THE EEASON WHY. 321 



" And all the trees of the field shall know that I the Lord have brought down the 

 high tree, have exalted the low tree, have dried up the green tree, and have raade 

 the dry tree to flourish : I the Lord have spoken, and have done it. EZEK. xvn. 



Man assists this evident intention of nature, by slitting the bark 

 from the top of the tree to its base ; but even were this not done, 

 the bark would be cast off by the tree itself 



Another proof of design in this useful adaptation of the cork - 

 tree is to be found in the fact, that it thrives under treatment that 

 would destroy other trees. The cork-tree will endure the barking 

 process for seven or eight successive years. 



CHAPTER LXIV. 



1273. Why are there curious markings in walnut, maho- 

 gany, rose-ivood, satin-wood, c. ? 



Because those markings are produced by the various structure of 

 the vessels by which the wood is formed ; and by successive zones 

 of wood, which indicate the periods of growth. 



The inclosure of zone within zone is owing to the mode in which the wood is 

 produced, and the position in which it is deposited. Wood is formed by the 

 leaves during the growing season, and passes down towards the root between 

 the bark and the wood of the previous year (if any), or in the position in which 

 cambium is effused ; and, as the leaves more or less surround the whole stem, 

 the new layer at length completes a zone, and perfectly encloses the wood of all 

 former years. This is the explanation of the term exogenous, which is derived 

 from two words signifying to grow outwardly, for the stem increases in thickness 

 by successive layers on the outer side of the previously-formed wood. That 

 this is the mode of growth has been abundantly proved by experiment, and de- 

 monstrated by accidental discoveries. Thus, if a plate of metal be inserted 

 between the bark and wood, it will, in progress of time, become inclosed by the 

 new wood which has overlaid them. So in like manner if letters be cut deeply 

 through the bark and into the wood, the spaces will not be filled up from the 

 bottom, but may be seen in subsequent years overlaid by new wood. A state- 

 ment appeared in a daily paper, during the past year, to the effect that in cut- 

 ting down a tree a cat had been discovered inclosed in the wool of the trunk, 

 These facts prove that the wood is applied from without. Again, if a branch be 

 stripped of its leaves down to a cortaia point, it will not grow above that point ; 

 and so, in like manner, if branches bo stripped from one side of a tree, the tree 

 will not grow on that side. If a circle of bark be removed from a branch above 

 and also below a leaf, it will be found that increase of size will occur below, but 

 not above that bud ; and so, likewise, whenever a ring of bark is removed from a 

 tree, the new woody fibre will not proceed from the lower but from the upper 

 edge. Orr's Circle of the Sciences. 



14* 



