_ lutions, but indeed in many cases preferable. 
; 
Fuly x 
: oes 
0, 1873] 
larger spectroscope for the study of the pn amen of ca 
e de- 
scribes two different kinds of eye-piece, viz., a simple form 
made by Merz, and the far more complete Sorby- 
Browning, with the method of measurement proposed by 
Mr. Browning, and expresses his regret that the value of 
such instruments has been almost altogether overlooked 
by German botanists. In treating on the application of 
the apparatus, the author very justly points out the great 
advantage of having a bright illumination, without too 
much dispersion, and the importance of being able to 
examine the spectrum of a leaf or any other object in its 
natural state, in order to ascertain whether the colouring 
matters dissolved out from a plant by any solvent do 
really occur in it, or are products of decomposition. I 
would also myself add that in some cases the difference 
between the spectrum of a substance in a free state and 
when dissolved is so considerable that care must be taken 
not to conclude that there has been actual decom- 
position, until the character of the spectrum of the 
solid substance, in a free state, has been ascertained ; and 
even when the spectra are very nearly the same, the posi- 
tion of the absorption-bands may differ sufficiently to 
make it possible to determine whether a colouring-matter 
naturally exists in a free state or dissolved in water, or in 
an oil, according as it is or is not solubie in water. The 
fact of being thus dissolved or not is in some cases, pro- 
bably, a question of considerable physiological import- 
ance, since the existence of solid particles along with, or 
even actually surrounded by, a liquid capable of dissolv- 
ing them, points to a very different origin and relation to 
structure to those of a substance merely dissolved in the 
juices of a plant or an animal. The solution of such a 
colouring-matter is sometimes one of the first changes that 
occur in decomposition, as if set free from minute cells. 
Having explained the general methods employed, and 
given a list of the chief publications connected with the 
subject, the author proceeds to the consideration of 
various colouring-matters found in plants. If I had 
written this review immediately after the work was pub- 
lished, I should have expressed my agreement with the 
greater part of the author’s conclusions ; for they are 
those to which a most careful experimenter would be led 
by employing the methods generally known at that time ; 
but during the last year I have devoted myself exclu- 
sively to this particular subject and have been led to employ 
almost entirely new methods of investigation, and the result 
is that I must now point out a number of particulars in 
which J think the author’s conclusions are not altogether 
correct. These new methods consist chiefly in the more 
or less perfect separation of the different substances by 
means of bisulphide of carbon, alcohol, and water, used 
in varying proportions, and in a somewhat peculiar 
manner ; in the employment of what I have named fhozo- 
chemical analysis, or the use of light as a reagent, so as 
to destroy some constituents, and leave others, which per- 
haps could not be separated by chemical methods ; and 
in studying and comparing together all classes of plants, 
especially the lower cryptogamia, when growing in various 
conditiens ; and not only in examining them qualitatively 
but also in determining the relative amount of the different 
colouring-matters by a method of comparative quantita- 
tive analysis. I will not now enter into detail, but refer 
to a paper recently communicated to the Royal Society, 
on comparative vegetable chromatology, in which I have 
given a complete general description of the methods I 
have used, of the facts I have observed, and of the con- 
clusions drawn from them, which have a very direct bear- 
ing on some of the most important questions in biology, 
and enable us to examine them froma new point of 
view. 
One great value of the authors work consists in its 
giving a very complete account of the researches of pre- 
vious investigators, which I have myself found extremely 
NATURE 
203 
useful ; since so much that has been written is difficult of 
access. At the same time, since the methods employed 
were often altogether unsuitable, and most of the experi- 
ments are now known to have been made with mixtures, 
many of the results are of very little more than historical 
interest. The work also contains three excellent litho- 
graphed plates of the spectra of the various colouring- 
matters in @ natural or altered condition. ~The whole 
subject is treated in an admirable manner, and I trust 
that no one will think that I wish in any way to detract 
from the author’s merit in taking this opportunity to 
illustrate the application of the methods which I think 
should be employed in such researches. 
The coloured solutions obtained from leaves are very 
complicated mixtures. It is not at all unusual for them 
to contain as many as ten different coloured substances. 
The progress of our knowledge has to a great extent 
depended upon the application of improved methods, 
which have made it possible to distinguish the various 
constituents of these mixtures. The author has himself 
pointed this out, and shown that what was at one time 
called chlorophyll, and looked upon as a single substance, 
consists of a mixture of a bluer-green substance with a 
yellow substance. This kind of analysis had however 
previously been considerably extended. Ina very short 
paper,* containing no description of the methods of ex- 
periment, or of the separate colouring-matters, Stokes 
said that his researches had led him to conclude that the 
chlorophyll of land plants is a mixture of four sub- 
stances, two green and two yellow, and in my late paper 
I have shown that by the newer and improved methods 
it is easy to prove that there are not only these two green 
substances, one a blue-green and the other a yellow- 
green, having perfectly distinct and characteristic proper- 
ties, though confounded together by nearly all other 
experimenters, but also four or even five perfectly distinct 
yellow substances. These various colouring-matters I 
have named dlue chlorophyll, yellow chlorophyll, orange 
xanthophyll, xanthophyll, yellow xanthophyll, orange 
lichnoxanthine, and lichnoxanthine. They are all in- 
soluble in water, and soluble in bisulphide of carbon, and 
besides one or two products of decomposition, they must 
all have been present in what has sometimes been called 
chlorophyll, and looked upon as a single compound. 
Now, almost the only points in which I feel compelled to 
differ from the author are those cases in which the new 
methods of examination prove that what he regarded as 
a single colouring matter is in reality a mixture of two or 
even more, which can be separated, and do occur sepa- 
rately in particular plants. Thus, for example, in Plate II, 
Fig. 1, he gives a drawing of the spectrum of the blue- 
green colouring matter of Dewfzéa scabra, showing six 
absorption-bands. Now, I feel persuaded that this 
colouring-matter must have been a mixture of three 
different substances, viz. my blue chlorophyll, my yellow 
chlorophyll, and the product of the action of acids on 
blue chlorophyll The bands numbered 1, 2, 3, and 6 
are mainly due to blue chlorophyll. Part of No. 1 and 
No. 5 are due to yellow chlorophyll, and the band No. 4 
clearly indicates the presence of a small quantity of the 
product of the action of acids on blue chlorophyll. This 
is almost always present when the preparation is made 
in the manner adopted by the author, but by neutralising 
the acid of the juice by carbonate of ammonia, or still 
better by employing a plant that has an almost perfectly 
neutral juice, chlorophyll may be obtained which gives a 
spectrum almost absolutely free from any such band. 
In the spectrum shown by Plate III. Fig. 1 of the blue- 
green colouring-matter of an Osczl/atoria, the bands of 
yellow chlorophyll are absent, for it does not exist in such 
Alge, but the broad band shown at about 500 of the 
author’s scale, not seen in the spectrum of the chlorophyll 
of Deutzia, must have been mainly due to orange xantho- 
* Proceedings of the Royal Society, 1864, xiii. p. 44. 
