Chap. III.] DOWNWARD GROWTH OF THE ROOTS. 
89 
The root has as strong a first tendency down- 
ward as the stem has upward, though it puzzles 
our philosophy to account for either. The first 
downward tendency of the root is, however, 
soon counteracted by circumstances, such as the 
necessity of atmospheric aeration, the goodness 
of upper compared with lower soils, the inter¬ 
vention of rocks, chalk, &c.; and the root is 
found to grow horizontally, or sloping upward 
or downward, according to the inclination of the 
ground. I consider the idea of the tap-root of 
the oak (except as a seedling) to be a vulgar 
error. I have never seen any trace of a root at 
any great distance from the surface of the 
ground ; nor do the stumps of oaks, when grubbed, 
show any symptom of a tap-root more than 
other trees. But the question of the existence 
of tap-roots in large oaks or other timber-trees 
should not be argued as a matter of opinion, 
but proved as a matter of fact. The negative, 
indeed, cannot be proved. I could produce any 
required number of oaks without the tap-root, 
but this would not prove that others were 
without it. Let those who assert the affirmative 
produce one instance. 
The celebrated Duhamel, wishing to protect 
his field from robbery from the roots of a row 
By what agency 
is the head di¬ 
rected upward 
and the root 
downward ? 
