Our _Garden Rhubarb_ is a true Dock, and belongs to the "many-kneed," buckwheat order of plants. Its brilliant colouring is due to varying states of its natural pigment (_chlorophyll_), in combination with oxygen. For culinary purposes the stalk, or petiole of the broad leaf, is used. Its chief nutrient property is glucose, which is identical with grape-sugar. The agreeable taste and odour of the [160] plant are not brought out until the leaf stalks are cooked. It came originally from the Volga, and has been grown in this country since 1573. The sour taste of the stalks is due to oxalic acid, or rather to the acid oxalate of potash. This combines with the lime elaborated in the system of a gouty person (having an "oxalic acid" disposition), and makes insoluble and injurious products which have to be thrown off by the kidneys as oxalate crystals, with much attendant irritation of the general system. Sorrel (_Rumex acetosus_) acts with such a person in just the same way, because of the acid oxalate of potash which it contains. Garden Rhubarb also possesses albumen, gum, and mineral matters, with a small quantity of some volatile essence. The proportion of nutritive substance to the water and vegetable fibre is very small. As an article of food it is objectionable for gouty persons liable to the passage of highly coloured urine, which deposits lithates and urates as crystals after it has cooled; and this especially holds good if hard water, which contains lime, is drunk at the same time. The round-leaved Dock, and the sharp-pointed Dock, together with the bloody-veined Dock (which is very conspicuous because of its veins and petioles abounding in a blood-coloured juice), make respectively with their astringent roots a useful infusion against bleedings and fluxes; also with their leaves a decoction curative of several chronic skin diseases.