228 
INVESTIGATION OF SOILS. 
in water. Now, heath-mould contains little else than sand and vegetable matter 
reduced from the plants which itself produces ; and therefore leaf-mould becomes 
inappropriate to the heath-tribes, which cannot generally flourish in richer soils. 
In analysing heath and leaf-moulds, the latter will be found far the more 
complicated, but both are richer in humie substances than loams ; while the 
inorganic constituents of the latter, existing in the ashes after ignition, are very 
different from the simple white sand of the former ; and this circumstance, when 
fairly proved by experiment, will satisfy the inquiring gardener that he cannot in 
all cases substitute the one for the other ; though practice will clearly point out 
which of the two must be applicable to individual plants. 
There is one substance that cannot be deemed either earth or manure, but 
which offers many advantages to pot-culture, and now begins to be appreciated. 
Charcoal is this substance : it is quite insoluble ; it changes not, and is not liable 
to decay or putrefactive fermentation ; but it absorbs ammoniacal and other gases 
to the extent of many times its own bulk, becomes also saturated with water, and 
retains moisture pertinaciously ; hence, it forms the best sort of drainage, supplying 
the root with aqueous and gaseous matter/ suitable to their habits, yet never 
producing change or decay. It is at once the most innocuous and useful of 
negative appliances, and may doubtless be added to soils in small fragments, as a 
preventive of aridity. 
It is decomposed by ignition, and then is converted into carbonic acid gas ; 
this gas is also developed constantly during the slow decay of vegetable remains, 
and thus becomes a fertile source of nutriment to the roots, and perhaps to the 
whole plant through the pores of the leaves. 
From what has been stated, we hope that some idea will be formed of the 
compound nature of soils, and of the necessity which exists for the rigid investi- 
gation of every species of plant in order to obtain correct views of cultivation. 
It is now known, that, besides the earthy matters, soils contain four, if not 
five species of vegetable organic substances soluble in water, and the three alkalies ; 
these are with certainty derived naturally from vegetable decaying matter, though 
in varying quantities ; they are termed by chemists, crenic, and apocrenic, humic, 
geic, and ulmic acids : but if there be a deficiency of inorganic elements, the 
material wanting must be confined by art, otherwise a plant which requires chalk, 
cannot thrive in earth destitute of or ill-supplied with that earth ; another which 
thrives in soil containing phosphate of lime or soda will languish under opposite 
circumstances. 
These facts are decisive of the utility of chemical appliances, and they also 
account for the constant complaint which we hear of loam, and of the difficulty 
which one gardener meets with in cultivating some tribes that his neighbour or 
acquaintance raises in luxuriant perfection ; there are causes for all things, and 
some of these chemistry has discovered, and continues still to discover. 
We dwell more particularly upon the necessity of unremitting, strict researches, 
