different from that of branches. It is not a grasp, or clutch by
contraction, as that of a bird's claw, or of the small branches we call
'tendrils' in climbing plants. It is a dead, clumsy, but inevitable grasp,
by swelling, _after_ contortion. For there is this main difference between
a branch and root, that a branch cannot grow vividly but in certain
directions and relations to its neighbour branches; but a root can grow
wherever there is earth, and can turn in any direction to avoid an
obstacle.[14]

6. In thus contriving access for itself where it chooses, a root contorts
itself into more serpent-like writhing than branches can; and when it has
once coiled partly round a rock, or stone, it grasps it tight, necessarily,
merely by swelling. Now a root has force enough sometimes to split rocks,
but not to crush them; so it is compelled to grasp by _flattening_ as it
thickens; and, as it must have room somewhere, it alters its own shape as
if it were made of {30} dough, and holds the rock, not in a claw, but in a
wooden cast or mould, adhering to its surface. And thus it not only finds
its anchorage in the rock, but binds the rocks of its anchorage with a
constrictor cable.

7. Hence--and this is a most important secondary function--roots bind
together the ragged edges of rocks as a hem does the torn edge of a dress:
they literally stitch the stones together; so that, while it is always
dangerous to pass under a treeless edge of overhanging crag, as soon as it
has become beautiful with trees, it is safe also. The rending power of
roots on rocks has been greatly overrated. Capillary attraction in a willow
wand will indeed split granite, and swelling roots sometimes heave
considerable masses aside, but on the whole, roots, small and great, bind,
and do not rend.[15] The surfaces of mountains are dissolved and
disordered, by rain, and frost, and chemical decomposition, into mere heaps
of loose stones on their desolate summits; but, where the forests grow,
soil accumulates and disintegration ceases. And by cutting down forests on
great mountain slopes, not only is the climate destroyed, but the danger of
superficial landslip fearfully increased.

8. The second function of roots is to gather for the plant the nourishment
it needs from the ground. This is {31} partly water, mixed with some kinds
of air (ammonia, etc.,) but the plant can get both water and ammonia from
the atmosphere; and, I believe, for the most part does