35 OF THE WOOD, 



also to be mentioned, that by performing this 

 experiment of engrafting a portion of bark at 

 different periods through the spring and sum- 

 mer, the same accurate observer found a 

 great difference in the thickness of the layer 

 of new wood produced under it, which was 

 always less in proportion as the operation 

 was performed later in the season. 



That, the bark or liber produces wood 

 seems therefore proved beyond dispute, but 

 some experiments persuaded Du Hamel that 

 in certain circumstances the wood was capa- 

 ble of producing a new bark. This never 

 happened in any case but when the whole 

 trunk of a tree was stripped of its bark. 

 A Cherry-tree treated in this manner exuded 

 from the whole surface of its wood in little 

 points a gelatinous matter, which gradually 

 extended over the whole and became a new 

 bark, under which a layer of new wood was 

 speedily formed. Hence Mirbel concludes, 

 vol. 1. 176, that the alburnum and the 

 wood are really the origin of the new layers 

 of wood, by producing first this gelatinous 

 substance, or matter of organization, which 

 he and Du Hamel call cambium, and which 



