E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
like berberry, being yellow, was supposed to cure the yellow jaundice. According to the doctrìne oj signatures, Nature labels every plant with a mark to show what it is good for. Red plants are good for fever, white ones for rigor. Hence the red rose is supposed to cure hæmorrhage. (See THISTLES.)