130 



VIII. ON THE INVERTED ACTION OF THE ALBURNOUS VESSELS OF 



TREES. 



[Read before the ROYAL SOCIETY, May 15, 1806.] 



I HAVE endeavoured to prove, in several memoirs* laid before the 

 Royal Society, that the fluid by which the various parts (that are annu- 

 ally added to trees, and herbaceous plants whose organization is similar 

 to that of trees,) are generated, has previously circulated through their 

 leavesf either in the same or preceding season, and subsequently de- 

 scended through their bark ; and after having repeated every experiment 

 that occurred to me, from which I suspected an unfavourable result, I am 

 not in possession of a single fact, which is not perfectly consistent with the 

 theory I have advanced. 



There is, however, one circumstance stated by Hales and Duhamel, 

 which appears to militate against my hypothesis ; and as that circum- 

 stance probably induced Hales to deny altogether, the existence of 

 circulation in plants, and Duhamel to speak less decisively in favour of 

 it than he possibly might otherwise have done, I am anxious to recon- 

 cile the statements of these great naturalists, (which 1 acknowledge 

 to be perfectly correct,) with the statements and opinions I have on 

 former occasions communicated to you. 



Both Hales and Duhamel have proved, that when two circular 

 incisions through the bark, round the stem of a tree, are made at a 

 small distance from each other, and when the bark between these 

 incisions is wholly taken away, that portion of the stem which is below 

 the incisions through the bark continues to live, and in some degree 

 to increase in size, though much more slowly than the parts above the 

 incisions. They have also observed, that a small elevated ridge (bour- 

 relet) is formed round the lower lip of the wound in the bark, which 

 makes some slight advances to meet the bark and wood projected, in 

 much larger quantity from the opposite, or upper lip of the wound. 



I have endeavoured in a former memoir J, to explain the cause why 

 some portion of growth takes place below incisions through the bark, 



* See the preceding memoirs, Nos. II. IV. and V. 



f During the circulation of the sap through the leaves, a transparent fluid is emitted, in the 

 night, from pores situated on their edges, and on evaporating this liquid obtained from very 

 uxuriant plants of the vine I found a very large residuum to remain, which was similar in 

 external appearance to carbonate of lime. It must however have been a very different substance 

 from the very large portion which the water held in solution. I do not know that this sub- 

 stance has been analysed or observed by any naturalist. 



I See above, No. III. 



