Natural History. 451 
vertical wheel, rotating rapidly, directed their radicle towards 
the circumference, and their plumula towards the centre. When 
the wheel was horizontal, the radicles affected a direction in- 
termediate between a vertical and a horizontal line, but tending 
towards the circumference; the plumula took an analogous di- 
rection, tending towards the centre. M. Dutrochet has repeat- 
ed and verified these experiments, and having extended them, 
has arrived at the following results : 
When the grains are placed at the circumference of a vertical 
wheel turning with a certain rapidity, the radicles are con- 
stantly directed towards the circumference and the plumula to- 
wards the centre. 
When the rotation is very slow, so that there is no apprecia- 
ble centrifugal force ; the radicle and the plumula are directed 
in the line of a tangent, the first advancing or going with the 
motion, the latter receding, or going in opposition to the 
motion. 
When the grains are placed at the circumference of a hori- 
zontal wheel turning with great rapidity, the radicle and plu- 
mula direct themselves in a perfectly horizontal direction, the 
first towards the circumference, and the second towards the 
centre. The more the motion is diminished, the greater the 
tendency in these parts to resume their natural direction to- 
wards the earth and the heavens. 
When the grains are placed at the centre of a vertical wheel, 
of which the axis has a very slight inclination; the radicle and 
the plumula direct themselves parallel to the axis, the first to- 
wards the descending, and the second towards the ascending, 
art. 
, When the axis is perfectly horizontal, the radicle and plumula 
direct themselves according to the tangent of the small circle 
the grain describes in turning round itself; then, as in the pre- 
ceding experiments, the radicle advances forward, the plumula 
moves backwards. 
If whilst a grain turns on itself, the axis being perfectly hori- 
zontal, it be subjected to a succession of small blows or taps 
continually in the same direction, the radicle will direct itself 
in the line of the blow; the plumula, on the contrary, will move 
in the opposite direction from the blow; by this means, these 
parts may be directed at pleasure. 
It results from all these facts, that the radicle constantly di- 
rects itself in the direction of the movement, or tendency, of 
which it feels the influence, and that the plumula as con- 
stantly directs itself in the opposite direction to that of the 
movement, or tendency, of which it feels the influence. So that 
with the radicle there is obedience to the exterior cause which 
influences it ; whilst, on the contrary, with the plumula there is 
re-action against the exterior cause which influences it. Thus 
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