the Radicle and Germen of Seeds. 105 
is impelled there by centrifugal force, as it is attracted by 
gravitation to its under side, when the seed germinates at 
rest. 
This increased elongation of the fibres and vessels of the 
under side is not confined to the germens, nor even to the 
annual shoots of trees, but occurs and produces the most ex- 
tensive effects in the subsequent growth of their trunks and 
branches. The immediate effect of gravitation is certainly to 
occasion the further depression of every branch, which extends 
horizontally from the trunk of the tree ; and, when a young 
tree inclines to either side, to increase that inclination : but it 
at the same time, attracts the sap to the under side, and thus 
occasions an increased longitudinal extension of the substance 
of the new wood on that side.* The depression of the lateral 
branch is thus prevented ; and it is even enabled to raise itself 
above its natural level, when the branches above it are 
removed ; and the young tree, by the same means, becomes 
more upright, in direct opposition to the immediate action of 
gravitation : nature, as usual, executing the most important 
operations by the most simple means. 
I could adduce many more facts in support of the preceding 
deductions, but those I have stated, I conceive to be suffi- 
ciently conclusive. It has however been objected by Du 
Hamel, (and the greatest deference is always due to his 
opinions,) that gravitation could have little inffuence on 
the direction of the germen, were it in the first instance 
protruded, or were it subsequently inverted, and made to 
* This effect does not appear to be produced in what are called weeping trees ; 
the cause of which I have endeavoured to point out in a former Memoir. Phil. 
Trans. 1804. 
MDCCCVI. 
P 
