120 On the inverted Action 
thesame mode of analysis, and that certain substances which 
I have separated without difficulty, could not present them- 
selves to him but after a number of experiments. But J am 
far from pretending to have made a complete analysis, and 
I shall esteem myself very fortunate if I have been able to 
present you with some facts worthy of your attention. 
XXIV. On the inverted Action of the allurnous Vessels of 
Trees. By Tuomas ANDREW Knicut, Esq. F.R.S., 
Ina Letter to the Right Honourable Sir Josern Banks, 
K. B. P.R.S* 
MY DEAR SIR, 
] HAVE engeavoured to prove, in several memoirs¢ which 
you have done me the honour to lay before the Royal So- 
ciety, that the fluid by which the various parts (that are an- 
nually added to trees, and herbaceous plants whose organiza- 
tion is similar to that of trees,) are generated, has previously 
circulated through their leaves f either in the same or pre- 
ceding season, and subsequently descended through their 
bark ; and after having repeated every experiment that oc- 
curred to me, from which I suspected an unfavourable re- 
sult, Iam 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 
Du Hamel which appears strongly to militate against my 
hypothesis; and as that circumstance probably indused Hales 
to deny altogether the existence of circulation in plants, and 
Du Hamel to speak less decisively in favour of it than he 
possibly might otherwise have done, I am anxious to recon- 
* From Philosophical Transactions for 1806. 
+ In the Phil. Trans. for 1801, [803, 1804, and 1805. 
¢ 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 evapo- 
rating this liquid, obtaimed from very luxuriant 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 evidently a very different’ 
substance, from the very large portion which the water held in solution. Ido 
not know that this substance has been analysed, or noticed by any naturalist. 
cile 
