IO6 VEGETABLE SUBSTANCES. 



litmus. After the prolonged action of alkalies 

 the blue passes into a green, yellowish-green, or 

 yellow. But it has been thought that the latter 

 tints are produced in consequence of the presence 

 of tannin in the cell-sap, which gives a green color 

 with iron, and which may give the yellow potassic 

 hydrate reaction in the color mixture. 1 



In Strelitzia Reginoe and Tillandsia amoena, 

 Hildebrand found anthocyanin diffused in small 

 grains, which were soluble in potash, alcohol, and 

 ammonia ; which iodine colored brown ; and which 

 were, therefore, probably of a protoplasmic nature. 



It is doubtless worthy of mention here that 

 anthocyanin may form, with metallic salts, an 

 insoluble compound of a green (Fremy and Cloez) 

 or blue (Wiesner) color. Certain cells (Gentiana 

 verna) containing anthocyanin, which have first 

 been reddened by acids that have then been re- 

 moved by rinsing with distilled water, assume a 

 blue color with a solution of chloride of iron. 

 Since, however, the same phenomenon occurs with 

 acetate of lead, tannic acid can have nothing to 

 do with it. 



ALIZARIN 2 



Forms yellow masses in the fresh cells of madder- 

 root. With the access of air it soon becomes red 



1 Sachsse's objections, however, should be compared with this, /. c ., p. 76. 



2 Decaisne: Recherches anat. et physiol. sur la Garance et le deve- 

 loppement de sa matiere colorante, 10 pi., Bruxelles, 1837. Rosenstiehl: 

 Ann. de Chim. et de Phys., 5 Ser., T. XIII., p. 148. 



