236 THE SOLID COMPONENTS OF PLANTS. 



number of the ligneous fibres in each bundle of layers 

 and the force of their cohesion, the wood of different 

 trees possesses a greater or less degree of hardness. 

 But, although wood is found of various degrees of 

 consistence, yet it is probable that the ultimate fibre 

 may be the same in all plants. 



Whether the ligneous fibre be of original formation, 

 or condensed membranous or cellular texture, or an 

 obsolete obstructed vessel, as Hedwig reasonably sup- 

 poses, is yet undetermined. It is so intimately united 

 with the cellular texture containing the vegetable se- 

 cretions, that it cannot be procured pure for examina- 

 tion, without the separating aid of chemical agents. 

 If a thin shaving of well dried wood be first digested in 

 boiling water, then in alcohol, and lastly in ether, 

 every thing soluble in it will be extracted by these 

 liquids, and the insoluble part which remains be found 

 to be composed of interlaced fibres, easily subdivided 

 and having some degree of transparency : these are 

 the ligneous fibres. They have neither taste nor 

 odor, and remain unaltered by exposure to the at- 

 mosphere : but although insoluble in water, alcohol, 

 or ether, the fixed alkalies and mineral acids dis- 

 solve and decompose them. The relative quanti- 

 ty of this fibre in any plant may be pretty accurately 

 ascertained, by exposing a given quantity of the wood 

 to a moderate fire, in close vessels, for a number of 

 hours sufficient to convert it into charcoal ; for as the 

 wood only becomes charcoal and the other parts are 

 dissipated, the proportional weight of the charcoal ob- 

 tained shows the quantity of the ligneous fibre contain- 

 ed in the wood. Count Rumford thus found, that the 

 wood of the Poplar, Lime, Fir, Maple, Elm, and Oak, 

 contained each a proportion of ligneous fibre nearly 

 equal to 9 twentieths of their wood in its natural state. 



