34 OF THE WOOD. 



Malpighi and Grew thought it was formed 

 by the bark, and the best observations have 

 confirmed their opinion. Hales supposed the 

 wood added a new layer to itself externally 

 every year. Linnaeus had a peculiar notion, 

 that a new layer of wood was secreted annu- 

 ally from the pith, and added internally to 

 the former ones. Truth obliges us to confess 

 that the latter theory is most devoid of any 

 kind of proof or probability. 



Du Hamel, by many experiments, proved 

 the wood to be secreted or deposited from 

 the innermost part of the bark or liber. He 

 introduced plates of tinfoil under the barks 

 of growing trees, carefully binding up their 

 wounds, and, after some years, on cutting 

 them across, he found the layers of new w r ood 

 on the outside of the tin. His original spe- 

 cimens I have examined in the public mu- 

 seum at Paris. 



Dr. Hope, the late worthy Professor of 

 Botany at Edinburgh, instituted an experi- 

 ment, if possible more decisive, upon a branch 

 of Willow three or four years old. The bark 

 was carefully cut through longitudinally on 

 one side for the length of several inches, so 



