270 M. Decaisne on the Root of the Madder. 



an extraordinary circumstance, as they may be frequently found 

 in other plants. 



It remains for ns to sec what are the phenomena that take 

 place id the fluid that is diffused through the whole cellular 

 tissue ofthejroot. It has been already remarked, that the roots, 

 which, when very young, are pale yellow, assume a much 

 deeper hue when old. If this fluid be carefully examined, it 

 will not appear to hold any substance in solution; and whether 

 it escapes through the partitions of the cells or by an incision 

 purposely made, it still seems perfectly limpid. As, however, 

 when the root is thoroughly dried, the internal cells, though 

 all the fluid has evaporated, still assume a yellow tint if laid 

 to steep, it would appear that the liquid had originally pos- 

 sessed a solid colouring principle, though, even in this state, 

 such is its tenuity, that the largest swellings do not allow it to 

 be seen. 



It is of course presumed in the above observations, that 

 the different parts have been subjected to no external agency 

 whatever, as such agency produces great changes ; for in- 

 stance, after having made sections, whether vertical or hori- 

 zontal, of a young root, and subjected them to microscopical ex- 

 amination, this juice, which is so perfectly limpid in the living 

 plant, presently becomes thick and cloudy, while its originally 

 pale yellow tint changes to a bright rose colour. Experiments 

 on older roots yield the same results, except that as in these 

 cases the yellow fluid is originally much brighter, so its change 

 to red when exposed to the air becomes proportionably in- 

 tense, and instead of acquiring, as in the preceding case, a 

 roseate tint, the result, from an orange colour, is a change to 

 the most vivid red. 



If attention be paid to the circumstances under which this 

 red colour is obtained, which did not exist before the section 

 of the parts, we cannot but suspect that the action of the air, 

 which was previously excluded, is the cause more or less of 

 this change, and an increased number of experiments confirms 

 this opinion. In a thin layer the modifications occasioned by 

 the external air on the yellow colour may be successively 

 traced ; the red tinge always manifesting itself first in that 



