CHAP. XIV. COLOUR AND SMELL. 359 
same chemical characters as that of leaves which turn red 
in autumn. Such bracts appear coloured because the chro- 
mule deposited in their cells varies in its degree of oxygen- 
ation, and such variations appear to be in distinct relation 
with the flowers. The same observations apply to many 
calyxes. 
" Why then should it be different with petals and the 
petal-like parts of a flower? These organs are in truth 
nothing but modified leaves ; they are capable in particular 
cases, such as Hesperis matronalis, of transforming them- 
selves into genuine leaves, green, and capable of exhaling 
oxygen. Can there be any the smallest reasonable doubt 
that these leafy petals contain in their cellules a chromule 
analogous to that of leaves, and consequently that when 
they are coloured they owe their colouring to a modification 
of chromule ? 
" It is therefore probable that all the various colours of 
flowers, with the exception of certain special cases determined 
by the presence of some free alkali or acid, depend in gene- 
ral upon the various degrees of oxygenation of their chromule : 
and that this theory ought to extend to fruits and bracts 
where those organs participate in the same colours. 
" With regard to the exact relation that colours really bear 
to one another, and to the causes that are supposed to influ- 
ence them, a memoir upon the colours of flowers, published 
at Tubingen, in 1825, by Messrs. Schubler and Funk, is 
deserving of especial attention. From their account it ap- 
pears that flowers may be divided into two great series — 
those having yellow for their type, and which are capable of 
passing into red or white, but never into blue ; and those of 
which blue is the type, which can pass into red or white, but 
never yellow. The first of these series is called by these 
observers oxydized, and the second disoxydized, and they 
consider greenness as a state of equilibrium between the two 
series. De Candolle calls the first series xanthic, and the 
last cyanic. Upon this principle they admit the following 
scale, leaving white out of consideration : — 
A A 4 
