LECT. III.] GENERAL FLUID COMPONENTS. 117 



faces, but in greatest quantity from the open ori- 

 fices of the divided vessels in the part farthest from 

 the root ; a fact which is ascribable to the progres- 

 sion of the proper juice being invertedly to that of 

 the sap, or from the leaves towards the roots. It is 

 very often mixed with sap, and cannot be distin- 

 guished from it by colour ; but in many instances 

 it is coloured 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 obtained in 

 considerable quantity. This juice in the majority of 

 plants is, as I have said, colourless ; it is, however, 

 yellow in some, as in the Celandine (Chelidonium); 

 red in others, as in the Bloody Dock (Rumex san- 

 guinea) and the Logwood tree (Hsematoxylon) ; 

 deep orange in the Artichoke (Cynara Scolymus) ; 

 white, as in the Spurges (Euphorbia), the Dande- 

 lion (Leontodon Taraxacum)., the Fig (Ficus), 

 &c. ; blue in the root of Pimpernell (Pimpinella 

 nigra) ; and green in the Periwinkle (Vinca). The 

 colour is sometimes changed by the exposure of the 

 exuded juice to the air. Thus Opium, which is 

 the proper juice of the white Poppy, is white and 

 milky when it exudes from the incisions made in 

 the plant for the purpose of obtaining it; but 

 changes to a yellowish brown hue by exposure to 

 the air. The plantule also of the French or Ha- 

 ricot Bean, when wounded, emits a reddish proper 



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