192 ORIGIN OF WOOD. [BOOK n. 



Hence the question as to the origin of the wood seemed 

 settled ; and there is no doubt that the experiments of Du- 

 hamel are perfectly accurate, and satisfactory as far as they 

 go. It soon, however, appeared, that, although they certainly 

 proved that new wood is not produced by old wood, it was 

 not equally clear that it originated from the bark. Accord- 

 ingly a new set of experiments was instituted by Knight, 

 for the purpose of throwing a still clearer light upon the 

 production of the wood. Having removed a ring of bark 

 from both above and below a portion of bark furnished with a 

 leaf, he remarked that no increase took place in the wood 

 above the leaf, while a sensible augmentation was observable 

 in the wood below the leaf. It was also found, that, if the 

 upper part of a branch be deprived of leaves, the branch will 

 die down to the point where leaves have been left, and 

 below that will nourish. Hence the inference was drawn, 

 that the wood is not formed out of the bark as a mere deposit 

 from it ; 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. Knight 

 was 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 beginning 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 the wood already seen proceeding from 

 the base of the leaves, having arrived at this point, has not 

 stopped there, but has passed rapidly downwards, adding to 

 the branch an even layer of young ligneous matter, and 

 turning off at every projection which impedes it, just as the 



