246 Report of tiie Department of Chemistry of the 



another. It should be remembered that the soluble salts, which 

 one would expect to be the main factor in modifying the chemical 

 status of the soil, were practically alike, added in practically 

 the same forms and in the same quantities with all the forms 

 of phosphoric acid and it seems hardly possible that a minute pro- 

 portion of the insoluble phosphates which are very slow to react, 

 would of itself so modify root environment as to cause the ob- 

 served differences in growth, not caused by differences in the 

 supply of available material. The most rational theory for ex- 

 plaining the foregoing data is that the roots of the various species 

 of plants do not react alike upon soil compounds. This conclu- 

 sion should not be regarded as condemning the use of insoluble 

 phosphates under all conditions. This line of inquiry is directed 

 toward the discriminating use of such materials. 



INFLUENCE OF FINENESS UPON THE AVAIL- 

 ABILITY OF RAW GROUND PHOSPHATES. 



During recent years there has been much discussion concern- 

 ing the usefulness of ground raw phosphatic rock as a fertilizer. 

 In this connection the influence of fineness upon the availability 

 of the phosphoric acid in this material is an important consid- 

 eration. 



Box experiments carried on in 1899-1900 and 1903-4 with 

 undissolved Florida rock ground to different degrees of fineness 

 have yielded interesting results which are worthy of permanent 

 record. 



PLAN OF EXPERIMENTS. 



The experimental plants were grown in the forcing house in 

 wooden boxes 15" x 15". In 1899-1900 the soil consisted of 

 quartz sand as follows: 46 lbs. of sand passed through a sieve 

 forty meshes to the inch, 8 lbs. of medium coarse and 4 lbs. of 

 coarse for drainage. In 1903-'4 the soil was also quartz sand 

 consisting of 31 lbs. of fine, 4 lbs. of medium, and 8 lbs. of 

 coarse for drainage; to the fine sand was added .93 lb. or 3 per ct. 

 of ground sphagnum moss. The moss was that which had grown 



