444 CONSERVATIVE ORGANS. [*,ECT. VIII. 



the central parts of some medicinal roots are as 

 valuable as the cortical; although, in general, 

 the bark is that part of the root which is most 

 richly stored with the proper juices of the plant. 

 In examining unknown roots, when we find the 

 central part woody, we may always conclude that 

 it consists entirely of sap vessels, and therefore is 

 useless either as food or as medicine; but when it 

 is composed chiefly of a moist, cellular substance, 

 we may expect to find it useful, from having some 

 of the proper juice and secretions of the plant de- 

 posited in it. The ignorance of this fact, led 

 Pharmacopolists, until very lately, to expend un- 

 necessarily much labour and time in preparing 

 several vegetable decoctions and extracts, as, for 

 example, the decoction of sarsaparilla ; for the 

 preparation of which the root underwent long 

 macerations and much boiling, from an idea that 

 its virtues were contained in the ligneous central 

 part ; whereas the saponaceous mucus for which 

 it is valued, is deposited solely in the cortical 

 part, and can be entirely extracted by cold water. 

 In selecting the proper period for digging up 

 roots for medicinal purposes, it ought to be re- 

 collected that, as the proper juices which are 

 stored up in the roots of such plants as produce 

 leaves only in one year, and then flower and die in 

 the second, are expended in the process of fructi- 

 fication ; biennial roots should be taken up at the 



