen 

 had been fixed in the sterilized flasks, 3-9 milli- 

 grammes had been fixed by the first series, 9-7 milli- 

 grammes by the second, and 10-4 milligrammes by 

 the third. 



In view of the encouraging results obtained in 

 these experiments it was decided to 'ascertain more 

 definitely how far liquid cultures of nitrifying 

 organisms* could be used as a test for the auximones. 

 A culture was originally obtained by incubating 

 garden soil in Winogradsky's medium. Two sub- 

 cultures were taken from this initial culture, and 

 eighteen flasks were filled with pure uninoculated 

 culture solution (Winogradsky's). These were all 

 inoculated with material from the second sub- 

 culture. The first series received nothing in ad- 

 dition, each flask of the second series received 



* These are organisms which have the property of converting 

 Ammonium salts into nitrates. 



8 



