174 BOTANICAL GAZETTE [MARCH 
The acids produced by bacteria act upon various phosphates, 
changing them to the soluble monophosphate, but the rate of solu- 
tion varies widely with the different compounds. ‘Tricalcium 
phosphate, in precipitated form, dicalcium phosphate, and tetra- 
calcium phosphate of Thomas slag are much more rapidly dissolved 
than the crystalline or the so-called amorphous phosphates. The 
general reaction is as follows: 2RCOOH+Ca,(PO,),=Ca,H 
(PO,).+(RCOO),Ca. The reaction takes place most aaa 
in soils containing large quantities of organic matter due to the 
active fermentation taking place in such soils. 
Grazia (6) considers enzyme action to play a part in the 
dissolving of phosphates in soil, for he found the addition of chloro- 
form to a soil reduced bacterial activity and decreased the acid 
produced, but at the same time the solution of phosphates was 
increased. This is in keeping with the finding of BycurkHIN and 
SKALSKI (4). 
The presence of ammonium chloride and sulphate in the 
cultural media is especially effective, according to PrRorti (25), in 
increasing the solvent action of bacteria for phosphorus. PEROTTI 
considers the successive steps in the solution or decomposition of 
phosphorus in bacteria cultures to be as follows: (1) generation 
of acids, (2) secondary reactions in the solution, and (3) production 
of a soluble phosphorus containing organic substance. The 
two of these are the result of the activity of the bacteria on the 
phosphorus, and the last is due to the metabolic assimilation of 
the microorganisms. 
The oxidation of sulphur by soil bacteria at times may generate 
sufficient acid to play a very important réle in the dissolving of soil 
phosphorus. Hopkins and Wurrtinc (15), however, consider that 
the nitrosomonus are of first importance in rendering phosphorus 
and calcium soluble, due to the nitrous acid produced from 
ammonia: (NH,),CO,+60=2HNO,+H.CO,+2H,.0. The result- 
ing nitrous acid reacts with the raw rock phosphate rendering it 
soluble, thus: Ca,(PO,).+4HNO, =CaH,(PO,),+2Ca(NO,):- 
Analyses showed that about one pound of phosphorus and 
about two pounds of calcium are made soluble for each pound of 
nitrogen oxidized, aside from the action of the acid radicles asso- 
