Mr. Knigi-it on the Reproduction of Buds. 263 
inverted position of the branch, than on the opposite lip, which 
would not have happened had the branch continued to grow 
erect, and I have inferred that this effect was produced by sap 
which had descended by gravitation from the leaves above. 
But the branch was, as I have there stated, employed as a 
layer, and the matter which would have accumulated on the 
opposite lip of the wound had been employed in the formation 
of roots, a circumstance which at that time escaped my atten- 
tion. The effects of gravitation on the motion of the descending 
sap, and consequent growth of plants, are, I am well satisfied, 
from a great variety of experiments, very great; but it will 
be very difficult to discover any method by which the extent 
of its operation can be accurately ascertained. For the vessels 
which convey and impel* the true sap, or fluid from which 
the new wood appears to be generated, pass immediately from 
the leaf-stalk towards the root ; and though the motion of this 
fluid may be impeded by gravitation, and it be even again 
returned into the leaf, no portion of it, unless it had been ex- 
travasated, could have descended to the part from which the 
bark was taken off in the experiment I have described. I am 
not sensible that in the different Papers which I have had the 
honour to address to you, I have drawn any other inference 
which the facts, on repetition of the experiments, do not appear 
capable of supporting. 
I am, &c. 
THO s . ANDREW KNIGHT, 
Elton, 
May 12, 1805. 
■* Phil. Trans, of 1804, 
