The Collaborative International Dictionary of English v.0.48:

Rumicin \Ru"mi*cin\, n. (Chem.)
   A yellow crystalline substance found in the root of yellow
   dock (Rumex crispus) and identical with chrysophanic
   acid.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dock \Dock\ (d[o^]k), n. [AS. docce; of uncertain origin; cf. G.
   docken-bl[aum]tter, Gael. dogha burdock, OF. doque; perh.
   akin to L. daucus, daucum, Gr. ?, ?, a kind of parsnip or
   carrot, used in medicine. Cf. Burdock.] (Bot.)
   A genus of plants (Rumex), some species of which are
   well-known weeds which have a long taproot and are difficult
   of extermination.
   [1913 Webster]

   Note: Yellow dock is Rumex crispus, with smooth curly
         leaves and yellow root, which that of other species is
         used medicinally as an astringent and tonic.
         [1913 Webster]