16 MALXE STATE COLLEGE 



The influence of the soluble phosphoric acid was in the direction 

 of early maturity because it induced prompt early growth, but it 

 was not true in all instances that the final growth from this form 

 of acid was very much or even any greater than from the •water-in- 

 soluble forms. The plants grown on the soluble acid certainly were 

 the earliest plants to mature, even though they finally grew 

 no larger than some others. This fact is one of greater importance 

 in the production of crops out of doors during a short season, than 

 in the forcing* house where the season maybe indefinitely lengthened. 



(2) The water-insoluble forms of jmosphoric acid were used more 

 or less freely by all of the eight species of plants grown. This was 

 true both with the crude Florida rock and with the phosphates of 

 iron and alumina, although the phosphoric acid from the ground 

 Florida rock appeared to be the more freely used in a majority of 

 cases. While as we shall see later, this availability of the water- 

 insoluble phosj hates varied greatly with different species of plants, 

 it was sufficient in most instances to induce a material increase of 

 growth, it is clear, however, when we consider that nearly all of the 

 phosphoric acid of the phosphates of iron and alumina was soluble 

 in ammonium citrate, that in these experiments, at least, the avail- 

 ability of the water-soluble phosphoric acid differed greatly in degree 

 from the citrate-soluble. The present custom of classifying the 

 water-soluble and citrate-soluble phosphoric acid of our fertilizers 

 together as available does not appear to be rational in the light of 

 these experiments. 



(3) The solubility of a phosphate in an ammonium citrate solu- 

 tion at sixty-five degrees C did not in these experiments give a correct 

 measure of the relative availability of the phosphoric acid after ap- 

 plication to the soil. 



Two mineral phosphates were used in these experiments, one being 

 Florida rock, containing 2.46 per cent, of phosphoric acid soluble in 

 an ammonium citrate solution at sixty-five degrees C, the other being 

 the so-called Eedonda phosphate, consisting chiefly of hydrated phos- 

 phates of iron and alumina, which, after dehydration, contained 42.77 

 per cent, of phosphoric acid soluble in ammonium citrate. In the one 

 case only seven per cent, of the phosphoric acid was soluble in the 

 citrate solution, while in the other case eighty-six per cent, of the 

 phosphoric acid was soluble in that liquid. If the citrate soluble 

 phosphates are actually readily available to plants both before and 

 after entering the soil, then the dehydrated Eedonda rock should 

 have been greatly superior to the Florida rock as a source of plant- 

 food. This did not prove to be the case, the fact being that the 

 Florida rock proved to be the more useful. Any impartial observer 

 who watched these experiments must have been convinced that in a 

 majority of cases the plants were feeding more readily upon the 

 Florida rock than upon the other material and the figures reached 

 substantiate this conclusion. Onlv with the barlev and corn did the 



