THE FLUID COMPONENTS OF PLANTS. 245 



The Proper Juice. 



When a plant is cut through transversely, the prop- 

 er juice is seen issuing from both divided surfaces, but 

 in greatest quantity from the open orifices of the di- 

 vided vessels in the part farthest from the root ; a fact 

 which is ascribable to the progression of the proper 

 juice being inverse to that of the sap, or from the 

 leaves towards the roots. It is very often mixed with 

 sap, and cannot be distinguished from it by color ; but 

 in many instances it is colored or milky. Thus, if a 

 twig of any of the species of Spurge [Euphorbia) be 

 cut, the proper juice issues from the wound in the 

 form of a resinous milky emulsion, and may be ob- 

 tained in considerable quantity. This juice in the ma- 

 jority of plants is, as has been said, colorless ; it is, 

 however, yellow in some, as in Celandine (CAe- 

 lidonium) ; red in others, as in the Blood-root [San- 

 guinaria), the Bloody Dock (Rumex sanguinea), and 

 the Logwood tree (Hamatoxylon) ; deep oranse in 

 the Artichoke ( Cynara Scolymus) ; white, as in the 

 Spurges, the Dandelion (Leontodon Taraxacum), the 

 Fig, the Poppy, Sic. blue in the root of Pimpernel! 

 (Pimpinella nigra) ; and green in the Periwinkle 

 (Vinca). The color is sometimes changed by ex- 

 posure to the air. Thus opium, the proper juice of 

 the Poppy, is white and milky when it exudes from 

 the incision, but changes to a yellowish brown hue by 

 exposure to the air. The juice which exudes from 

 incisions in the leaves of the Soccotrine Aloe, yields, 

 by simple exposure, according to the statement of M. 

 Fabroni, a very deep and lively purple dye, so per- 

 manent, and resisting so completely the action of acids, 

 alkalies, and oxygen gas, as to offer an useful pigment 

 in miniature painting ; or as a dye for silk, which it 

 will effect without the use of any mordant. 

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