On the Origin and Office of the Alburnum of Trees. 301 



lulaire of Duhamel and Mirbel) which expands and contracts 

 with change of temperature* after the tree has ceased to 

 live, might produce similar effects by occasioning nearly a 

 similar motion and compression of the tubes, the coats of 

 which are, I believe, universally admitted not to be mem- 

 branous. But both these hypotheses are inconsistent with, 

 the facts that I hav row the pleasure to communicate to 

 you. 



Selecting parts of the stems of young trees,' from which, 

 annual branches had sprung in the preceding year, I ascer- 

 tained by injecting coloured infusions into the stems, through 

 the annual shoots, that the tubes which descended from the 

 latter, were, at their bases, confined to that side of the stem 

 from which they sprang, and to the external annual laver of 

 wood. Deep incisions were then made into the stems of 

 other trees immediately beneath the bases'. of similar annual 

 shoots, by which I am quite confident that all communica- 

 tion through the alburnous tubes, with the stem, was wholly 

 cut off: yet the sap passed into the annual shoots in the 

 succeeding spring, all of which lived, and some grew with, 

 considerable vigour. I, at the same time, selected many- 

 lateral branches, about three lines in diameter, in a nursery 

 of apple trees, which I could easily secure to the stems of 

 the adjoining trees to prevent their being broken. I then 

 made an incision, more than two lines dcir> in each, on one 

 side, and at the distance of six or seven lines another inci- 

 sion, equally deep, on the opposite side; and as I am quite 

 certain, from the texture of these branches, that the albur- 

 nous tubes passed straight through them, lam equally cer- 

 tain thajL every alburnous tube was at least once intersected. 

 Yet the sap passed into these branches, and their buds un- 

 folded in the succeeding spring, the incisions having been 

 made in the winter. But I have repeated the same -experi- 

 ment after the leaves have been full grown in the summer,- 

 and still the branches have continued to live. 

 . All naturalists have agreed in stating that trees perspire 

 most in the summer, when their leaves have attained their 



* Philosophical Transa '; •- ■ : 15. 



