PHILOSOPHICAL 
TRANSACTIONS. 
XL On the Causes which influence the Direction of the Growth of 
Roots. By T. A. Knight, Esq. F. R. S. in a Letter to the 
Right Hon. Sir Joseph Banks, Bart. K. B. P. R. S. 
Read March 7, 1811. 
1 have shewn, in a former communication, the effects of cen- 
trifugal force upon germinating seeds; from which I have 
inferred that the radicles are made to descend towards the 
earth, and the germs, or elongated plumules, to take the op- 
posite direction, by the influence of gravitation ; and I believe 
the facts I have stated to be sufficient to support the inferences 
I have drawn.* But the fibrous roots of plants, being much 
less succulent, though not uninfluenced in the directions they 
take by gravitation, are, to a great extent, obedient to other 
laws, and are generally found to extend themselves most 
rapidly, and to the greatest length, in whatever direction the 
soil is most favourable : whence many naturalists have been 
disposed to believe that these are guided by some degrees of 
feeling and perception, analogous to those of animal life. 
I shall proceed to state some of the facts upon which this 
* Phil. Trans. 1806, 1st Part, page 5. 
E e 
MDCCCXI. 
