CIRCULATION OF THE SAf. 5[ 



season, and subsequently descended 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 1 have advanced. 



There is, however, one circumstance stated by Hales and Apparent ob- 

 Du Hamel, which appears strongly to militate against i^^X fact'^^"/'^'^ * 

 hypothesis ; and as that circumstance probably induced Hales Hales and 

 to deny altogether the existence of circulation m plants, and ^^ Hamel. 

 Du Hamel to speak less decisively in favour of it than he pos- 

 sibly might otherwise have done, I am anxious to reconcile 

 the statements of these great naturalists, (which I acknowledge 

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

 have on former occasions coramuicated to you. 



Both Hales and Du Hamel have proved, that when two jhst the stem. 

 circular incisions through the bark, round the stem of a tree, below au an- 

 are made at a small distance from each other, and when the o"bLk"lives° 

 bark between these incisions is wholly taken away, that por- and grows, 

 tion of the stem which is below the incisions through the bark ^^o"S^ ^^^«- 

 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 {bourrelet) 

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

 makes some slight advances to meet the bark and wood pro- 

 jected, in much large quantity, from the opposite, or upper lip 

 of the wound. 



I have endeavoured, in a former Memoir,* to explain the Explanation of 

 cause why some portion of growth takes place belo v inci' this fact. 

 sions through the bark, by supposing that a small part of the 

 true sap, descending from the leaves, escapes downwards 

 through the porous substance of the alburnum. Several facts 

 stated by Hales seems favourable to this supposition ; and the 

 existence of a power in the alburnum to carry the sap in 

 different directions, is proved in the growth of inverted cut- 

 tings of different species of trees.f But I have derived so 



to remain, which was similar in external appearance to carbonate 

 of lime. It must, however, have been evideutly a very different 

 substance from the very large portion, which the water held in 

 solution. I do not know that this substance has been analyzed, 

 Qr noticed by any naturalist. 



* Phil. Trans, for J 803. f Ibid, for 1304. 



