260 THE ANATOMY OF STEMS. 



the wood ; and in others, although they do not actu- 

 ally coalesce, yet they approach so close as almost to 

 assume the same character. As the stem increases, 

 these vascular bundles become impervious, and are 

 pushed outward with the cellular integument, giving 

 place to a new layer which is annually produced. 



4. Inner bark. Immediately under the vascular 

 bundles, we find another layer, which constitutes the 

 internal boundary of the bark. In the transverse sec- 

 tion of the stem of the Horse Chesnut it appears, un- 

 der the microscope, to consist of the extremities of 

 longitudinal fibres closely united together ; and, in 

 the tangental section, these fibres are seen running in 

 a waving direction and touching each other at certain 

 points, only so as to form oblong meshes, which are 

 filled with cellular matter. This layer is denominat- 

 ed liber, a name imposed from its having been em- 

 ployed to write on before the invention of paper. As 

 the net work formed by the dividing threads of the 

 meshes is not readily dissolved in water, whilst the 

 cellular matter which fills them up is remarkably so- 

 luble, the liber of some plants, for example the Daph- 

 ne Lagetto (or Lace tree), when soaked in water and 

 afterwards beaten, forms a very beautiful vegetable 

 gauze ; which may be used as an article of dress. A 

 coarser 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. 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. Like the other 

 parts of the bark, the liber is annually reproduced. 



