202 
OF PLANTS. 
issuing from the seed take their respective directions, into 
whatever position the seed itself happens to be cast. If 
the seed be thrown into the wrongest possible position, 
that is, if the ends point in the ground the reverse of what 
they ought to do, everything, nevertheless, goes on right. 
The sprout, after being pushed down a little way, makes 
a bend, and turns upwards: the fibres, on the contrary, 
after shooting at first upwards, turn down. Of this extraor¬ 
dinary vegetable fact, an account has lately been attempted 
to be given: “The plumule, (it is said,) is stimulated by 
the air into action, and elongates itself when it is thus 
most excited; the radicle is stimulated by moisture, and 
elongates itself when it is thus most excited. Whence 
one of these grows upward in quest of its adapted object, 
and the other downward.”* Were this account better 
verified by experimentf than it is, it only shifts the con- 
Nature has provided the elements of germination on every part of the 
surface; water and pure air and heat are universally active, and the 
means for the preservation and multiplication of life, are at once simple 
and grand.” Sir H. Davy's Elements of Agricultural Chemistry , 
‘i. ed. p. 70.— Paxton. 
* Darwin’s Phytologia, p. 144. 
t “ Gravitation has a very important influence on the growth of plants; 
and it is rendered probable, by the experiments of Mr. Knight, that they 
owe the peculiar direction of their roots and branches almost entirely to 
its force. 
“ That gentleman fixed some seeds of the garden bean on the circum¬ 
ference of a wheel, which in one instance was placed vertically, and in 
the other horizontally, and made to revolve, by means of another wheel 
worked by water, m ^uch a manner, that the number of the revolutions 
could be regulated; the beans were supplied with moisture, and were plac¬ 
ed under circumstances favorable to germination. The great velocity 
of motion given to the wheel was such, that it performed 250 revolutions 
in a minute. It was found that in all cases the beans grew, and that the 
direction of the roots and stems was influenced by the motion of the 
wheel. When the centrifugal force was made superior to the force of 
gravitation, which was supposed to be done when the vertical wheel per¬ 
formed 150 revolutions in a minute, all the radicles, in whatever way 
they were protruded from the position of the seeds, turned their points 
outwards from the circumference of the wheel, and in their subsequent 
growth receded nearly at right angles from its axis; the germens (plum¬ 
ules) on the contrary, took the opposite direction, and in a few days their 
points all met in the centre of the wheel. 
“When the centrifugal force was made merely to modify the force of 
gravitation in the horizontal wheel, where the greatest velocity of revolu¬ 
tion was given, the radicles pointed downwards about ten degrees below, 
and the germens (plumules) as many degrees above the horizontal line of 
the wheel’s motion; and the deviation from the perpendicular was less in 
proportion, as the motion was less rapid. 
“ These facts afford a rational solution of this curious problem, respect- 
