CHAP. XIV. 
COLOUR AND SMELL. 
365 
have them present for our use; but as to the reasons why 
one kind of flower is odoriferous, and another scentless, we 
are still more in the dark than in what relates to colour. 
Here, therefore, we shall confine ourselves very much to a 
mere statement of facts, introducing theory only in cases 
which may appear to be pretty well understood. For this 
purpose we again avail ourselves of many of the materials 
collected by De Candolle in his invaluable Vegetable Physio- 
logy, 
" All odours are owing to the disengagement of volatile 
matter ; and as there are few organized bodies in which, in 
their natural state, there is not some volatile constituent part, 
so neither are there many organic bodies absolutely destitute 
of smell. But it is only to cases in which the scent is very 
perceptible to our senses that we apply the idea of odoriferous, 
and it is consequently to those that we here confine ourselves ; 
dividing them into permanent, fugitive, and intermittent, 
" Those odours are the most permanent in which the volatile 
matter is so inclosed in cells and concentrated as to disperse 
slowly. Of this many instances are afforded by wood and 
bark, which being in truth the only permament parts of 
vegetation, will of necessity be the receptacle of durable 
odours ; such parts are not scented, because of their own 
proper nature, for all the tissue of plants is originally scent- 
less, or nearly so ; but they owe their property to the fragrant 
secretions imprisoned in their cavities, and the permanence of 
their odour will be proportioned to the difficulty the volatile 
parts of their secretions experience in escaping through the 
tissue which incloses them, as well as to the degree in which 
the volatile matter may be fixed. Thus resinous woods, such 
as cedar and cypress, are fragrant for an indefinite period, 
because the resinous matter in which their odour resides is 
parted with slowly. Parts, whose scent resides in essential 
oil, preserve their scent for a long time, where the essential 
oil is but slightly volatile, or the wood is thick and hard : 
thus the rose- wood of Teneriffe (not the rose- wood of the 
English cabinet-makers), produced by Convolvulus scoparius, 
preserves its odour a very long time ; and in order to elicit it. 
