| ingredients. 
prived by the grain of a crop of corn, we have 
no such resource for a renewal of its mineral 
The phosphoric acid, the potash, 
and the magnesia of a plant must be obtained 
from the soil, and the soil alone. But even in 
this respect much may be done; it may be safely 
predicted that a time will come when, in the 
cultivation of land already brought into a state 
of high fertility, the application of artificial ma- 
nures, except in rare cases, will be looked upon 
as am unnecessary and unjustifiable waste of 
money. At the present stage of agricultural 
practice, the only necessary loss of its mineral 
ingredients which the land sustains, is comprised 
in that portion which is sent into our large towns 
in the different grains and in the bones of ani- 
mals, and that other small (but unfortunately 
often too considerable) portion which is lost by 
the drainage of liquid from the stables and ma- 
nure heap. The purchase of bones to restore 
the phosphate of lime removed by the growing 
of sheep and the milk of the cows, should hard- 
ly perhaps be looked upon in the light of the 
application of artificial manures, because nothing 
can be more reasonable than to give back what 
we have taken from the soil; and the measures 
now in progress for rescuing the sewerage of our 
large towns, and an improved system in the ma- 
nufacture and preservation of natural manures 
at the homestead, will leave but little on the 
credit side of the land. But allowing a certain 
and considerable yearly diminution of the miner- 
al elements of fertility in land, we have yet, so to 
speak, an almost infinite supply of these bodies 
in the soil itself, provided we knew how we 
might economically avail ourselves of it, This 
(the item of expense) is after all, the turning 
point. Most soils, if sufficiently exposed by re- 
peated stirrings and cultivation to the action of 
the natural agents, water and air, would yield up 
abundant materials for the growth of luxuriant 
crops of roots, and through their means of corn. 
We know from the constitution of the rocks 
from which they have been produced, that all 
soils containing any clay, must contain also con- 
siderable quantities of potash ; and there is every 
reason to believe that no sandy or chalk soil is 
absolutely deficient in this alkali. Again, the ex- 
periments of Dr. Daubeny and Professor Fownes 
have led us to believe that phosphoric acid is 
a constituent of the chalk and limestone strata, 
as well as of the older rocks; and the recent in- 
vestigations of Dr. R. D. Thomson and of Mr. 
Sullivan, go a great way to prove that this acid, 
So important to agriculture, is present in all the 
great mineral masses of the globe, whether of 
ancient and igneous origin, such as granite, 
gneiss, and all volcanic rocks, or the more mo- 
dern aqueous deposits of which so large a portion 
of the soil of England consists. The presence of 
phosphoric acid in the older rocks however is the 
important point, because its existence (as inso- 
luble phosphate of lime) in the sedimentary de- 
Sr} 
VEGETABLE PHYSIOLOGY. | 565 
posits formed from the debris of the first, follows 
almost as a natural consequence. But though it 
is quite possible that, from the universal preva- 
lence of the most important mineral constituents 
of crops, sufficient working of the soil would 
enable us to dispense with the addition of any 
artificial manures, it may be, and is, far more 
economical at the present time to supply the 
requisite dose of mineral matter directly than 
to seek to furnish it from the natural resources 
of the soil by a costly expenditure of mechani- 
cal force. It must be observed, however, that 
there are other ways of bringing into play the 
dormant energies of the Jand, besides deep and 
subsoil ploughing and trenching. Some plants 
have an extraordinary capacity and disposition 
to seek food at great depths in the ‘soil—not ve- 
getable food, for there is none in such situa- 
tions, generally speaking, to be had, but mineral 
food. For this they will send down their roots, 
in many cases, to many times the depth which 
the most enthusiastic advocate of subsoiling 
would hope to attain; and in their subsequent 
growth at the expense of so distant a source of 
nourishment, they effect a far more important 
chemical addition to the surface soil than the 
subsoil plough could accomplish. The perfection 
of a fallow crop, either root or otherwise (other 
circumstances of facility of cultivation, amount 
and feeding properties of the crop being equal), 
would be that which, whilst requiring for the 
completion of its own structure a considerable 
quantity of valuable mineral ingredients, should 
be possessed of an energy and power of obtaining 
them quite independent of any extraneous sup- 
ply in the shape of artificial manures, 
words, a scientific review of the conditions of 
vegetable growth, apart from circumstances of 
practical detail, would indicate as the best fal- 
low crop a plant with large spreading leaves, 
strong penetrating roots, and nutritive qualities 
in the feeding of stock,-provided that at the same 
time its ash were in quantity and composition 
such as would benefit the cereals for which it is 
intended to prepare the food. Of. this latter 
point there would be little fear, supposing that 
the plant was really superior in feeding proper- 
ties; for an examination of the evidence at pre- 
sent existing in reference to the ash of plants, 
amply demonstrates that those parts of plants 
(such as the seeds of the cereals) which owe 
their high nutritive powers to the large quan- 
tity of nitrogenized bodies (gluten, albumen, &c.) 
they contain, are also proportionably rich—in- 
variably so—in phosphates of lime, magnesia, 
and potash. Let it not be thought from the 
foregoing remarks, that we can take only one 
narrow contracted view of the relation which 
the culture of the root crop bears to the whole 
rotation, or that we seek to explain the advan- 
tages of existing practices and modern improve- 
ments, solely upon chemical principles. A prac- 
tical farmer will tell us, that there are twenty 
In other 
