[ I2 7 ] 
Mr. Du-Hamel, in his Phyfiologyof Trees, con- 
tents himfelf with relating what has been faid 
for or againft this opinion ; but, though he fuf- 
ficiently hints that he does not believe it true, he 
determines nothing about it. The friends of the 
circulation in plants have never been able to find 
in them any thing analogous to that powerful 
organ, which is the promoter of it in animals ; 
for want of fuch an organ, they were forced to 
imagine valves and paps in the lymphatick veffels 
of plants, by means of which the liquors once 
introduced into the fap veffels were fuppofed to 
be hindered from going back; but, unfortunately, 
no body has ever been able to difcover thele valves 
and paps, fo different from the limple contrivan- 
ces, by which nature is ufed to arrive at her ends. 
An experiment, which I made, and of which 
I propofe giving an account in this paper, throws 
a great light upon this queftion, as well as upon 
feveral others ; and the conclufions deducible from 
it appear to me decifive. 
On the 12th of January, I placed feveral darn bs 
in pots againft the windows of my hot-houfe, 
fome within the houfe, and others without it. 
Through holes made for this purpofe in the panes 
of glafs, I palTed a branch of each of the fhrubs, 
fo that thole on the infide had a branch without, 
and thofe on the outfide one within ; after this, 
I took care that the holes fhould be exactly clofed 
and luted. This inverfe experiment, I thought, 
if followed clofely, could not fail affording fuf- 
ficient points of comparifon, to trace out the dif- 
ferences, by the obfervation of the effe&s. 
