wood. , 63 



bie into others, which at last may be reduced to a net- 

 work of longitudinal fibres similar to those which exist 

 in the bark. The Hemlock tree Pinus Canadensis, 

 after a long exposure to the atmosphere exhibits a good 

 specimen of layers thus subdivided, nor is it easy to dis- 

 tinguish the component layers from the annual circles. 

 The same thing may be observed in the stem of the 

 Cabbage, which has been exposed to the weather until 

 its divergent plates are decomposed ; leaving its con- 

 centric layers distinct from each other like the tubes 

 of a telescope. 



When minutely examined, the plates of silver grain 

 are found to be composed of parallel fibres closely 

 crowded together, and appearing like compressed cel- 

 lular membrane. We see therefore, that wood is com- 

 posed of longitudinal fibres forming ar.et-work, and cel- 

 lular tissue extending in a transverse direction, the two 

 iets of fibres being interwoven so as to make the entire 

 structure very compact, and thus corresponding to the 

 description of Grew, who compared one to the warp 

 and the other to the woof of a web. 



After it was ascertained that a new layer is annually 

 deposited, it became a question whether it was formed 

 by the bark, the wood, or according to the specula- 

 tions of Linnaeus from the pith. But the experiments 

 of Duhamel and Hope, have put this question forever at 

 rest. The former, introduced plates of tinfoil between 

 the bark and wcod of growing trees, carefully bind- 

 ing up their wounds, and suffering them to remain sev- 

 eral years without further molestation. He found in 

 all cases, the layers of new 7 wood exterior to the tin. 

 Dr. Hope's experiment is equally decisive. He made 

 a longitudinal incision on the branch of a Willow, so as 

 to detach the wood from the bark, leaving the latter in 



