152 MASS. EXPERIMENT STATION BULLETIN 162. 



The table makes it strikingly apparent that the natural mineral (rock) 

 phosphates used in this series of experiments have produced much smaller 

 average increases in crops than those of the other classes. For the pur- 

 pose, however, of bringing out the relative effects more clearl^v the results 

 have been figured on a percentage basis shown in the table below: — 



