GARDENING AS A SCIENCE. 
59 
components — namely, alumina, chalk, oxide of iron, and particularly the sileo) or 
sand ; which, in proportion as it is fine and silky, or coarse and gravelly, constitutes 
the unctuous, or gritty loam. 
When we admit, and which in candour we must, that no one can command 
the staple soil employed by another in a distant locality, surprise at failures or 
perplexity must cease ; and we can have recourse only to the best and most apt 
modifier of the discrepancies of loams. This will be generally found in the thinly 
pared turf of a field or common, not manured by art. Such turf the late Mr. 
Knight would have used, green, and chopped fine by the spade ; but most persons 
will prefer to let it mellow and decay in a heap during one summer and one 
winter, during which period it is to be turned and wrought with the spade, twice 
or thrice. But herein we must guard against a common error. Turf is a 
substance replete with vegetable matter— a species of manure — the elements into 
which it is resolvable being carbon, oxygen, and hydrogen — or, in other words, 
those of woody fibre and of water. 
Now, in process of time, this vegetable manure is dispersed into the air ; or, 
if under culture, is taken up by the absorbent power of the growling plants, leaving 
the base or loam unaltered in any degree, excepting the abstraction of its soluble 
potash or soda, and a slight portion of chalk. 
Loam^ therefore, must be viewed as a combination of metallic earths, in a form 
most efficient and sta])le for all the purposes of agriculture, and the production of 
nutritious garden vegetables ; it retains these earths consistently, but parts with its 
salts : it also retains manuring substances with a degree of pertinacity varying in 
conformity to its texture, and the proportion of its alkalies. But as its own base 
cannot be decomposed by vegetable action, it becomes poor (exhausted) by the 
dispersion or total decomposition of the manure introduced by man. 
This assertion must, however, be qualified to a certain extent ; because chalk, 
one of the components of loam, is slightly soluble in water itself, and considerably 
so when it meets with some acids. Chalk is found abundantly in the ashes of 
many plants, and in those of all timber-trees that we have examined ; but no one 
could detect a trace of it in the sap or juices of a living vegetable. It must 
therefore be admitted that a portion of it is dissolved, and thus attracted by the 
plant, in the organs of which it combines with some organic acid, and forms a 
neutral salt or compound of lime, which the action of fire decomposes, destroying 
the acid, and leaving the lime in the condition of a carbonate. 
As an exemplification — Tobacco, cultivated in the garden, (or the Potato plant, 
which is related to it, botanically,) does not exhibit a trace of chalk ; but let it be 
dried, and burned in an earthenware vessel, and the white ashes will effervesce 
strongly, if vinegar, lemon-juice, or spirits of salt be poured on them. This hissing- 
will, it is true, partly depend upon the potash, which also exists in the ashes ; but 
the presence of chalk may be ascertained by dropping a small quantity of dissolved 
salt of tartar into a solution made, by treating the ashes with the acid last named, 
