454 On the upright Growth of Vegetables. [Junz, 
being directed only to particles maintained in certain positions by 
other causes, is very material to the present question. ‘The force to 
and from thé centre produced by the revolutions of the wheel would 
not have been sufficient to have sustained one twentieth part of the 
weight of the plants, either roots or germens ; but these being sup- 
ported otherwise, by their coherence to the parts resting on the 
wheel, even when the shoots at both ends far outstretched the 
limits of immediate support, the forces generated by the motion 
were sufficient to sustain the protrusions. It is not to be doubted 
that the controuling force in that experiment was that produced by 
the circular motion, which so distinctly arranged the parts of the 
plants in that position, which corresponded with their respective 
gravities. But it must be recollected that one effect of the revolu- 
tions of the wheel was to create a little atmosphere for itself, all the 
parts of which would be affected in their centripetal and centifugal 
forces. The direction of the buoyant gases, therefore, and the 
effects produced by them, would share the common lot, and have 
their tendency to ascend or descend in lines perpendicular to the 
centre of the wheel. 
Another instance of the perpendicular elevation of heavy bodies 
by a force insufficient to sustain a single particle of these bodies, 
when applied to it in an individual isolated state, may be found in the 
tides. ‘The moon’s attraction is altogether inadequate to counter- 
balance the gravity of a particle of water, or to prevent its falling 
to the ground, yet, when it is so applied that one particle rests 
upon, and to a certain extent is thus supported by other particles, 
the attraction of the moon is found to be sufficient to sustain a 
column of water 10 feet high. Whilst we thus see the moon’s 
attraction, which is not to be compared to the buoyancy of gaseous 
vapour, producing an effect which in the aggregate excites our 
wonder and admiration, is it too much to believe that, by commu- 
nicating a part of its buoyancy to the individual particles to which 
it adheres, the constant evaporation which proceeds from a plant 
gives to it the tendency to perpendicularity. 
Although I have thus ventured to suggest a principle for the 
solution of the question why vegetables grow upward, I am far 
from aflirming that my opinion has been established by proof. This 
much, however, appears demonstrable, that evaporation goes on in 
all living plants with a never-ceasing activity, and that evaporation 
must, from its nature, communicate buoyancy, or a tendency to 
perpendicular growth. This buoyancy is the effect of that law of 
resisted attraction which produces the ascent of a balloon, the rise 
of water in a pump, and, asI have before stated, the antilunar 
tide. It is, indeed, the only cause known in nature which produces 
a direct centrifugal force, as the simple attraction on which it de- 
pends is the only known cause which produces a direct descent 
towards the centre. Whilst, therefore, I admit that much light 
must be thrown on this subject before we can have an accurate 
knowledge of the precise mode in which perpendicularity is pro- 
pueatigeteepiais 
