Each is also called Iris, as resembling the rainbow in beauty of colour. The land Flag (_Iris versicolor_) is well known as growing in swamps and moist meadows, with sword-shaped leaves, and large purple heads of flowers, bearing petals chiefly dark blue, and veined with green, yellow, or white. The water Flag (_Iris pseudacorus_) is similar of growth, and equally well known by its brilliant heads of yellow flowers, with blade-like leaves, being found in wet places and water courses. The root of the Blue Flag, "Dragon Flower," or "Dagger Flower," contains chemically an "oleo-resin," which is purgative to the liver in material doses, and specially alleviative against bilious sickness when taken of much reduced strength by reason of its acting as a similar. The official dose of this "iridin" is from one to three grains. A liability to the formation of gall stones may be remedied by giving one grain of the oleoresin (iridin) every night for twelve nights. A medicinal tincture (H.) is made which holds this Iris in solution; and if three or four drops are taken immediately, with a spoonful of water, and the same dose is repeated in half-an-hour if still necessary, an attack of bilious vomiting, with sick headache, and a [200] film before the eyes, will be prevented, or cut short. The remedy is, under such circumstances, a trustworthy substitute for calomel, or blue pill. Orris powder, which is so popular in the nursery, and for the toilet table with ladies, on account of its fresh "violet" scent, is made from the root of this Iris, being named from the genitive _ireos_. Louis VII. of France chose this Blue Flag as his heraldic emblem, and hence its name, _fleur de lys_, has been subsequently borne on the arms of France. The flower was said to have been figured on a shield sent down from heaven to King Louis at Clovis, when fighting against the Saracens. Fleur de Louis has become corrupted to _fleur de lys_, or _fleur de lis_. The Purple Flag was formerly dedicated to the Virgin Mary. A certain knight more devout than learned could never remember more than two words of the Latin prayer addressed to the Holy Mother; these were _Ave Maria_, which the good old man repeated day and night until he died. Then a plant of the blue Iris sprang up over his grave, displaying on every flower in golden letters these words, _Ave Maria_. When the monks opened the tomb they found the root of the plant resting on the lips of the holy knight whose body lay buried below.