of birds, as in the burdock, cleavers, and
many other species. Others again are sticky, as in Plumbago europaea,
mistletoe, and many foreign plants.

All the seeds or seed-vessels which are adapted to be dispersed in any
of these ways are of dull protective tints, so that when they fall on
the ground they are almost indistinguishable; besides which, they are
usually small, hard, and altogether unattractive, never having any
soft, juicy pulp; while the edible seeds often bear such a small
proportion to the hard, dry envelopes or appendages, that few animals
would care to eat them.

_The Meaning of Nuts._

There is, however, another class of fruits or seeds, usually termed
nuts, in which there is a large amount of edible matter, often very
agreeable to the taste, and especially attractive and nourishing to a
large number of animals. But when eaten, the seed is destroyed and the
existence of the species endangered. It is evident, therefore, that it
is by a kind of accident that these nuts are eatable; and that they are
not intended to be eaten is shown by the special care nature seems to
have taken to conceal or to protect them. We see that all our common
nuts are green when on the tree, so as not easily to be distinguished
from the leaves; but when ripe they turn brown, so that when they fall
on to the ground they are equally indistinguishable among the dead
leaves and twigs, or on the brown earth. Then they are almost always
protected by hard coverings, as in hazel-nuts, which are concealed by
the enlarged leafy involucre, and in the large tropical brazil-nuts and
cocoa-nuts by such a hard and tough case as to be safe from almost every
animal. Others have an external bitter rind, as in the walnut; while in
the chestnuts and beech-nuts two or three fruits are enclosed in a
prickly involucre.

Notwithstanding all these precautions, nuts are largely devoured by
mammalia and birds; but as they are chiefly the product of trees or
shrubs of considerable longevity, and are generally produced in great
profusion, the perpetuation of the species is not endangered. In some
cases the devourers of nuts may aid in their dispersal, as they probably
now and then swallow the seed whole, or not sufficiently crushed to
prevent germination; while squirrels have been observed to bury nuts,
many of which are forgotten and afterwards grow in places they could not
have otherwise reached.[140] Nuts, especially the larger kinds which are
s