f plant-food, is of the highest
importance. We cannot do better, therefore, than discuss its properties
under the headings _mechanical_, _chemical_, and _biological_.

I. MECHANICAL FUNCTIONS OF LIME.

_Action on Soil's Texture._

The effect of lime upon the texture of a soil is among its most striking
properties. Every farmer knows well what a transformation is effected in
the texture of a stiff clay soil by the application of a dressing of
lime. The adhesive property of the soil--its objectionable tendency to
puddle when mixed with water--is greatly lessened, and the soil is
rendered very much more friable when it becomes dry. Several reasons
exist for this change. In the first place, the tendency to puddle in a
clayey soil is due to the fine state of division of the soil-particles.
The way in which lime counteracts this adhesive property is by causing a
coagulation of the fine soil-particles. This flocculation or aggregation
of the fine clay-particles, when mixed with water by lime, is strikingly
demonstrated by adding to some muddy water a little lime-water. The
result will be that the water will speedily be rendered clear, the fine
clay-particles coming together and sinking to the bottom of the vessel.
Even a very small quantity of lime will effect this change. This
property possessed by lime, we may mention, is utilised in the treatment
of sewage. As it is the fine clay-particles that are the chief cause of
the puddling of clay soils, their flocculation does much to destroy this
objectionable property. Another reason why lime renders a clay soil more
friable when dry is, that lime does not undergo any shrinkage in dry
weather. As clay soils shrink very much in drying, the mixture with such
a substance as lime tends to minimise this tendency to cake in hard
lumps. The effect of even a very small addition of lime to a clay soil,
in the way of increasing its friable nature, is very striking, and can
be easily illustrated by taking two portions of clay, into one of which
a small percentage of lime is introduced, and working both into a
plastic mass with water, and then allowing them to dry. It will be found
that while the one is hard and resists disintegration, that portion to
which the lime has been added crumbles away easily to a powder. This
effect which lime has in "lightening" heavy soils has been known to last
for years. The disintegrating effect of quicklime when applied to heavy
soils is also due, it may