108 Mr. Knight on the Direction of Radicles , &c. 
much has been written, will possibly be adduced as an excep*- 
tion ; but having attentively examined at least 20,000 trees 
of this species, many of which had grown in some of the 
deepest and most favourable soils of England, and never 
having found a single tree possessing a tap root, I must be 
allowed to doubt that one ever existed. 
As trees possess the power to turn the upper surfaces of 
their leaves, and the points of their shoots to the light, and 
their tendrils in any direction to attach themselves to conti- 
guous objects, it may be suspected that their lateral roots are 
by some means directed to any soil in their vicinity which is 
best calculated to nourish the plant, to which they belong ; 
and it is well known that much the greater part of the roots 
of an aquatic plant, which has grown in a dry soil, on the 
margin of a lake or river, have been found to point to the 
water ; whilst those of another species of tree which thrives 
best in a dry soil, have been ascertained to take an opposite 
direction : but the result of some experiments I have made is 
not favourable to this hypothesis, and I am rather inclined to 
believe that the roots disperse themselves in every direction, 
and only become most numerous where they find most em- 
ployment, and a soil best adapted to the species of plant. 
My experiments have not, however, been sufficiently varied, 
or numerous, to decide this question, which I propose to 
make the subject of future investigation. 
I am, &c. 
T. A. KNIGHT. 
Elton, Nov. 22, 1805. 
