70 NUTRITION IN VEGETABLES. 
245. Lime is of great value in the improvement of soils. 
By its caustic nature, or its affinity for carbonic acid and 
water, it assists in decomposing the various organic matters 
in the soil; it acts as a stimulus to the absorbents of the 
root; and, by its firmness and cohesive properties, while at 
the same time it is not stiff and tenacious, forms an excé 
lent addition to either a sandy or an argillaceous soil. Itis | 
particularly adapted to thin marshy soils, which are unable 
to retain the organic matters which are decomposed. 
by the quantity of calcareous earth which it contains, acts 
the same way as lime, though less vigorously. 
246. Ploughing breaks down the earth ; exposes it and the — 
various organic substances in the soil to the action of the 
atmosphere, the oxygen in which aids in the decomposition 
of any organized matter which may be present; and mixes 
thoroughly the different ingredients in the soil. 
247. Manure enriches the soil by supplying the most 
sential matter for the nutrition of vegetables, decayed ant 
and vegetable matter. Soils which have become exhav 
that is, which have been deprived of their organic i 
ents by a succession of crop8, require to be invigorated | 
the admixture of more organic substances. This is done by 
means of manure, which is composed of the necessary 
terial,—carbon, oxygen, and hydrogen, &c., and in which. 
putrefactive process has made such progress, that it is in aD 
apt state for having its cohesion destroyed, and being reduced 
- to its pristine elements. It is rendered soluble in water, 
which state it is ready for being assimilated to the v 
248. This decomposition of the organic substances in 
__ soil is effected partly by means of the water and other 
present there and by the air (assisted by the influence 
_ heat), and partly by the reaction of the elements on ee 
other, or putrefaction. The water also acts the part 
solvent. Owing to the presence ot siirogte andt 
— animal: robatenpgt a 
