GENERAL CONDITIONS OF PLANT-LIFJß. 
distinct colouring matters by a simple dialytic process. Conrad has shown, howe^-er 
(Flora, 1872, p. 396), that if a solution of chlorophyll in absolute alcohol be treated with 
benzol, a separation of the green and the yellow never occurs. This only takes place 
when dilute alcohol, of a strength less than 65 per cent., is used. Conrad points out 
forcibly that Kraus used dilute alcohol, which may be at once inferred from the fact 
that he extracted the boiled leaves with alcohol without having previously dried them. 
According to Conrad, it is very doubtful if this decomposition of the chlorophyll is 
simply a dialytic phenomenon. More probably a decomposition had previously been 
effected by the water, a suggestion which is supported by the fact that solutions of 
chlorophyll in dilute and in absolute alcohol when evaporated give in the former case, 
but not in the latter, a residue containing a yellow colouring-matter soluble in water ^. 
The yellow colouring matter is soluble in alcohol, ether, and chloroform, but not 
• in water. On addition of hydrochloric or sulphuric acid (as Micheli had already shown) 
it becomes first emerald-green, then verdigris-green, and finally indigo-blue; the 
spectrum of the yellow substance which has in this manner become green shows al- 
together different absorption-phenomena to those of chlorophyll. The spectrum of the 
yellow ingredient of chlorophyll is identical (Kraus) with that of most yellow flowers (as 
, Ranimculus, Mimu/us, Gentiana lutea, Brassica, Taraxacum, Matricaria, &c.), and agrees 
with it also in the reactions just named, as also does that of the yellow colouring 
substance of fruits and seeds {Euonymiis, Solanum Pseudocapsicum, Slc). This yellow 
substance is, like chlorophyll, combined with protoplasm. The substance present in 
the cells in the liquid form, as for instance in the flowers of the Dahlia, is diff^erent ; 
it is soluble in water, and does not give a spectrum consisting of bands, but a continuous 
absorption of the blue and the violet. The colouring substance of some orange flowers, 
e.g. Eschs cholt%ia, also soluble in alcohol, is again different, possessing a fourth band in 
the blue-green to the left of the three bands of the ordinary yellow substance. The 
colouring matters of bright-coloured lower organisms which are soluble in alcohol are 
not identical with either of the two which constitute chlorophyll, but are related to them. 
According to Kraus, the yellow substance of etiolated leaves also exactly resembles 
the yellow constituent of chlorophyll. 
The Fluorescence of the colouring-matter of chlorophyll is seen from the fact that 
a sufficiently dark concentrated solution appears dark-red by reflected but green by 
transmitted light. The fluorescence is much more decided if the pencil of converging 
rays of the sun is made to fall on the green fluid through a condensing lens. If the 
solar spectrum is thrown upon the surface of a solution of chlorophyll^, it may be 
ascertained which rays of the sunlight cause the fluorescence ; the red begins a little 
to the left of the line B of the solar spectrum, and stretches, although varying in inten- 
sity, over the violet end. On the dark-red ground are seen seven intensely red bands, 
each corresponding exactly both in position and in strength to an absorption-band 
, in the spectrum of chlorophyll. If the fluorescence caused by the solution of chloro- 
phyll is itself observed through a prism, it is seen to consist only of red rays, the 
refrangibility of which coincides with the strongest absorption-band of chlorophyll 
between B and C. Every ray produces by fluorescence only such as correspond in 
their refrangibility to the absorption-band /. Whether the chlorophyll contained in 
living cells is subject to the same fluorescence is not certain, from the imperfect 
^ [Pringsheim (Ueb. d. Asorptionsspectra der Chlorophyllfarbstoffe, Monatsber. d. k. Akad. d. 
Wiss. zu Berlin, 1874) confirms Conrad's observations. He shows that the separation into two 
layers depends upon the fact that benzol will not mix with weak alcohol, but will do so with strong. 
He also points out that under any circumstances some of the benzol is retained in solution in the 
alcohol, and further that benzol will dissolve more chlorophyll than alcohol and will therefore 
become more deeply coloured. He maintains that the yellow colour of the alcohol is due to the 
presence of some chlorophyll in it, as shown by the spectroscope, though some yellow colouring- 
matter (etiolin or xanthophyll) is also present.] , 
^ Halenbach, Pogg. Ann, vol. 141. p. 245; Lommel, ih. vol. 143. p, 572, 
