Page:An introduction to physiological and systematical botany (1st edition).djvu/66

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also to be mentioned, that by performing this experiment of engrafting a portion of bark at different periods through the spring and summer, 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 capable 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