30 ON THE USE OF LIME, MARL, AND SHELL-SAND. 



inorganic or mineral constituents in an intimate state of combi- 

 nation. From this close union the mineral matters, however, 

 cannot be removed by water, even when they are as easily soluble 

 as potash or soda. As long as the organic tissue of the roots, 

 leaves, and other vegetable matters in the soil remain unaltered, 

 potash, soda, sulphuric and phosphoric acid, and other fertilizing 

 mineral matters which are united with them, will remain un- 

 available to the use of plants. But in the measure in which the 

 decomposition of the organic substances proceeds, the inorganic 

 are liberated and can then be applied to the benefit of the 

 growing plants. And as lime hastens the decomposition of all 

 organic matters, its beneficial effects upon vegetation partly, no 

 doubt, are attributable to the liberation of inorganic or mineral 

 fertilizing substances, which it promotes in a great measure. 



4. Lime exercises a beneficial effect upon the inorganic matters in 

 the soil. 



Although the effects of lime are most conspicuous on soils rich 

 in organic matters, it is not inactive on land deficient in such 

 matters. Lime not only facilitates the decomposition of organic 

 substances, but effects also important changes in the mineral 

 constitution of soils. In particular we would mention its effects 

 upon many silicates. By causing their decomposition in the 

 soil, lime sets free potash and soda, two substances highly con- 

 ducive to the luxuriant growth of many plants. 



In many soils, but especially in clay land, we find portions of 

 granite and other minerals from which clay has been originally 

 produced. These minerals are the chief sources from which the 

 necessary amount of alkalies, required by plants, is furnished. 

 But as their decomposition proceeds slowly, a long time must 

 pass before potash and soda can be set free. Lime materially 

 hastens this decomposition, and can be compared in this par- 

 ticular action to the effects which prolonged fallow produces 

 upon land. 



If it only acted beneficially in converting inert vegetable sub- 

 stances into actual fertilizers, the beneficial effect upon clays that 

 are nearly destitute of organic substances would be perfectly 

 unintelligible. This action, however, fully accounts for the 

 effects of lime upon clay land. 



We thus see that the action of lime on vegetation depends on 

 more than one cause ; and that consequently its effects in that 

 respect will be influenced by the various circumstances under 

 which it is applied to the land. 



At the same time, the four different functions which we have 

 mentioned as belonging to lime, point out to us the uses of lime 

 in agriculture, and the benefits which are likelv to result from 

 its application. 



