SOWING. 
its being the vehicle by means of which a supply 
of air, and moisture, and warmth, can be con- 
tinually kept up. With this simple statement 
in view, we are quite prepared to consider the 
various conditions of soil, for the purpose of de- 
termining how far these will influence the future 
prospects of the crop; and we shall, accordingly, 
at once proceed to examine carefully into the 
mechanical relations of soil. This we purpose 
doing by the aid of figures. 
“Soil, examined mechanically, is found to 
consist entirely of particles of all shapes and 
sizes, from stones and pebbles down to the finest 
possible powder; and, on account of their ex- 
treme irregularity of shape, they cannot lie so 
close to one another as to prevent there being 
passages between them, owing to which circum- 
stance, soil in the mass is always more or less 
porous. If, however, we proceed to examine 
one of the smallest particles of which soil is made 
up, we shall find that even this is not always 
solid, but is much more frequently porous, like 
soil in the mass. A considerable proportion of 
this finely divided part of soil, the impalpable 
matter as it is generally called, is found, by the 
aid of the microscope, to consist of broken down 
vegetable tissue; so that when a small portion 
of the finest dust from a garden or field is placed 
under the microscope, we have exhibited to us 
particles of every variety of shape and structure, 
of which a certain part is evidently of vegetable 
origin. In these figures I have given a very 
rude representation of these particles; and I 
must beg you particularly to remember that 
they are not meant to represent, by any means 
accurately, what the microscope exhibits, but 
are only designed to serve as a plan by which to 
illustrate the mechanical properties of the soil._— 
On referring to fig. 1, we perceive that there are 
two distinct classes of pores,—Ist, the large ones, 
which exist between the particles of soil, and, 
2d, the very minute ones, which occur in the 
particles themselves; and you will at the same 
time notice, that whereas all the larger pores, 
those between the particles of soil, communicate 
most freely with each other, so that they form 
canals; the small pores, however freely they may 
communicate with one another in the interior of 
the particle in which they occur, have no direct 
connexion with the pores of the surrounding 
particles. Let us now, therefore, trace the effect 
of this arrangement. In jig. 1, we perceive that 
ters. 
277 
these canals and pores are all empty; the soil 
being perfectly dry, and the canals communicat- 
ing freely at the surface with the surrounding 
atmosphere, the whole will of course be filled 
with air. If, in this condition, a seed be placed 
in the soil, as at a, you at once perceive that it 
is freely supplied with air, but there is no mois- 
ture; therefore, when soil is perfectly dry, a seed 
cannot grow.—Let us turn our attention now to 
jig. 2. Here we perceive that both the pores 
and canals are no longer represented white but 
black, this colour being used to indicate water. 
In this instance, therefore, water has taken the 
place of air, or in other words, the soil is very 
wet. If we observe our seed a now, we find it 
abundantly supplied with water, but no air. 
Here again, therefore, germination cannot take 
place. It may be well to state here, that this 
can never occur exactly in nature, because water, 
having the power of dissolving air to a certain 
extent, the seed a in jig. 2 is in fact supplied 
with a certain amount of this necessary sub- 
stance; and, owing to this, germination does 
take place, although by no means under such 
advantageous circumstances as it would were 
the soil in a better condition—We pass on now 
to fig. 3. Here we find a different state of mat- 
The canals are open and freely supplied 
and consequently you perceive that, while the 
seed a has quite enough of air from the canals, 
it can never be without moisture, as every par- 
ticle of soil which touches it is well supplied 
with this necessary ingredient. This, then, is 
the proper condition of soil for germination, 
and in fact for every period of the plant’s de- 
velopment; and this condition occurs when soil 
is moist, but not wet; that is’ to say, when it 
has the colour and appearance of being well 
watered, but when it is still capable of being 
crumbled to pieces by the hands, without any of 
