1819,] Direetion of the Radicle and Germen. 259 
the effect of advancing vegetation, for they were already at their 
full growth. 
Indeed so far is the bend from being likely to oecasion an 
increased flow of sap on the under side, that it seems to me te 
be the most likely means of retarding it ; as the yessels on the un- 
der side must be too strongly compressed to afford aready passage 
for the sap, while those on the upper side occasion no obstruc- 
tion to it; and it does not in fact appear that there is any accu- 
mulation of matter deposited on the under side of horizontal or 
deflected branches; on the contrary, in examining a number 
of branches so circumstanced, particularly branches of the ash- 
tree, I have uniformly found the greatest thickness of woody 
layers to be on the upper side. 
Such are the obstacles that present themselves to Mr. Knight’s 
explanation of the phenomenon in question. But even allowing 
it to be the true one, what is it that gives occasion to the bend 
downwards? For it appears that gravitation cannot act till a 
bend in the stem takes place. Say that the bend is occasioned 
hy accident, or by the natural tendency of heayy bodies to grayi- 
tate, or by the stems being so weak and limber that it cannot 
support itself, or by the plumelet’s being deflected in the seed. 
The conditions required are given; and the cause assigned by 
Mr. Knight will produce the effect ascribed to it, if possible. But 
if I take a seed whose plumelet is not deflected, and plant it so 
as that the plumelet shall point perpendicularly downwards, why 
should it again turn up? Will it be said that it is made to turn 
up by means of the great quantity of liquid that is directed into 
it in the process of germination, as it is said that the pendant 
stem may be afterwards made toturnup? Then I reply that the 
great quantity of liquid ought, @ fortiori, to compel it to point 
downwards still, since it is acting with its full force in the very 
direction of gravitation; or, at the least, that if gravitation 
elevates the bent plumelet, or the plumelet of whatever shape, 
it ought, for the same reason, to elevate the bent radicle ; for 
{ have proved that it finds them both in precisely the same 
circumstances ; so that if Mr. Knight still persists in regarding 
gravitation as the cause that gives direction to the plant, he wall 
e compelled to look out for a new explanation of the way in 
which it acts. 
Mr. Knight now proceeds to answer objections. Du Hamel 
had said that gravitation could have but little influence in the 
direction of the plumelet, were it in the first instance protruded, 
or afterwards made to grow perpendicularly downwards. This 
is a case that Mr. Knight seems to regard as apparently hostile 
to his ees 5 and it is the case that I have just put. But 
what is his answer to the objection? Merely that having made 
many experiments on the inverted seeds of the horse-chesnut 
and the bean, he found that after a certain time the extremity of 
R2 
