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On the Direction of the Radicle and 
Germen, during the Vegetation of 
ae By Thomas Andrew Knight, 
gq: F.R.S. Ina Letter to the 
Rake Honourable Sir Joseph 
Banks, K. B. P. B.S. 
‘(FROM THE PHILOSOPHICAL TRANS- 
, ACTIONS FOR A. p. 1806.) 
oy 
Read, Jan. 9, 1806. 
_My dear sir, 
T can scarcely have escaped the 
notice of the most inattentive 
_ observer of vegetation, that in what- 
ever position a seed is placed to ger- 
_ minate, its radicle invariably makes 
an effort to descend towards the 
centre of the earth, whilst the elon. 
"gated germen takes a precisely op- 
"posite direction ; and it has been 
e proved by Du Hamel, that if a seed, 
_ during Haecraination, be frequently 
inverted, the points, both of the 
_ radicle and germen, will return to 
the first direction. Some naturalists 
have supposed these opposite ef- 
fects to be produced by gravitation ; 
and it is not difficult to conceive 
‘that the same agent, by operating 
on bodies so differently organized 
_as the radicle and germen of plants 
are, may occasion the one to de- 
scend and the other to ascend. 
The hypothesis of these natu- 
-ralists does not, however, appear 
to have been much strengthened 4 
Ry. 
F 
NATURAL HISTORY 
any facts they were able to adduce 
in support of it, nor much weaken- 
ed by the arguments of their oppo- 
nents; and, therefore, as the phe- 
nomena observable during the con- 
version of a seed into a plant, are 
amongst the most interesting that 
occur in vegetation, I commenced 
the experiments, an account of 
which i have now the honour to 
request you to lay before the royal 
society. 
1 conceived that if gravitation 
were the cause of the descent of the 
radicle, and of the ascent of. the 
germen, it must act either by its im. 
mediate influence on the vegetable 
fibres and vessels, during their for- 
mation, or on the motion and con. 
sequent distribution of the true sap 
afforded by the cotyledons: and as 
gravitation could produce these ef. 
fects only whilst the seed remained 
at rest, and in the same position 
relative to the attraction of the 
earth, I imagined that its operation 
would become suspended by con- 
stant and rapid change of the posi- 
tion of the germinating seed, and 
that it might be counteracted by the 
agency of centrifugal force. 
Having astrong rill of water pass- 
ing through my garden, I constructed 
a small wheel, similar to those used 
for grinding corn, adapting another 
wheel of ditfereat construction, and 
formed 
