80 SUMMARY OF CURRENT RESEARCHES RELATING TO 



hitherto recognized only in the fruit of the tomato and the root of the 

 carrot, they occur in a large number of fruits, seeds, and even flowers. 

 All the coloured substances arise in the peripheral zone of chloroleucites 

 or of uncoloured leucites. 



Yellow pigments are always amorphous, and incapable of artificial 

 crystallization ; they are but slightly soluble in chloroform, ether, or 

 benzin, much more so in alcohol, insoluble in water. The residue left 

 on evaporating an alcoholic solution, when treated with concentrated 

 sulphuric acid, is coloured, like the solution itself, at first green, after- 

 wards blue. It may be called xanthin. Orange-red and orange-yellow 

 pigments are insoluble in water, soluble in alcohol, but more so in ether, 

 chloroform, and benzin. They are either amorphous or crystalline, or 

 intermediate between the two conditions. Treated with concentrated 

 sulphuric acid, they are all coloured violet or violet-red, afterwards 

 indigo-blue. The gooseberry-red pigment is peculiar to the flowers of 

 the aloe. All these pigments are distinguished essentially from those 

 of chromoleucites by the fact that they do not turn blue with concen- 

 trated sulphuric acid. 



M. Courchet's observations confirm as a whole those of Schimper * 

 as to the structure and development of chromoleucites, though difiering 

 in some minor points. The crystals, whether natural or artificial, 

 furnished by orange pigments are all derived from the oblique rhom- 

 boidal prismatic form. Their orange-yellow, orange-red, or carmine- 

 red colour, and the corresponding tints which they communicate to the 

 organs, depend on the greater or less thickness of these formations or 

 on the molecular state of the pigment. This is shown by the facts that 

 solutions of these colouring substances in absolutely neutral solvents 

 have a constant orange-yellow colour, and that the variable tints pre- 

 sented by crystalline formations, whether natural or artificial, depend 

 on their thickness. 



Colouring-matter of Leaves and Flowers.f — Under this title Mr. 

 P. Sewell gives a summary of the state of knowledge in regard to vege- 

 table pigments, and communicates some suggestions as to their 

 physiological import. The first part of the paper discusses the physical 

 and chemical properties of the pigments. The second part deals with 

 colour- changes, which are grouped as follows: — (1) those induced 

 artificially by reagents, or naturally by the presence of substances of a 

 like nature; (2) those associated with particular environments ; (3) those 

 characteristic of definite conditions of growth. Of each of these 

 interesting illustrations are given. The third part of the paper reviews 

 the various hypotheses suggested to explain colours and colour-changes. 

 The observations of Buchan, Darwin, Grant Allen, J. E. Taylor, and 

 others, are discussed. What Spencer pointed out as to the co-existence 

 of colour and of flowers is emphasized and elaborated. The author 

 agrees with Vines that colouring matters are physiologically waste 

 products, and maintains that in contrast to the green of chlorophyll, 

 "colour'' is to be regarded "essentially as a product of a destructive 

 metabolism (katabolism) in the cells in which it occurs." The autumn 

 tints, the colour of the young shoots of spring, the pigments of the 

 reproductive organs or flowers are expressions of relative katabolic 



* See this Journal, 1886, p, 640. 



t Trans. Bot. Soc. Edin., xvii. (1887-8) pp. 276-308. 



