11.2 
UPWARD GROWTH OF THE HEAD, AND [Part II. 
That the growth 
of the head and 
root is directed 
by gravity dis¬ 
puted. 
headlong down the contrary current of centri¬ 
fugal force. 
Sir Humphrey Davy remarks on this expe¬ 
riment :— 1u These facts afford a rational solution 
of this curious problem, respecting which dif¬ 
ferent philosophers have given such different 
opinions: some referring it to the nature of the 
sap, as De la Hire; others, as Darwin, to the 
living powers of the plant, and the stimulus of 
air upon the leaves, and of moisture upon the 
roots. The effect is now shown to be connected 
with mechanical causes ; and there seems no 
other power in nature to which it can with pro¬ 
priety be referred but gravity, which acts uni¬ 
versally, and which must tend to dispose the 
parts to take a uniform direction.” 
I honour and envy the mind which, like Mr. 
Knight’s, could foresee the probability of the 
marvellous result of this beautiful experiment; 
and, if it is allowable at all jurare in verba 
magistri , where is the master whose word we 
would take sooner than Sir Humphrey’s ? But 
surely our great philosopher is here too easily 
satisfied, at least if he means (as I understand 
him) that the direction of the growth of plants 
in general is caused by gravity. I cannot think, 
myself, that the direction of any of their growth 
