57 
VEGETABLE PHYSIOLOGY.~No. 11. 
We resume our notice of this elegant branch of science at the point where 
we left it, (see No. LXI., p. 10,) and shall now pave the way to serious investi- 
gation, by an attenipt to elucidate terms, and thereby facilitate the progress of the 
student, Nothing tends so effectually to fix the mind, as a perfect compreliension 
of scientioc phraseology ; and nothing more clearly marks and distinguishes the 
ardent student, than that restless earnestness which seeks the knowledge of 
principles. The memory always retains those facts which the understanding 
comprehends. 
Referring to our former article, we perceive that there are two or three terms 
which require explication. They are in the mouth of every one ; but, like the 
phrases of botany, are too often mere sounds which convey no definite or in- 
telligible meaning. The alburnum^ or sap wood of trees, as we have shown, was by 
Mr. Knight pronounced to be the channel of the sap, through the medium of its 
cells. 
The term alburnum is purely Latin ; derived ultimately from alhus^ white. It 
was employed by Pliny to express that white and tender tissue which exists, and 
is yearly produced, between the bark and the wood. By citing the following 
passage (we believe from the pen of Professor Lir.dley), it will appear that 
physiologists now ratify the hypothesis of Mr. Knight. 
*' It is the principal channel through which the crude sap is conveyed from the 
roots into the leaves. It consists of little besides vegetable tissue, in which respect 
it differs from heart-wood^ or duramen" {dnra^ Latin ; hard, or hardened wood,) 
" which is vegetable tissue combined with solid secretions." 
The cellular organs of this tissue abound with juices ; but the incipient fibres, 
which finally harden and solidify, are comparatively dry and juiceless : the presence 
of sap in the cells, therefore^ affords a strong argument in favour of the theorj^. 
Associated with the term alburnum^ we meet with another — liber^ which may 
now be explained. It was used by Virgil, and in its original sense, applied solely 
to that loose, delicate substance, which is interposed between the alburnum and 
the proper bark. The ancient Romans made use of this inner bark {liber) of 
certain trees for their manuscripts, as they did not possess paper. Hence, we 
gather that liber^ when its meaning is confined to a book, is a term of comparatively 
modern acceptation. 
In common with that of the alburnum, a layer of liber is deposited yearly ; the 
latter being closely contiguous to, but exterior of the former. Thus the layer or 
soft tissue of liber, invests that of alburnuni ; both the one and tlie other are 
vehicles of vital fluids, though of a different character ; and both are annually 
separated and thrust apart by the interposed developments of each succeeding year. 
VOL. VI. NO. LXTII. I 
