272 M. Decaisne on the Root of the Madder. 



duated tubes plunged in the mercury, in which I deposited thin 

 segments of fresh madder root cut both vertically and hori- 

 zontally, and they remained there eight days without exhibit- 

 ing the slightest change of hue. But when by means of a blow 

 pipe I introduced a few drops of water into the tube of oxygen 

 gas, the red colour was instantly produced. Carbonic acid 

 gas did not appear to me to exhibit the same peculiarities ; and 

 certainly the oxygenated water, whether applied to the roots 

 in a fresh or dry state, failed to effect the change to red at all 

 more quickly than as much common water would have done. 



Thin slices of young roots, when exposed for some hours to 

 the air, after undergoing the customary transitions of tint, 

 often acquire a blackish or violet hue which is not observable 

 in old roots. 



From all that has been stated, it results that the madder 

 root, when living, has no colour but yellow, and that this co- 

 louring principle only varies by the deepening intensity of 

 age. These different degrees of intensity are represented 

 in the series of drawings, where I have represented the varia- 

 tion of hue in the roots from the young to the old state. This 

 observation is easily verified; nothing more is necessary than 

 to break two roots of different ages and to watch the change 

 of hue from that instant till the air begins to take effect ; the 

 fluid will then be seen to be perfectly transparent while in- 

 closed in the cells, but shortly this pellucid and pure liquid 

 will become muddy and granulated so as to darken the parts 

 of the cells with which it comes in contact. These granules, 

 which seem to me to partake of the nature of gum resins, are 

 partly soluble in alcohol ; but as the dye of iodine fails to im- 

 part to them a blue colour, they do not show any identity with 

 feculum. Their diameter is nearly equal, but they are inap- 

 preciable except in a mass, when insulated being hardly visible, 

 as even with the aid of an excellent microscope divided in 

 300dths of millimetres, it was impracticable, by reason of their 

 tenuity, to measure them precisely. 



The madder roots many years old contain no coloured 

 parts except what I have now pointed out, whether the plant 

 be examined dry or after the exsiccated portions have been 

 subjected to maceration. The existence of a yellow colour is 



