CHAP. III. ORIGIN OF 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 adliex'ing 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 bi'anch 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 frorti 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 Thenars, a bi'anch of Robinia 

 Pseudacacia on which R. hispida had been grafted. The stock 



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