930 
successively added to ity point: .the 
germen, on the contrary, elongates 
by a general extensicn of its parts 
previously organized ; and its ves- 
sels and fibres appear to. extend 
themseves in proportion to the 
quantity of nutriment they receive. 
If the motion and consequent distri- 
bution of the true sap be infuenced 
by gravitation, it follows, that when 
the germen at its first emission, or 
subsequently, deviates from a per- 
pendicular direction, the sap must 
accumulate on its under side; and 
I have found, in a great variety of 
experiments on the seeds of the 
horse chesnut, the bean, and other 
plants, when vegetating at rest, that 
the vessels and fibres on the under 
side of the germen, invariably elon- 
gate much more fapidly than those 
on its upper side; and thence it 
follows, that the point of the germen 
must always turn upwards; and it 
has been proved that a similar in- 
crease of growth takes place on the 
external side of the germen, whdir the 
sap is impelled there by centrifugal 
force, as it is attracted by gravita- 
tion to its under side, when the seed 
germinates at rest. 
This increased elongation of the 
fibres and vessels of the under side, 
is not cunfined to the germens, nor 
even to the annual shoots of trees, 
but occurs and produces the most 
extensive 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 at the same 
time attracts the sap to the under 
side, and thus occasions an in- 
creased longitudinal extension of the 
ANNUAL REGISTER, 1806. 
substance of the new wood on that. 
side.. The depression of the lateral 
branch is thus prevented, andit is § 
even enabled to raise itself above its - 
natural Jevel, when the branches 
above it are removed ; and the young § 
tree, by the seme means, becomes — 
more upright, in direct opposition to 
the immediate action of gravitation 5: 
nature, as usual, exccuting ihe most — 
important operations by the most 9 
simple means, 
1 could adduce many more facts 
in support of the preceding deduc- 
tions, but those I have stated, I 
conceive to be sufficiently cual’ 
sive. It has, however, been objected 
by Du Hamel (and the greatest de- 
ference is always due to his opinions) 
that gravitauion could have little 
influence on the direction of the ger- 
men, were it in the first. instance 
protruded, or were it subsequently 
inverted, and made to point perpen- 
dicularly downwards. To enable 
myself to answer this objection, I 
made many experiments on, seeds of 
the horse chesnut, and of the bean, 
in the box I have already described, 
and as the seeds there were suspend- 
ed out of the earth, I could regu- 
larly watch the progress of every ef- 
fort made by the radicle and ger- 
men, to change their positions. The 
extremity of the radicle of the bean, 
when made to point perpendicularly 
upwards, generally formed a consi- 
derable curvature within three or 
four hours, when the weather was 
warm. The germen was moreslug- 
gish ; but it rarely or never failed to 
change its direction in the course of 
twenty-four hours; and all my ef- 
forts to make it grow downwards, by 
slightly changing its direction, were 
invariably abortive. 
Another, and apparently a more 
weighty, objection, to the preceding 
hypothesis, 
