1819.] Direction of the Radicle and Germen. 253 
mens more upright; 80 revolutions in the minute giving an 
elevation and depression to the stem and root respectively 
of 45°.* 
From the foregoing experiments, Mr. Knight infers, “ that the 
radicles of germinating seeds are made to descend, and their 
germens to ascend, by some external cause, and not by any 
power inherent in vegetable life; and that there is but little 
reason to doubt that gravitation is the principal, if not the only 
agent employed in this case by nature.” + 
With regard to the first experiment, it may be remarked, that 
the anticipated objection is not quite so slight as Mr. Knight 
seems to have imagined ; for as the radicles were, at least dur- 
ing the one-half of their circumvolution, in their natural position, 
or nearly so, while the artificial centrifugal force was operating 
rather in conjunction with gravitation, or in the direction in 
which radicles naturally grow, so as to do more than counter- 
balance its effect in the other half of the circumvolution, in 
which the force of gravitation was opposed to it, it may be said, 
that there is no new case put from which any inference can be 
drawn ; and the moment the stems passed the centre, it was to 
them the same thing as growing downwards, which it is known 
that they cannot do. But the experiment seems to me to be 
liable to a much more serious objection than that which Mr. 
Knight had anticipated ; for, as in this case the influence of 
gravitation was conceived to be wholly suspended, and the 
radicles subjected to the agency of the centrifugal force alone, 
they ought surely to have been protruded in the direction of that 
force. Now the direction of the centrifugal force in question 
must of necessity have been oblique, as being the simple effect 
of circular motion ; and not the reverse of that of gravitation, 
hike an arrow shot from a bow perpendicularly upwards. Why 
then were the radicles protruded at right angles to the axis of 
the wheel? If one of the beans had by any accident lost its hold, 
would it have been thrown off from the circumference of the 
wheel in that direction ? Unquestionably not. It would have 
been thrown off in the direction of a tangent to the orbit which 
it was describing ; and in this direction also the radicle ought to - 
have been elongated, the direction of the plumelet being the 
reverse. 
The second experiment is thought to be the most decisive, 
and we may fairly allow it to be the most plausible of the two; 
though the account that is given of it by Mr. Knight leaves a 
desideratum that greatly diminishes its importance. We are 
told that the radicles were protruded outwards and downwards 
at about 10° below, and the germens inwards and upwards at 
about 10° above the plane of the wheel’s orbit; but we are not 
told whether this approach or recession was in the plane of the 
* Phil. Trans, 1806. Part I. p. 102, 103. + Ibid. 103. 
