CHAP. XIV. 
COLOUR AND SMELL. 
363 
without the flowers losing much colour. Acids produce no 
other effect in these infusions than to weaken their colour 
slightly. Alkalis make them more brilliant or browner. 
" Blue flowers produce, in alcohol, infusions either of a 
clear blue, as those of flax ; or very dark, as in the case of the 
aconite and the larkspur. By the addition of acids they 
become red, and of alkalies green. Those which are coloured 
red by acids will not recover their blueness by the addition 
of alkalies, as sometimes happens to infusions of red flowers. 
Macaire having seen a red infusion of violets regain by de- 
grees the natural blue of those flowers, by the addition of a 
vegetable alkali, such as quinine or strychnine, suspects that 
the colour of the violet depends upon the combination of 
their chromule with some alkali. Schubler and Funk assure 
us that the infusion of the blue day lily (Funkia coerulea), 
treated with an acid, will present in the same glass all the 
tints of the coloured spectrum. Blues are among the most 
changeable colours in vegetation, passing freely to white, and 
to different tints of violet and red. 
" From what has now been stated, it appears to result that 
modifications of chromule are the cause of the diversity of 
colours ; and that these modifications depend principally upon 
the degree of oxygenation. In leaves fully developed the 
chromule is green ; it gains a tendency to yellow or red when 
it is more oxydized, as one perceives by the changes of the 
colour of leaves in autumn by the effect of acids ; and it ap- 
pears to verge to blue when it is less oxydized, or, which 
comes to the same thing, more carbonated : thus we know 
that the flower of the Hydrangea becomes blue in a soil suf- 
ficiently impregnated with carbonate of iron. 
" All the brilliant spectacle of vegetable colours tends to 
disappear either in consequence of accidents or upon the ap- 
proach of death; and what renders this subject the more 
cvu'ious is that, 1. discolouration is often determined by the 
same agents as in other cases produce colour ; and 2. that 
certain organs which have no colour while alive gain when 
dead a very decided tint. 
" Solar light seems to be the most usual cause of those 
losses or changes of colours. While plants are alive, it acts, as 
