THE ORGANIC ELEMENTS. 27 



are frequently soluble in ether, alcohol, volatile oils, and separated from 

 ether in a resinous, not in a fatty, form. The first, as far as I know, are 

 only of a red and blue colour ; the red caused by an acid, the blue by an 

 alkali ; and are dissolved in the fluid contents of the cell. They may be 

 found in the red parts of plants, and in the flowers of Echium vulgare. 

 They all contain nitrogen.* But there are other colouring matters 

 present in plants, as the red in Iberis umbellata, and the blue in violets, 

 which become green through the action of alkalies, and which are very 

 different from the foregoing. Chemistry has much to do in this depart- 

 ment of inquiry. 



A theory was proposed in 1834, by Clamor Marquart, in a book on 

 the colours of plants, which supposed that two modifications of chlo- 

 rophyll, Anthoxanthin and Anthocyan, the one containing a little more, 

 and the other a little less, water than chlorophyll, were the cause of the 

 red and yellow series of colours, and chlorophyll of the blue. Although 

 this theory is adopted by Endlicher and linger, in their " Rudiments of 

 Botany," it is not founded on sufficiently accurate data to demand refuta- 

 tion. Berzelius (Handbuch der Chemie) and Mulder (Physiol. Chem.) 

 have both written on Chlorophyll, and I have mostly followed the latter 

 in the foregoing remarks. The remaining colouring matters important 

 in the arts, but unimportant physiologically, demand attention. 



3. Tartaric Acid (Acidum tartaricum, T.), Citric Acid (Acidum ci- 

 tricum, Ci.), and Malic Acid {Acidum malicum, Ma.), are either found 

 together or alone in all sour fruits, and perhaps also in all acidulous 

 juices of plants, for malate of lime is found in the Sempervivum tectorum. 

 From the process of ripening in fruits, it has been concluded that these 

 acids stand in a peculiar relation to sugar ; that they are easily formed 

 out of it, and as easily pass into it. Liebig (Organic Chemistry) has gone 

 so far as to presume that, in the presence of alkalies, carbonic acid 

 and water are converted into hydrated oxalic acid, and this into tartaric 

 acid, malic acid, and, lastly, this into sugar and dextrin ; and that thus 

 the organic acids stand in a middle place between the organic and in- 

 organic bodies. This is one of Liebig's most genial combinations, but 

 has no observation on which to rest. The chemical composition of these 

 acids, according to Berzelius and Liebig, is as follows : 



C H O 



Tartaric Acid - - - 8 4 10 



Citric Acid - - 12 4 12 



Malic Acid - - - 8 4 8 



4. The Alkaloids, like the acids, are, as far as we know at present, 

 only so far important as the remarks of Liebig (Organic Chemistry), on 

 both classes of substances, extend. Many plants appear to have a 

 facility, when it is necessary to neutralise a base by an inorganic acid, or 

 an acid by an inorganic base, and these substances fail, of substituting 

 for them organic acids and bases. Thus we find that potatoes sprouting 

 away from the soil form Solanin ; thus Quinine, Cinchonine, and Lime, 

 take the place of each other in the Cinchona barks, and Meconic acid is 

 found in opium to take the place of Sulphuric acid. 



5. Tannin (Tannic Acid). In most plants, and especially the Pha- 

 nerogamia and Ferns, there is frequently found a substance which red- 

 dens litmus, tastes astringent, and changes animal gelatine into leather. 

 This substance appears to be modified in different plants. It is found 



* "According to Liebig, Organic Chemistry. 



