148 ON THE INCONVERTIBILITY OF BARK INTO ALBUMEN. 



the conclusions they have dra\vn ; and I think that were bark really 

 transmuted into alburnum, its progressive changes could only have 

 escaped the eyes of prejudiced or inattentive observers. In the course 

 of the ensuing spring, I hope to address to you some observations respect- 

 ing the manner in which the alburnum is generated. 



XL ON THE ORIGIN AND OFFICE OF THE ALBURNUM OF TREES. 

 [Read before the ROYAL SOCIETY, June 30, 1808.] 



IN my last communication I endeavoured to prove that the bark 

 of trees is not subsequently transmuted into alburnum ; and if the 

 statements that I have there given be correct, they are, I conceive, deci- 

 sive on the point for which I contended : and if the bark be not converted 

 into alburnum, the experiments of Duhamel and subsequent naturalists, 

 and those of which I have given an account in former memoirs, afford 

 sufficient evidence that the bark deposits the alburnous matter. If the 

 succulent shoot of a horse chestnut, or other tree, be examined at suc- 

 cessive periods in the spring, it will be seen that the alburnum is depo- 

 sited, and its tubes arranged, in ridges beneath the cortical vessels ; and 

 the number of these ridges, at the base of each leaf, will be found to 

 correspond accurately with the number of apertures through which the 

 vessels pass from the leaf- stalks into the interior bark, the alburnous 

 matter being apparently deposited (as I have endeavoured to prove in 

 former memoirs) by a fluid which descends from the leaves, and subse- 

 quently secretes through the bark*. I shall therefore venture to con- 

 clude that it is thus deposited, and shall proceed to inquire into the 

 origin and office of the alburnous tubes. 



The position and direction of these tubes have induced almost all 

 naturalists to consider them as the passages through which the sap 

 ascends ; and at their first formation, when the substance which surrounds 

 them is still soft and succulent, they are always filled with the fluid, which 

 has apparently secreted from the bark. They appear to be formed in 

 the soft cellular mass, which becomes the future alburnum, as recepta- 

 cles of this fluid, to which they may either afford a passage upwards, 

 or simply retain it as reservoirs, till absorbed, and carried off, by the 

 surrounding cellular substance. The former supposition is, at first view, 

 the most probable ; but the latter is much more consistent with the cir- 

 cumstances that I shall proceed to state. 



* See above, No. II. 



