CHAP. III. ORIGIN OP WOOD. 261 
but that it is produced from matter elaborated in the leaves 
and sent downwards — either through the vessels of the inner 
bark, along with the matter for forming the liber by which 
it is subsequently parted with ; or that it and the liber are 
transmitted distinct from one another, the one adhering to the 
alburnum, the other to the bark. I know of no proof of the 
former supposition ; of the latter there is every reason to 
believe the truth. Knight is of opinion that two distinct 
sets of vessels are sent down, one belonging to the liber, the 
other to the alburnum ; and if a branch of any young tree, 
the wood of which is formed quickly, be examined when it is 
first bursting into leaf, these two sets may be distinctly seen 
and traced. Take, for instance, a branch of lilac in the be- 
ginning of April and strip off its bark : the new wood will be 
distinctly seen to have passed downwards from the base of 
each leaf, diverging- from its perpendicular course, so as to 
avoid the bundle of vessels passing into the leaf beneath it; 
and if the junction of a new branch with that of the previous 
year be examined, it will be found that all the fibres of wood 
already seen proceeding from the base of the leaves, having 
arrived at this point, have not stopped there, but have passed 
rapidly downwards, adding to the branch an even layer of 
fibrous matter or young wood ; and turning off at every pro- 
jection which impedes them, just as the water of a steady but 
rapid current would be diverted from its course by obstacles 
in its stream. Again, in Guaiacum wood, the descending 
fibres cross and interlace each other in a manner that is totally 
inexplicable upon the supposition of wood being formed by 
the mere deposit of secreted matter. If the new wood were a 
mere deposit of the bark, the latter, as it is applied to every 
part of the old wood, would deposit the new wood equally 
over the whole surface of the latter, and the deviation of the 
fibres from obstacles in their downward course could not 
occur. This, therefore, in my mind, places the question as 
to the origin of the wood beyond all further doubt. Or, if 
further evidence were required, it would be furnished by a 
case adduced by Achille Richard, who states that he saw, in 
the possession of Du Petit Thouars, a branch of Robinia 
Pseudacacia on which R. hispida had been grafted. The stock 
s 3 
