president's address — SECTION G (ll.)- 



229 



Turning next to pTiosphoric acid, we may look upon this constituent 

 -as being, in a special sense, the controlling factor in the development 

 -of plant life. It is remarkable that the world supply of nitrogen, 

 phosphoric acid, and lime at present, available for the use of existing 

 plants and animals has all been combined and rendered available by 

 past generations of living things. Originally, all the phosphoric acid 

 •of the soil formed part of the most ancient rocks in the form chiefly of 

 apatite. It has gradually become concentrated on the surface of the 

 soil by the intervention of plants and animals. Comparatively little 

 is leached out of the soil by the rain, only the barest trace being present 

 in sea water. In the case of rock phosphate, the seaweed growing in 

 shallow depths has collected this trace of phosphoric acid from the 

 sea water, just as the coral and other organisms have collected the lime, 

 or the copper sheathing of a ship causes the deposition of silver and 

 gold. From the seaweed the conversion into rock phosphate is accom- 

 plished through the medium of the fish and birds. We are at the present 

 time drawing on the accumulations that have been made in past geo- 

 logical ages. In the case of the phosphoric acid of the soil, this has 

 been gradually accumulating in the surface layers through the medium 

 of the plant, but its concentration is brought about through the inter- 

 vention of the animal. The nearly insoluble phosphate of lime of the 

 bones of vertebrates offers striking analogies to the similarly insoluble 

 •carbonate of lime of the shells of invertebrates. 



PECULIARITY OF AUSTRALIAN SOILS. 



The following table gives the result of analysis of 186 samples of 

 Victorian soil recently made in the laboratory of the Department of 

 Agriculture. For comparison, I append the results the averages of 

 10 types of English soil, made by Hall, and of a large number of Ameri- 

 can soils bv Hillgard. It will be seen that om* soils are well above the 

 recognised limit of efficiency as regards nitrogen (100 parts per 100,000), 

 but very close to the limit of inefficiency as regards phosphoric acid. 

 European and American authorities look on 50 parts per 100,000 as the 

 limit below which it becomes unprofitable to work the soil. It also 

 appears that our subsoil is nearly as rich in phosphoric acid as the surface 

 layers. Potash and lime are so abundant that they call for no comment. 



