THK COLOURING PRINCIPLES OF PLANtS. 53 



until the juice has been thoroughly extracted. The juice, mixed with quicklime, in 

 then transferred to large boilers, where it is evaporated, and afterwards set aside to 

 crystallize. The larger portion of the sugar is thus separated from the fluids in which 

 it was secreted; but a considerable quantity remains uncrystallized in the mother- 

 liquor, and constitutes the molasses so abundantly used in those climates as food, and 

 for the distillation of rum. The colour of the sugar is more or less brown, and is 

 purified either in this country or in the country of its production, by filtration 

 through animal charcoal. Bullock's blood was formerly used for this purpose. The 

 coloured uncrystallized liquor which then remains is the treacle of commerce. 



We may mention that, as a curiosity, some cane sugar was made from sugar-cane 

 grown in this country, and exhibited at the Great Exhibition of 1851. 



Good specimens of giape sugar were forwarded to the Great Exhibition from Tunis 

 and the Zollverein States. Palm sugars have hitherto been mere curiosities, but they 

 have been made from the date palm of the Deccan, the Gomutus palm (Arenga sacchari- 

 fera] of Java, the Nipa palm stem, and the flower of the Bassia latifolia, and might, 

 doubtles, be procured from all palms yielding refreshing and fermenting juices. 



Colouring Principles. The colours presented by plants are exceedingly varied, 

 and all alike depend upon the presence of colouring principles in the cells of colourless 

 tissue. 



There are eight principal colours recognised in vegetables viz., white, gray, brown, 

 yellow, green, blue, red, and black; and each of these has many distinct shades. 



Of these shades of colour, nine have been associated with white : pure, snow, ivory, 

 chalk, and milk white ; with silvery, whitish, turning white, and whitened. 



A similar number is also attributed to gray, and are designated ash, lead, slate, and 

 pearl gray ; smoky, hoary, and rather hoary, and mouse-coloured. 



Twelve have been computed in connexion with brown ; viz., brown, chestnut, deep 

 and bright brown, rusty, red, brown, rufous and cinnamon-coloured, with lurid, sooty, 

 and liver-coloured. 



Yellow has twenty shades ; thus, lemon, yellow, golden, pale, leather, waxy, and 

 Isabella yellow ; sulphur, straw, ocre, orange, apricot and saffron-coloured ; testaceous, 

 tawny, and livid. 



There are seven varieties of green, of the shades of olive, grass, sea, yellowish, 

 apple, meadow, and leek. 



Bed has seventeen shades : carmine, rosy, purple, sanguine, scarlet, eumaba, vermil- 

 lion, coppery, brick, flame-coloured, &c. ; whilst its compound blue has but seven viz., 

 pmssian, blue, indigo, lavender, violet, lilac, and sky blue"; and black has four: pure, 

 coal, raven, and pitch black. 



Thus as many as eighty-six different shades of colour have been determined to 

 exist in plants; but only two chemical colouring principles have been discovered viz., 

 chlorophyl and chromule. 



Chlorophyl is so called from its imparting a green colour to plants ; that is, that 

 kind of green which is universally met with in all plants growing in the light. It is 

 distributed to the tissues themselves, but more particularly to the surface of the starch 

 cells, which are abundant in all green plants. 



Chromule is the general term for the colouring principle of all other colours, 

 although they may be so closely approximated that adjoining cells may have totally 

 different colours. 



Dyes. Another highly important series of vegetable secretions are such colouring 



