760 GENERAL CONDITIONS OF PLANT-LIFE, 



distinct colouring matters by a simple dialytic process. Conrad has shown, however 

 (P^lora, 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 

 Ranunculus, Mimulus, 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 {Euonymus, Solanum Pseudccapsicum, &c.). 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 different ; 

 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. Eschscholtzia, 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. 

 Wis?, 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.] 



^ Hagenbach, Pogg. Ann. vol. 141. p. 245 ; Lommel, ih. vol. 143. p. 572. 



