1“ 
NATO RE 
THURSDAY, AUGUST 31, 1871 


ON THE VARIOUS TINTS OF FOLIAGE 
Pear wees we cannot yet say— 
Far, far o’er hill and dale green woods are changing, 
Autumn her many hues slowly arranging, 
still it may be interesting to put together certain facts 
with reference to the tints of foliage which have recently 
been acquired to science. 
Up to the present time I have been able to distin- 
guish several dozen colouring matters in the leaves of 
different plants, and far more in the petals and fruits, and 
no doubt further inquiry will very greatly increase this 
number. The subject would, therefore, be quite un- 
manageable, if we could not divide them into well-marked 
groups by means of their optical characters. This is still 
more important when, as on the present occasion, it is 
desirable to give a condensed summary of the leading 
facts. I shall, therefore, not attempt to describe the in- 
dividual colouring matters, or to explain how they may be 
distinguished or identified by means of their spectra, either 
in their natural state or after being acted on by re-agents; 
but merely point out the general relations of the various 
groups, and refer to my published papers for illustrations 
of the methods employed in the inquiry.* The colours 
of these groups are not only related to one another opti- 
cally and chemically, but also have a very similar connec- 
tion with the growth of the plants, and thus it is possible 
to give a general explanation of the very various tints of 
foliage, without entering into technical details. Foramore 
complete account, I beg to refer to a paper on this subject, 
just published in the July number of the Quarterly 
Fournal of Microscopical Science. 
One of the chief difficulties in studying the colours met 
with in plants is, that they are often mixtures of quite 
distinct colouring matters. Sometimes these may be easily 
separated, for one may be soluble, and the other insoluble, 
in such reagents as water, alcohol, ether, or bisulphide of 
carbon; but in many cases they are so closely related, 
that anything like a complete separation is perhaps im- 
possible ; even then, however, it may be possible so to effect 
a partial separation, that the presence of two different sub- 
stances may be recognised, and with proper care a very 
good opinion may be formed as to their general properties. 
Nature, also, herself often assists us in this inquiry, for 
different plants, or the same in different states, may furnish 
particular colouring matters comparatively pure, or so 
variably mixed that the character of the mixture may be 
recognised. 
For the purposes of the subject before us, I have found 
it desirable to divide the different colouring matters into 
the following groups :— 
1. The Chlorophyll group is distinguished by being in- 
soluble in water, but soluble in alcohol and in bisulphide 
of carbon, There are three or tour species, giving well- 
marked spectra, with several narrow, dark, absorption- 
.* Proceedings of the Royal Society, vol. xv., p. 433 (Philosophical Maga- 
sine, vol. xxxiv., 1867, p. 144); Quarterly Fournal of Microscopical Sx tence, 
vol. ix., 1869, pp. 43 and 358; Monthly Microscopical Fournal, vol. iii., 
1870, p. 229 ; Quarterly Fournal of Science, new ser., vol. i., 1870, p. 64. 
VOL, IV. 
341 

bands, one or more of ;which occur at the red end. The 
mixed chlorophyll of ordinary green leaves may be ob- 
tained in a tolerably satisfactory state by heating in 
alcohol dark green holly leaves, previously crushed so as 
to insure rapid solution, and then, when cold, agitating in 
a test tube with bisulphide of carbon. This sinks to the 
bottom, holding nearly the whole of the dark green chlo- 
rophyll in solution, whilst nearly all the xanthophyll 
remains dissolved in the alcohol. Leaves having an acid 
juice must not be used, for that would change the normal 
chlorophyll into another modification, nor should the 
solution be left long in contact with them, for then the 
separation is much less perfect. 
2. The Xanthophyll group also contains several distinct 
species, but only two are common in leaves, one being 
more, and the other less, orange. They are characterised 
by being insoluble in water, but soluble in alcohol and 
in bisulphide of carbon; and when dissolved in this latter 
their spectra show two not very distinct absorption-bands 
at the blue end; but the red, yellow, and yellow-green 
rays are freely transmitted. They may be obtained from 
yellow leaves, by the use of alcohol and bisulphide of 
carbon. 
3. The Evythrophyll group comprises a number of 
colours soluble in water, in alcohol, and in ether, but in- 
soluble in bisulphide of carbon. Those met with in leaves 
are more or less purple, made bluer by alkalis, and redder 
by acids ; and thus sometimes plants containing the same 
kind may vary more in tint, owing to a variation in the 
amount of free acid, than others coloured by entirely dif- 
ferent kinds. The erythrophyll may be obtained, free 
from chlorophyll and xanthophyll, by heating the leaves 
in alcohol, evaporating to dryness, redissolving in water, 
filtering, and evaporating at a gentle heat; but, on the 
whole, it is better to digest the leaves for a day or so in 
sufficient cold ether to dissolve all the contained water, 
and then to agitate with water, which subsides to the 
bottom, with nearly all the erythrophyll in solution, but 
mixed with more or less of the colours of the following 
group. There are many species of erythrophyll, some of 
which have very interesting botanical relationships, being 
so far found only in particular classes of plants. 
4. The Chrysotannin group contains a considerable 
number of yellow colours, some so pale as to be nearly 
colourless, and others of a fine, dark, golden yellow. 
They are soluble in water, in alcohol, and in ether, but 
not in bisulphide of carbon, Their spectra show a 
variable amount of absorption at the blue end, usually 
with no bands when in their natural state, but sometimes 
with one or more sufficiently distinct when they are 
oxidised. They may be obtained free from chlorophyll 
and xanthophyll by processes similar to those made use 
of in the case of erythrophyll, and leaves should always 
be selected which are as free as possible from colours of 
that group. Some of the chrysotannin colours strike a 
dark colour with ferric salts, and constitute the tannic acid 
sub-group, of which there are at least six different kinds, 
whereas others do not give any such reaction, and consti- 
tute the chrysophyll sub-group. In both sub-groups the 
intensity of colour is usually greatly increased by partial 
oxidisation, and they are thus altered into colours of the 
following group. 
5. The Phatophyll group comprises a number of more 
i 
