208 
THE COTTAGE GARDENER. 
[January 2 
Returning to the consideration of the food obtained by 
a plant from the soil by the agency of its roots, we find 
that silica, or the pure substance of flint, is present in 
all soils; is soluble in water, requiring one thousand 
j times its weight of this liquid to dissolve it (Kirwans 
! Mineralogy, vol. i. p. 10); is found in many plants, and 
in all the grasses that have been analysed. Alumina, or 
the basis of clay, present in all soils, is so soluble in 
; water as to he inseparable by the filter, and is much 
more so when any of the acids are present ( Sennebier’s 
j Physiology. Veget. vol. iii. p. 18); it is found in plants 
| in minute quantities, especially in the grain of barley, 
i oats, wheat, <Scc. ( Schrceder , in Gelden's Journ. vol. iii. 
! p. 525.) Lime is found in almost all soils; it is easily 
j soluble in water, and there is but one plant that is not 
} known to contain some of it as a constituent, the Salsola 
Soda. (Ann. de Chimie, vol. xviii. p. 76.) Magnesia, 
generally present in soils, is soluble in water, and is 
found in many plants. Iron is present in all soils, in all 
natural waters, and in all plants. Manganese is found 
in some soils, is soluble in water containing acids, &c., 
and is found in a few plants. But none of those sub¬ 
stances in a state of purity, either simply or combined, 
have ever been found capable of perfecting a plant 
through all its stages of growth, when moistened only 
with distilled water; the contrary is the case, however, 
when the water contains in solution vegetable or animal 
matters, as the dung of animals. Now these matters 
contain carbon, hydrogen, oxygen, nitrogen, and various 
salts: the three first are absolutely necessary for the 
existence of all plants, every part of which is chiefly 
composed of them; nitrogen is found in most plants; 
and the importance of salts to vegetation is demonstrated 
by the facts, that clover will not flourish where there 
is no sulphate of lime; that nettles follow the footsteps 
of man for the nitrate of potass, which always abounds 
near the walls of Ills habitation, and that marine plants 
linger for the common salt of their native haunts. Salts 
of some kind or other are found in every species of 
plant, but none of which the constituents have not also 
been detected in soils. During decay, vegetable and 
animal matters also exhale various gases. Carbonic 
acid, hydrogen, carburetted hydrogen, ammonia, &c., are 
of the number, all of which have been applied to the 
roots of plants with great benefit by Sir II. Davy and 
others. 
Although plants will not grow upon soils composed of 
the earths only, yet these have a great influence over 
plants, not merely by their secondary powers of regu¬ 
lating the amount of moisture, heat, &e., but by entering 
directly into the constitution of the plant; for it is a 
result of experience, to which we know of no exception, 
that a plant contains more of any given earth, if grown 
in a soil where it predominates, than if grown in 
a soil where it is in less abundance. This fact was first 
pointed out by Saussure, who found that the Rhododen¬ 
dron ferrugineum, when growing on the calcareous for¬ 
mation of Mount Jura, contained in its ashes 43.25 per 
cent, of carbonate of lime, hut only 0.75 of silica. On 
the other hand, the ashes of the same plant, from the 
granitic district of Mount Brevere, contained 2.0 per 
cent, of silica, but only 10.75 of carbonate of lime. 
However varying in the proportions, yet every soil is 
composed of silica, alumina, lime, magnesia, oxide of 
iron, salts, and animal and vegetable remains. The 
most important consideration is, what proportions those 
are which constitute a fertile soil. 
The bean ideal of a fertile soil is one which contains 
such a proportion of decomposing matter and of mois¬ 
ture, as to keep the crop growing upon it always supplied 
with food in a state fit for its consumption, yet not so 
superabundantly as to render the plants too luxuriant, 
if the object in view is the production of flowers or seed: 
but, for the production of those plants whose foliage is 
the part in request, as spinach, or of edible bulbous 
roots, as onions, which have a small expanse of leaves, 
so as to be almost entirely dependent upon the soil for 
nourishment, there can scarcely he an excess of decom¬ 
posed matter presented to their roots. Spinach, on rich 
soils, will yield successive cuttings the same as aspa¬ 
ragus : the latter, especially, demands abundant appli¬ 
cations of nourishment to its roots ; since, like the 
onion, it has little foliage and slightly fibrous roots, at 
the same time that it has to afford repeated cuttings; 
and thus, requiring a repeated development of parts, 
needs abundant food in its immediate neighbourhood. 
A soil with a just proportion of decomposing matter, 
will be capable of absorbing moisture during the droughts 
of summer from the atmosphere, for the most fertile soils 
are always the most absorbent, yet it must not be too 
retentive of moisture, which is the case in such soils as 
contain too much alumina; neither must it too easily 
part with moisture, a fault which is a characteristic of 
those soils which contain an excess of silica. A subsoil 
of gravel mixed with clay is the best, if not abounding 
in oxide of iron, for clay alone retains the moisture on 
the arable surface in too great an excess; and sand, or 
chalk, on the contrary carries it away too rapidly. It is, 
however, evident, that to insure these good qualities in 
any soil, at all seasons, is impossible; and it is as mani¬ 
fest that a soil that would do so in one climate would 
fail in another, if the mean annual temperature of them 
should differ, as well as the amount in inches of rain 
which fall during the same period. Since, in the western 
parts of England, more than twice as much rain occurs 
as in the most eastern counties, or in the proportion of 
42 to 19, a soil in the east of England, for any given 
crop, may he richer and more tenacious than the soil 
required for it on the western coast. 
Alumina, or clay, imparts tenacity to a soil when 
applied; silica, or sand, diminishes that power; whilst 
chalk and lime have an intermediate effect. They 
render heavy soils more friable, and light soils more 
retentive. These simple facts are important; two neigh¬ 
bouring gardens, by an interchange of soils, being often 
rendered fertile, which, before, were in the extremes of 
heaviness and lightness. 
From these statements it is evident, that no universal 
standard, or recipe, can be given for the formation of a 
fertile soil; but a soil, the constituents of which approach 
