1917] SOILS FERTILIZERS. 627 



hydrolysis of the freshly precipitated form of phosphate, due partly to the 

 better physical condition. 



Great differences in the feeding powers of the different plants were observed. 

 It was found, as is shown in a previously noted article (E. S. R., 33, p. 519), 

 that plants containing a relatively high calcium oxid content showed a rela- 

 tively high feeding power for the phosphorus in raw rock phosphate, while 

 for plants containing a relatively low calcium oxid content the reverse was 

 true. The theory advanced to explain the variation in the feeding power of 

 plants for difficultly soluble phosphates (and other substances) is summarized 

 as follows : 



" Each point of contact or near contact between the absorbing surface of 

 root hairs and difficultly soluble substances may be regarded as a chemical 

 system which strives to attain a point of equilibrium between liquid and solid 

 phases. In this system carbonic acid and water are the main agents causing 

 solution. In some cases the action is largely one of hydrolysis and there is 

 formed a soluble product and an insoluble product, e. g., action of water on 

 ferric phosphate; in other cases the action may be both by hydrolysis and 

 carbonation and the products formed are both soluble, e. g., action of car- 

 bonated water on calcium phosphate; or only one of the products may again 

 be soluble, e. g., action of carbonated water on feldspar. 



" In order that the solubility reaction may continue in any of the cases, 

 it is necessary that proportionate amounts of all the soluble products be con- 

 tinually removed. Thus, if a plant is to feed strongly on rock phosphate, 

 both the calcium acid phosphate and calcium bicarbonate must be used by 

 the plant in somewhat proportionate amounts. In this case the calcium 

 oxid content of the plant becomes the determining factor in the feeding 

 power." 



" The increased availability of rock phosphate when used in connection 

 with ammonium salts is explained by this theory as due at least partly to 

 the increased solubility of the calcium carbonate and bicarbonate in solutions 

 of ammonium salts. The greater availability of rock phosphate in acid soils 

 than in nonacid soils, especially to plants with weak feeding powers, is also 

 explained, since acid soils will remove the calcium carbonate and bicarbonate 

 from solution and thus make it possible for the solubility reaction to continue." 



It is pointed out that since the roots of plants at any one time come in contact 

 with only a small portion of the internal surface of the soil, and the feeding 

 of plant roots therefore probably takes place largely in local soil areas, the 

 rate at which phosphorus goes into solution in the local areas in contact with 

 the roots is a more important consideration than the amount of it which may 

 be drawn off from the whole soil mass in one extraction. 



It was observed in these experiments that plants grown with magnesium 

 phosphate had an exceptionally high content of phosphorus, thus supporting 

 Loew's hypothesis (E. S. R., 15, p. 227) that magnesium functions as a con- 

 veyor of phosphorus in the plant. A high calcium oxid content was found in 

 certain cases to be associated with a high protein content, thus indicating 

 an important function of calcium in protein synthesis. Plants grown with 

 manganous phosphate were found to contain considerable amounts of manga- 

 nese, and since manganese affects the chlorophyll formation of certain plants, 

 especially of clover and alfalfa, it is suggested that the poor growth of these 

 plants on certain acid soils may be due to the presence of considerable amounts 

 of manganese. 



Report on commercial fertilizers, 1916, E. H. Jenkins and J. P. Street 

 (Connecticut State Sta. Rpt. 1916, pt. 1, pp. 1-63). — This bulletin contains the 

 results of actual and guarantied analyses of 828 samples of fertilizers and fer- 



