380 SOILS. 



neutral humus, and (as shown in the case of the soils of the 

 arid region) the concentration of the nitrogen in the same; 

 while accelerating the oxidation of the carbon and hydrogen, 

 as shown by S. W. Johnson and others. 



6. It counteracts the deleterious influence of an excess of 

 magnesia in the soil, as first shown by Loew, 1 and verified by 

 his pupils in Japan. 



7. In alkali soils, according to Cameron and May, it coun- 

 teracts the injurious action of the soluble salts upon the 

 growth of plants, not only in the form of carbonate, but also in 

 those of sulfate and chlorid. 2 



8. As a matter of experience, both in the case of grapes and 

 orchard as well as wild fruits, an adequate but not excessive 

 supply of lime in the soil will produce sweeter fruit than when 

 lime is in small supply. 



9. An excess of carbonate of lime in soils (from eight to 

 twenty per cent and more), constituting " marliness," tends to 

 seriously disturb the nutrition and general functions of many 

 plants (calcifuge), and to produce a suppression or diminution 

 of the formation of chlorophyll and starch ; as in the case of 

 grape vines, citrus fruits and others, which nevertheless flour- 

 ish best in lands moderately calcareous. 



Among the points thus enumerated the third and fourth re- 

 quire some comment. Without pretending to define exactly 

 how lime acts in rendering other ingredients more available to 

 plant assimilation, attention may be called to the fact that lime 

 carbonate may be considered as acting similarly to, albeit more 

 mildly than, caustic lime, in the displacement of other bases 

 from their compounds. It doubtless acts thus in liberating 

 potash from its zeolitic compounds. As to phosphoric acid, 

 the connection of the effect of lime carbonate with the remark- 

 able availability of that substance when present in the form of 

 tetra-basic salt, in the case of phosphate slag, is at least possible. 



As to the action of lime carbonate in forming humus, 3 no one who 

 has observed the characteristic dark black tint of our calcareous 



1 Bull. No. I, Div. Veget. Physiol. and Plant Pathol. U. S. Dept. Agr. ; et al. 



2 Loeb (Publications of the Spreckel's Physiological Laboratory of the Univer- 

 sity of California, has shown a similar protective influence of the lime salts in 

 sea-water, against the other salts, in the case of the lower marine organisms. 



3 " Black Soils ; " Agric. Science, January, 1892. 



