M. Decaisne on the Root of the Madder, 271 



part of the cellular tissue contiguous to the vessels of the 

 latex ; next in the cells occupying the intervals of the dotted 

 vessels in the centre of the root ; and lastly in the various 

 parts of the cellular tissue which compose the fleshy portion, 

 and which is the principal deposit of the yellow fluid. 



It is easy to understand these phasnomena in a thin layer 

 of root, and to explain the production of the red hue in these 

 determinate places ; the air passes most freely, and conse- 

 quently with the greatest rapidity, into the part filled with 

 vessels, the cutting open of which, at both ends, makes a free 

 way for it, and where it meets with no obstruction from the 

 transverse diaphragms that exist in the cellular tissue. The 

 proper vessels situated immediately next to these, and habit- 

 ually replete with liquid, and protected with very thin parietes 

 through which any gas can readily take effect, will be the first 

 to become coloured, as well as the spaces comprised between 

 these vessels and those to which I formerly alluded ; while, 

 lastly, the cellular tissue being composed of numerous super- 

 incumbent cellules, and thus offering many impediments to 

 the action of the air, it is easy to perceive that the most ex- 

 ternal cellules will first receive its influence, and that in the in- 

 termediate layers there will be portions on which it can only 

 act after a longer or shorter time, and of which the colour will 

 consequently remain yellow while the cellules around have 

 assumed a red colour. Those cells which lie on the thin edges 

 of the section are always first tinged, evidently because the 

 air affects them first. It is practicable too to alter at will the 

 hue of one or more cells, to effect which it suffices to remove 

 a thin slice from a previously dried root, some cells remaining 

 uninjured ; then, if with great precaution certain cells be 

 punctured with a curved point, so as to admit the entrance of 

 the air, the yellow fluid with which they are filled will be seen 

 to pass instantly to red. I have also placed some sections of 

 madder root in water which had been exhausted of air by the 

 operation of boiling, and in this case their originally yellow 

 hue remained entirely unaltered, the utmost care having been 

 previously taken to keep these sections of root in tightly closed 

 bottles, without which they redden slightly. 



I have tried the action of different gases collected in gra- 



