STATE IN WHICH LIME EXISTS IN THE SOIL. 379 



2°. The results of all the chemical examinations hitherto made in 

 regard to the nature of the inorganic matter contained in the sap and 

 substance of plants indicate, — if not the absolute necessity of lime to the 

 growth of plants, — at least that in nature all cultivated plants do ab- 

 sorb it by their roots from tlie soil, and make use of it in some way in 

 aid of their growth. In so far as our practice is concerned, this is very 

 much the same as if we could prove lime to be absolutely indispensable. 



The ash of the leaf and bulb of the turnip or potatoe, of the grain 

 and straw of our corn-bearing plants, and of the stems and seeds of our 

 grasses, all contain lime whenever and wherever they are grown. And 

 most of them attain high health and luxuriance only where lime is 

 easily attained. 



Grant, then, that lime appears to be, perhaps virtually is, a necessary 

 food of plants, without which their natural health cannot be maintained, 

 nor functions discharged, — still the quantity which must be present in 

 the soil to supply this food is not necessarily large. Even in favor- 

 able circumstances we have seen (Lee. X., § 3,) that the average crops 

 during an entire rotation of four years may not carry off more than 250 

 lbs. of lime from the acre of land, a quantity which even the marsh 

 soils of Holstein would be able to supply for half a century, could the 

 roots readily make their way into every part of the soil. 



Still we may safely hold, I think, that this quantity of lime at least 

 is indispensable — if cultivated plants are to flourish and ripen. So 

 much, at least, must in practice be every year added to cultivated land 

 in one form or another, where the crops are in whole or in part carried 

 off the land. Where it is not added either artificially or by some natu- 

 ral process, infertility must gradually ensue. We shall presently see 

 that lime has other functions to perform in the soil, and that there are 

 natural causes in constant operation in our climate which render a 

 larger addition than this desirable at least, if not indispensable to con- 

 tinued fertility. 



§ 9. State of comhination in which lime exists in the soil. 



This lime, which we have concluded to be an indispensable constitu- 

 ent of fertile soils, may be present in several distinct states of combi- 

 nation. 



1°. In that of chloride of calcium. — This compound, as we have al- 

 ready seen (Lee. IX., § 4,) is very soluble in water, and is not unfre- 

 quently to be detected in the sap, especially of the roots of plants. Its 

 solubility, however, exposes it to be readily washed out of the soil by 

 the rains, and perhaps for this reason it is not one of those forms of com- 

 bination in which lime is recognised as a uniform or necessary consti- 

 tuent of the soil. Its presence may be detected by boiling half a pound 

 of the soil in distilled water, filtering and evaporating the solution to 

 dryness. If the dry mass become moist on exposure to the air, and if, 

 after being dissolved in water, it give a white precipitate with oxalate 

 of ammonia, and after being rendered sour by a few drops of nitric acid, 

 a white precipitate again with nitrate of silver, it may be inferred to 

 con-tain chloride of calcium. 



2°. In that of sulphate of lime or gypsum. — In this state also it is not 

 a constant, and in a few cases only an abundant, constituent of the soil. 



