50 



ever the stem of full-grown plants be examined, larger or 

 smaller spots are here and there found, where the cells and 

 spiral vessels are filled with it. 



In the living root of the Madder only yellow colouring mat- 

 ter is observed, which fills in its dissolved state the various 

 elementary organs. In very young roots the colour is still 

 weak, but the older the plant the more intense it is. Here 

 therefore the yellow colouring matter is dissolved in the cel- 

 lular sap, an observation which I made some years ago in a 

 different plant in its young state. This yellow substance is 

 evidently of quite a distinct nature from Marquart's anthox- 

 anthin, which is mostly a resinous extractive of very difficult 

 solution. As soon as the yellow sap of the Madder root comes 

 in contact with the atmosphere it takes a red colour, and a 

 granular substance forms in this red sap. Even the cotyle- 

 dons, as soon as the young plant has come forth, contain in 

 their cellular tissue a yellow sap, which, on their being cut, 

 very soon took a deep red appearance. This change of the 

 yellow cellular sap, in fine sections placed under the micro- 

 scope for observation, M. Decaisne has elucidated by a num- 

 ber of drawings. The cells are seen with fainter or deeper 

 yellow saps, and in other cells this sap has taken a faint rosy 

 tint, while frequently some of the intermediate cells are still 

 quite yellow ; at other places the red sap has already become 

 deeper, and has formed a granular precipitate in the cells. 

 When recent roots of the Rubia were perfectly dried and then 

 microscopically examined, he observed that, although all 

 moisture had disappeared, the cells still exhibited a yellow 

 colour ; whence he concluded, that the colouring substance is 

 a solid, which was previously in a dissolved state in the sap, 

 yet he could not observe it as a distinct body. I have not, 

 it is true, examined the roots of the Rubia, but in the yellow- 

 coloured cells of the stalk the same may be observed ; and here 

 the yellow colouring substance, after the water of the sap has 

 been evaporated, is partly absorbed by the sides, while the re- 

 maining portion rests on their surface. 



M. Decaisne also performed various experiments in order 

 to learn more accurately the causes which changed the yellow 

 sap of the fresh RubitE, as soon as it came in contact with at- 

 mospheric air, into red. He placed fine sections of the root in 



