compound constituents of vegetables. It not only forms almost 
the whole of the bulk of the trunks and boughs of trees, and shells 
of fruits ; but it also forms a great part of the husks, and lanugi- 
nous coverings of seeds, as well as of the epidermis of leaves, &c. 
The quantity in which it exists agrees therefore in the abundance 
of bitumen which seems to be yielded by that species of fermen- 
tation to which I have presumed that vegetables are subject ; and 
it is also worthy of notice, that the substances, which have been 
just described, as containing a predominating proportion of the 
ligneous part, are those substances which are most frequently found 
in a bituminous or in a mineral state. 
The contemplation of nature teaches, that there exists a regular 
system of dissolution and renovation, through all her works ; and 
that there are certain laws, according to which, substances are forced 
to quit one form of existence, and take on another ; their principles 
entering into new combinations, and forming other substances equally 
necessary in the economy of nature. Thus is constituted the never- 
ending chain of varying existences, in which, though each link 
differs from the rest, yet such is their symmetry and proportion, 
that they form a whole, in which beauty and utility are eminently 
conspicuous. But when we view the chemical history of the ig- 
neous matter of vegetables, a link appears to be lost, and the chain 
broken ; for whilst other substances yield either to the vinous or 
to putrid fermentation, the ligneous, we are told, seems to resist a 
nature’s efforts to force it into a new mode of existence. So re- 
fractory does it appear, that it is esteemed the most insoluble and 
unchangeable of all vegetable substances. If wood be exposed m 
a close vessel to the destructive action of fire, so little of the lig- 
neous substance is lost, that a charcoal is left which still retains 
the form of the piece of wood it originally composed. is ex 
periment serves also to show that the ligneous substance con ai 
the greatest quantity of carbon of any vegetable substance , an 
