444 On the upright Growth of Vegetables. [JuNE, 
excluded from light, is still perpendicular, light cannot be the cause 
of their perpendicularity. 
We do not, indeed, see every vegetable mathematically perpen- 
dicular; they are bent and twisted in every direction. But these 
deviations, it must be scarcely necessary to observe, are obviously 
the effects of adventitious circumstances; and it is presumed that 
it will be readily admitted that, by the general law of their nature, 
all vegetables grow upright. 
It is evident that the agent which produces this universal feature 
cannot be an accidental principle, nor one dependant on any cir- 
cumstance unconnected with the general structure of the plant; 
for, were this the case, the appearances would be discordant and 
contradictory. Neither can we resort for the cause to the simple 
fiat of the Almighty; for in that case the phenomena would be 
unvaried and unvariable, whereas we know that they may be varied 
at pleasure.* The cause, therefore, must be found in some agency 
connected with the process of vegetation; and the inquiry, to be 
successful, must be conducted by the principles of sound philo- 
sophy. 
In looking for the cause of a universal effect, we must direct our 
attention to agents of universal operation ; and when we perceive a 
universal coincidence between a cause and an effect, although we 
do not thereby obtain complete proof that the one is the cause of 
the other, we undoubtedly obtain that presumptive evidence, which 
requires only the addition of circumstances, by which we can un- 
derstand how the one may be the cause of the other, to satisfy us 
that they do really stand to each other in that relation. It was under 
the influence of such views, and under the conviction that the 
general law which determines the perpendicular growth of vege- 
tables could be connected only with a universal principle acting 
with a centrifugal force, that upwards of twelvet years ago it 
occurred to me that this coincidence was only to be found in gravi- 
tation. 
The same conclusion was about two years afterwards deduced by 
Mr. Knight from a set of most ingenious and satisfactory experi- 
ments. One of these experiments, wiich of itself carries con~ 
viction, and to which I must afterwards refer, was the following :— 
Having constructed a variety of wheels, Mr. Knight fixed to their 
external circumferences a number of seeds of the garden bean, 
which had been soaked in water, and prepared for germination. 
‘These wheels, some in a vertical, and others in a horizontal, posi- 
tion, he connected with a water-wheel, by which the whole were 
* Mr. Keith, in a paper lately yead to the Linnewan Society, in despair of 
finding an intelligible cause, ascribes the ascent of the plumula, and descent of 
theradicle, to instinct. This solntion is palpably inadmissible. 
+ Being then a pupil of Dr, Coventry, in his agricultural class, 1 communi- 
cated to him my opinion, illustrated by reference to the direction that would be. 
given by gravitation to un icicle of hydrogen. 
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