1816.] On the upright Growth of Vegetables, 453 
becomes us, therefore, to examine minutely all the circums tances 
connected with the action of this centrifugal force, as they regard 
the parts of the plant on which it acts, and the manner in which 
its force is exerted. 
1. The process of evaporation goes on in every part of the plant, 
though chiefly in the tender parts, the young shoot, and the leaves, 
The bud, indeed, almost always protrudes the leaves first, and in 
many plants the leaves continue for a long time to envelope the 
stem. It must, therefore, be held that almost every particle of a 
plant, and particularly those particles at the top of the plumula, 
which are most soft and pliant, are exposed to the action of that 
centrifugal force, which is produced by the conversion of the par- 
ticles of water attached to them, into gaseous vapour or steam; and 
therefore the effect does not depend altogether on the quantity 
evaporated in a given time, but on the quantity adhering to the 
plant, and the existing temperature by which the buoyancy of the 
gas is regulated. 
2. We must contemplate each integrant particle of a plant to 
which a particle of gas adheres, as supported by its cohesion to the 
contiguous particles by which it is surrounded; so that, independ- 
ently of any buoyancy derived from its connexion with the gas, it 
syvould hang, not downwards, but in a direction more or less in- 
clined, according to the force with which it coheres to the con- 
tiguous particles. To the particles, in these circumstances, we 
have to apply the influence of the ascending vapour. Possessed of 
considerable buoyancy, or centrifugal force itself, the particle of 
vapour, whilst it continues to adhere to the particle of the plant, 
Must communicate to it a portion of that buoyancy. ’ 
But, 3dly, The operation of this force in raising the particle of” 
the plant to an upright position, must have the advantage of a lever 
power. he cohesion of the particles of the plant may be resolved 
into a succession of attractions from the centre to the surface of the 
stem. Each radius of this circle may be considered as a lever, 
having the central point as a fulcrum, or rather each particle in 
succession, ray be considered as thus acted upon, the fulcrum of 
each being that point where the cohesive power is greatest, and 
which must always be the point nearest the centre. Even in the 
leaves something of this effect of cohesion will be found; for the 
footstalk of the leaf serves as its support, and as a medium by which 
any buoyancy produced in the leaf is immediately communicated to 
the twig or the stem. 
Looking to each particle as thus acted upon, by a force which, 
though weak, is incessant in its operation; and recollecting what a 
small force is required to give perpendicularity to even a consider- 
able weight, when supported at no great angle from the perpen- 
dicular, we have no reason to conclude that the cause now assigned 
must under any circumstances of the plant be inadequate to the 
effect. It is evident from Mr. Knight's experiment with the 
horizontal wheel that the circumstance of the centrifugal force 
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