1816.] On the upright Growth of Vegetables. 445 
put in motion, with velocities varying from 80 to 250 revolutions in 
a minute. The result was exceedingly interesting, The seeds 
which germinated on the vertical wheel had the positions of their 
radicles and germens determined altogether by the motion of the 
wheel. ‘The radicles protruded nearly straight outwards, whilst the 
germens in a few days encountered each at the centre. Extending 
beyond that point, the operating cause arrested their progress. They 
again returned, and met a second time at the centre. ‘The germi- 
nations on the horizontal wheel, again, were differently affected. 
They were left exposed to the continued action of gravitation. The 
line of their progress, therefore, was the resolution of unequal 
forces. ‘They were deflected ten degrees downwards from the plane 
of the wheel, the centrifugal force produced by 250 revolutions in 
a minute, in their circumstances, being to the force of gravitation 
as nine to one. 
These results certainly establish the general principle; for they 
exhibit the uniform and exclusive effects of gravitation. Although, 
therefore, the conviction on my mind was previously complete, 
from the view of the coincidence between the cause and the effect, 
it is with much satisfaction I refer to Mr. Knight’s experiment as 
affording the conclusive proof. 
Did we know nothing more of the structure of plants, or the 
process of vegetation, we should still be bound to receive the 
paradox that vegetables grow upwards by virtue of a force drawing 
downwards ; but we are enabled, though with much less certainty, 
to proceed somewhat further in this investigation: 
Mr. Knight has offered a theory of the mode by which gravity 
operates in producing the upright growth of vegetables ; and every 
thing which comes from such an acute mind deserves serious consi- 
deration. In the present instance, however, his theory, though, 
like all his suggestions, very ingenious, is evidently inconsistent with 
the phenomena of nature, and therefore must be erroneous. 
But I do not consider myself entitled to throw aside the opinions 
of such an accurate observer without a detailed refutation. His 
hypothesis, compressed into a short proposition, seems to be this— 
that by the common principles of gravitation the sap accumulates 
in the under side of a deflected germen ; that by this accumulation 
of the sap, and consequent increased growth of that part, the under 
side is elongated ; that this elongation turns up the point, and that 
the perpendicular growth of plants is thus effected by a series of 
‘corrections. 
Now it must be remarked, in the outset, that the leading fact on 
which Mr. Knight seems to found his opinion, viz. that the under 
side of a deflected germen does elongate, affords a very equivocal 
proof, indeed, of the inference drawn from it, that the perpendi- 
cular growth of that germen is the etfect of this elongation ; for, 
whatever be the cause of the ascent of the germen, it !s demon- 
strable that, whenever it does operate on a plant which has been 
bent to one side, the under or shortest side must elongate. It could 
