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Mr. H. C. Sorby on 



[June 19, 



those two kinds of xanthophyll, and it resists the action of light far 

 more than they do. A mixture of pure orange xanthophyll and xantho- 

 phyll in absolute alcohol treated with hydrochloric acid would, at the 

 most, give only a pale green, whereas fucoxanthine is changed into a 

 splendid blue substance, and subsequently into a sort of claret-coloured, 

 before finally and slowly fading. Though the spectra of fucoxanthine 

 and } r ellow xanthophyll are essentially different, yet this blue product is 

 the same. It absorbs the whole of the red end of the spectrum, not 

 transmitting even the extreme red ; and on adding an excess of ammonia 

 this absorption is entirel} 7 " removed, and the colour is changed to a bright 

 yellow. The spectrum then shows a well-marked absorption-band at the 

 violet end of the blue. On adding excess of hydrochloric acid, the ori- 

 ginal blue colour is restored ; and hence this substance has the unusual 

 peculiarity of being made blue by acids and yellow by alkalies. Hitherto 

 I have never met with it in plants themselves. Taking every thing into 

 consideration, we must look upon fucoxanthine as closely related to 

 xanthophyll ; but at the same time the different effect of solvents in 

 raising the absorption-bands, and the greater permanence when exposed 

 to light, may perhaps make it desirable to class it in a subgroup. The 

 dull olive colour of those Algce in which it occurs so abundantly (the 

 Melanospermw) is apparently mainly due to it in a free state, not dissolved 

 in any oil. On comparing the spectrum of the light transmitted by a 

 frond in its natural condition with that of the light transmitted by a 

 portion which has been boiled for a short time in water until the colour 

 has changed to green, it may be seen that the absorption due to the 

 fucoxanthine is considerably raised, just as if at that high temperature 

 it were attacked and dissolved by the oil present in the plant. 



Lichnoxanthine Group. 

 This is a name which I propose for a number of colouring-matters 

 found in a great variety of plants. Two are more especially abundant 

 in fungi ; but since they occur in a more marked manner in lichens 

 than in any other plants having true leaves or fronds, it appears to me 

 desirable to adopt the name lichnoxanthine rather than fungoxanthine, 

 which perhaps may be found convenient for some of the substances found 

 more especially in fungi. So far I have met with three different kinds 

 of lichnoxanthine in the leaves and fronds of plants. They are all in- 

 soluble in water, and soluble in bisulphide of carbon, but have a far 

 greater tendency to dissolve in alcohol ; and in some cases easily pass 

 into a modification which is insoluble in the bisulphide, and yet readily 

 dissolved by absolute alcohol. The spectra do not show any well-marked 

 absorption-bands, but merely a general absorption, extending more or less 

 from the blue end, according to the particular species, and very little if 

 at all modified by the addition of weak alkalies or acids. All are of a 

 much more permanent character than the different kinds of xanthophyll, 



