evolution of heat.

It appears to be a general, though not invariable fact, that dark
colored soils, other things being equal, are constantly the warmest, or
at any rate maintain the temperature most favorable to vegetation. It
has been repeatedly observed that on light-colored soils plants mature
more rapidly, if the earth be thinly covered with a coating of some
black substance. Thus Lampadius, Professor in the School of Mines at
Freiberg, a town situated in a mountainous part of Saxony, found that he
could ripen melons, even in the coolest summers, by strewing a coating
of coal-dust an inch deep over the surface of the soil. In some of the
vineyards of the Rhine, the powder of a black slate is employed to
hasten the ripening of the grape.

Girardin, an eminent French agriculturist, in a series of experiments on
the cultivation of potatoes, found that the time of their ripening
varied eight to fourteen days, according to the character of the soil.
He found, on the 25th of August, in a very dark soil, made so by the
presence of much humus or decaying vegetable matter, twenty-six
varieties ripe; in sandy soil but twenty, in clay nineteen, and in a
white lime soil only sixteen.

It cannot be doubted then, that the effect of dressing a light sandy or
gravelly soil with peat, or otherwise enriching it in vegetable matter,
is to render it warmer, in the sense in which that word is usually
applied to soils. The upward range of the thermometer is not, indeed,
increased, but the uniform warmth so salutary to our most valued crops
is thereby secured.

In the light soils stable-manure wastes too rapidly because, for one
reason, at the extremes of high temperature, oxidation and decay proceed
with great rapidity, and the volatile portions of the fertilizer are
used up faster than the plant can appropriate them, so that not only are
they wasted during the early periods of growth, but they are wanting at
a later period when their absence may prove the failure of a crop.

B. The ingredients and qualities which make peat _a direct fertilizer_
next come under discussion. We shall notice:

_The organic matters including nitrogen (ammonia and nitric acid)_ (I):

_The inorganic or mineral ingredients_ (II):

_Peculiarities in the decay of Peat_ (III), _and_

_Institute a comparison between peat and stable manure_ (IV).

I.--Under this division we have to consider:

1. _The organic matters as direct food to plants._

Thir