766 
GENERAL CONDITIONS OF PLANT-LIFE. 
must have been due to a mixture of the latter two. Olive Algae contain another 
fundamental species, fucoxanthine. In many Fungi, and in the petals of flowers, occur 
other more orange-coloured species, of which that in Pe%i%a aurantiaca is a good 
example. Sorby adopted the name proposed by Kraus^ for a still more red orange- 
coloured species ; but M'hat Kraus describes as phycoxanthlne must have been a mixture 
of this substance with fucoxanthine and lichnoxanthine. The difference between the 
spectra of some of the above-named species will be better understood by means of the 
following figure (476 r), which represents those of the solutions in carbon bisulphide. 
When these various substances are dissolved in benzol, their absorption-bands are all 
equally raised towards the blue end, so that w^e appear to have a remarkable series of 
very closely related substances. 
Lichnoxanthine group. — The colouring-matters belonging to this division are insoluble 
in water, soluble in absolute alcohol, and sometimes also in carbon bisulphide. They all 
give spectra without bands, and absorb more or less from the blue end. Some are 
yellow, and others so red that they may be called Hchnoerythrines. Lichnoxanthine 
Red 
Phycoxanthlne 
Peziza xanthine 
Orange xanthophyll . . 
Xanthophyll 
Yellow xanthophyll . . 
Fig. 476 c-.— Spectra of the xanthophyll group compared. 
occurs in both the highest and lowest classes of plants, but the whole group is more 
especially developed in Lichens and Fungi. It is not yet possible to say what part they 
play in the economy of plants, and in some cases they are probably only products of the 
oxidisation of chlorophyll and resins, from which they may be prepared artificially. 
We now come to a number of different groups, soluble in water but insoluble in 
carbon bisulphide. 
Phycocyan and Phycoerythrine groups. — There are at least five distinct colouring- 
matters included in these two groups, which differ from one another in many well-marked 
particulars. The phycocyans are highly fluorescent, but the phycoerythrines little if at 
all. They give remarkable spectra with one main absorption-band. Some are con- 
nected with albuminous substances in much the same manner as the hsemoglobin of 
blood, being like it decomposed at exactly the same temperature as that at which 
albumen coagulates, whilst the others appear to be associated with some different but 
related substance. They are especially characteristic of red Algae, but also occur in a 
few Lichens. 
* Chloiophyllfarbstoffe, p. 109. 
