THE INNER ORGANIZATION OP TREES. 49 



entirely in the form of brittle plates. The innermost layers 

 of wood, and the outermost layers of bark, are therefore, 

 after a certain period, both deprived of life. The cork tree 

 (Quercus suber) however, is an exception. On the stem of 

 this tree which is cultivated in Spain, Portugal, and the 

 South of France, the bark grows to a considerable thickness, 

 and is removed from the tree every eight or ten years. It is 

 taken off in sheets or tables, much in the same way as oak or 

 larch bark is removed. After being detached it is flattened, 

 by presenting the convex side to heat or pressure. In either 

 case it is charred on both surfaces, to close the transverse 

 pores previously to its being sold. The carbonized surface 

 produced by this charring may be seen in bungs and taps, 

 but not in corks, which being cut in the direction of the 

 wood, the charring is taken off in the rounding. The dead 

 bark is taken off for the first time when the tree is about 

 fifteen years old ; it soon grows again, and the tree may be 

 rebarked three times, the bark improving every time until 

 the tree attains the age of thirty years. 



The old, dead, and fissured bark on the exterior surface of 

 yon aged tree, was once a young, living, and continuous 

 tissue in immediate contact with the wood, and has been 

 gradually separated from it, by the subjacent growth of suc- 

 cessive strata, or rather annual generations of bark cells. 

 Life has in succession passed from these away. The older 

 and more exterior, shelter the younger and more internal 

 bark cells. Vegetative life is at present,* torpid and inac- 

 tive, and the snow covers the ground; but the sun shall 

 again shine bright and warm on that now leafless tree, and 

 under its influence another generation of young and vitally 

 active bark cells shall develope, and be pushed forward to 

 die on the exterior of the stem and be ultimately thrown off 

 like the generations which have preceded them. 



From the whole of these facts it may be inferred, that the 

 life of a tree depends on a harmonious working together of 

 both its living and dead cells, the latter remaining not only 

 as a mechanical prop or foundation for new generations, like 



* This passage was written in the winter 'of 1857. 



7 



