VEGETABLE PHYSIOLOGY. 17 



tills them up is remarkably soluble, the liber of some plants, as 

 the Lace tree, (Daphne Lagetto), when soaked in water and 

 afterwards beaten, forms a very beautiful vegetable gauze ; 

 which may be used as an article of dress. A coarse specimen 

 of this gauze, or lace, is seen in the bark of many of our 

 indigenous trees, particularly the oak, when it has been long 

 exposed to the weather, after being separated from the trunk. 

 The natives of Otaheite manufacture garments from the liber of 

 the mulberry. The liber of flax is by a more refined process 

 converted into linen. This regular arrangement, however, of 

 the longitudinal texture of the liber is not found in every instance ; 

 for on the fir and some other trees, the longitudinal threads are 

 seen lying nearly parallel to one another, without any meshes or 

 intervening cellular matter. 



This part of the bark is important to the life of Vegetables ; 

 the outer bark may be peeled off without injury to them, but the 

 destruction of the liber is generally fatal. The operation of 

 girdling trees, which is often practised in new countries, consists, 

 in making with an axe, one or more complete circles through 

 the outer bark and the liber of the trunk. Trees seldom survive 

 this operation, especially if it has been performed early in the 

 spring, before the first flow of the sap from the root towards the 

 extremities. 



5. The alburnum, or sap wood, which may be considered 

 the grand vascular organ of the plant, which is made up of cells 

 and tubular vessels ; the cells being constantly filled with the 

 rising sap, which, after undergoing some changes, is taken up 

 by the tubes and conveyed to the leaves to their utmost extremity ; 

 and having from them received a new modification, the sap is 

 returned by the cortical vessels back to the trunk, and thence to 

 the minutest filaments of the roots. 



The alburnum is at first soft and vascular ; but it afterwards 

 becomes hard, and in some trees, is of a density almost equal to 

 iron. While in the soft state, it is endowed with nearly as much 

 irritability as the liber, and performs functions of great importance 

 in the vegetable system ; but when hardened, these functions 

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