2:u Classification of Pfant Food Elements in the Soil.—Thr plant- food elements of the soil occur principally as follows: 1. Nitrogen is found in soils as a constituent of organic matter, nitrates, a*xxruouium salts and aniino acids. 2. Phosphorus js present jn organic forms or combined with calcium, iron or aluminium as phosphate. 3. Potassium js widely distributed in all soils of granitic origin. It is combined with silica as silicates in granite, ortho- clase and trxica. 4. Calciuxn is found as carbonate and silicate, as sulphate In gypsum, as a constituent of rock phosphate and in organic forms. 5. Sulphur occurs combined with calcium as gypsum. It Is quite deficient in some soils. 6. Iron and manganese are found as oxides and silicates. 7. Magnesium is associated with calcium as dolomitic stone, also as silicates. Aluminiuioti, sodium and silicon are probably non-essential to plant growtli. Value of Soil Analysis.-—There has been much concerning -fclie adequacy of soil analysis as a means of soil fertility. Many writers confuse the narrow purpose of simply deterj^mining the plant food immediately available with the broader one of obtaining an extensive knowledge of the plant food supply and a determination of the possible origin of the soil in order to plan better for permanent improve- ment. The "value of the analysis is expressed by Hopkins1 as follows: "The chief "value of a chemical analysis is to serve as an absolute foundation upon which methods of soil treatment can safely be for the adoption of a system of permanent soil enrichment, not for crop or for one year only but for progressive improvement/" . The Ohio Station has shown2 how accurately the excesses : ftp] deficiencies may be measured by analysis when good and poor : ||| methods of sericulture have been practiced for a period of fifteen ||] years. Thore is no other tool which compares with it for |. ] purpose and as an aid in unlocking soil secrets. The value of I ! 1 "Soil Fertility and Permanent Agriculture," p. 568. ml \ 2 Ohio Exp~