— Fuly 17, 1873) 
and the mixture would also turn blue, but of only about 
5 owes 4a 
NATURE 
225 
half the depth of colour. If lichnoxanthine had been 
present it would have caused the colour to be green ; and, 
after the blue product had faded, it would remain as a 
residual yellow. By experimenting with such known 
mixtures we therefore see that, independently of being 
able to partially separate the constituents, the evidence of 
the solution being a mixture consists in the difference in 
the position of the absorption-bands, in the change in 
their position, or disappearance, when partially decom- 
posed by light, and in the relative quantity of blue 
substance formed by the action of hydrochloric acid, and 
of the residual yellow. Such, then, being the case, we 
know what kind of methods to employ in studying 
natural coloured solutions, suspected to be mixtures ; and 
on applying them to the investigation of the solutions ob- 
tained from leaves and flowers, 1 find that they behave 
exactly like such artificial mixtures, and not only so, but 
there is generally no difficulty in more or less perfectly 
separating the constituents, so as to correspond more or 
less closely with the different substances in their more 
pure state. The evidence of their being mixtures is there- 
fore as good as could be expected. Kraus seems 
never to have made such experiments, and yet he strongly 
criticises what I had said about the existence of several 
distinct kinds of xanthophyll; but y eontend that by 
adopting the principles I have described, we can com- 
pletely explain the various facts on perfectly simple 
principles, without suppoging that the optical characters 
of any single substance are subject ta variations from 
some unknown, and, as J believe, altogether ymaginary 
cause, : 
The igwers of different varieties of Euychscholtsia cali- 
Sornica A g@ a good illustration of my yiews. The 
very yellow fe g are coloured by yellow xanthaphyll 
with a very little xanthophyll and lichnoxanthing, and 
thus correspond with many other similar flowers, 
but the more orange-coloured petals, and the ‘orange- 
coloured portions of the yellower petals, contaig in add 
tion, another colouring-matter, giving the absorpfion-band 
in the green shown in Plate I. Fig. 7,at 1 a, of Kraus's work 
which, howeyer, he did not look upon as eyidence af a 
mixture—merely of what he calls a radifvation, Now, 
on exposing such a sqlution in bisulphide of carbon ie the 
sun, this erange-caloured sybstance is more yapidly de- 
composed than the others, and in a while a yellower 
solution is left, which gives exactly ie same spectrum 
as that due ta the coloyring-matter fram the ella petals, 
According to this view ef the subject we therefore sce 
that the yellaw flawers are of the usnal type, and that 
the more orange-coloured portions of the petals, and the 
whole of the orange-coloured varieties differ only in there 
being developed an unusual and independent substance, 
which in this case is of orange-colour, whereas in the 
flowers of some other plants, such additional colouring- 
matters are red or blue, as the case may be, and instead of 
being allied to xanthophyll, differ in almost every particular. 
In conclusion I would say that the yellow colouring- 
matters, soluble in bisulphide of carbon, which exist in 
green leaves, are the above-named xanthophyll, yellow 
xanthophyll, and lichnoxanthine. This is probably the 
reason why this is also the normal type of yellow flowers, 
and why only in particular cases one or both of these sub- 
stances are absent. To this I attribute the statement of 
the author that the chemical reactions are the same, for 
he has apparently never examined those plants which 
yield them in an approximately pure state, 
In Pl. Ill. Fig. 2, Kraus gives a representation of 
the spectrum of a coloured solution obtained from 
certain species of Oscéllaforiz. This he has named 
phycoxanthine ; but I am persuaded that the solution 
must have contained three perfectly distinct colouring- 
matters, which can be separated by chemical and 
photo-chemical methods, and do occur almost, or 
a: 
quite, separately in other plants, For one of these 
substances I have adopted the author's name phyco- 
xanthine. It may be obtained in the most pure state 
from the lichen Peltigera canina, when growing in 
such a damp and shady situation, that very little orange 
lichnoxanthine is developed. When dissolved in absolute 
alcohol and hydrochloric acid is added, it fades 
without turning blue. Another constituent of the mixture 
is what I have called /ucoxanthine, which occurs quite 
free from phycoxanthine in Fucus and other olive Alge, 
and even in the same species of Oscillatoriz, growing 
where there is very little light, as those which 
contain phycoxanthine, if growing well exposed to 
the sun. When dissolved in absolute alcohol and 
hydrochloric acid is added, it turns to a splendid 
blue. The third constituent of the mixed solution 
is what I have named orange Jichnoxanthine, which can 
be obtained by itself from lichens, and is left when such 
a mixed solution as described by the author, in bisulphide 
of carbon, is exposed to the sun under green glass, until 
the phycoxanthine and fucoxanthine have been destroyed. 
When dissolved in absolute alcohol and treated with 
hydrochloric acid it fades very slowly. The relative 
amount of this is greatest in those specimens of Osci//a- 
torie which grow very much exposed to the sun and air, 
and I have found by careful comparative quantitative 
analyses that the relative quantity of these various sub- 
stances, which together constituted the author’s phyco- 
xanthine, varies in such a manner that, as far as the 
fundamental colouring-matters are concerned, the same 
or closely allied species of Oscétlatorie, growing exposed 
to a varying amount of light, furnish.a most interesting 
series of connecting links between olive 4/g@and lichens, 
When their vitality and constructive energy are very 
much reduced by want of light, their type a colouring 
clasely approaches to that of olive Alg@, whereas when 
they are exposed to much gir and light, the type ap- 
proaches to that of such lichens as Pa wera canina, 1 
have met with other analogous cases, and if more ex- 
tended research should still further confirm the existence 
ort is analogy between the results due to abnormaliy 
reduced or increased vitality in the same kind of plants, 
and the normal characters cf lower and higher classes of 
plants it would certainly be remarkable, as showing that 
he vegetative energy of the lower classes is in some way 
or other of a lawer type than that of the higher classes, 
and would present @ striking analogy to the relation 
between the structure ef animals whose deyelapment has 
been arrested and that af those of lower grganisation. 
The fact being able to prove that a coloured solution 
obtained from a plant is really a mixture of a number of 
different substances, may at first sight appear to be of 
very little consequence, but I trust that some of the con- 
clusions deduced from this method of study will justify 
me in looking upon it as very well worthy of attention. 
When we come to study the various classes of plants 
growing under various conditions, with the view of con- 
structing such a general science as that I have named 
comparative vegetable chromatology, these details become 
not only of the very greatest importance, but absolutely 
essential. By making qualitative and comparative quan- 
titative analyses of the colouring-matters, carefully dis- 
tinguishing the fundamental from the accidental, there 
seems every reason to believe that the petals and the 
foliage of plants can be brought into morphological 
agreement, and many of the leading classes of plants 
distinguished, and at the same time connected together, 
so as to form a continuous series, advancing from the 
lowest classes cf animals to the highest classes of plants ;. 
whereas, if we were to look upon mixtures as independent 
colouring-matters, and were not to distinguish well-marked 
species, the whole vegetable kingdom would appear 
broken up and disjointed, without any chromatological 
continuity, H.C. Sorby 
