hest possible limit. Not
content with mere defense, it is to some extent actively aggressive. The
hairs which clothe it have become filled with a poisonous, irritating
juice, and when any herbivore thrusts his tender nose into the midst of
a clump, the sharp points pierce his naked skin, the liquid gets into
his veins in the very neighborhood of the most sensitive nerves, and the
poor creature receives at once a lifelong warning against attacking
nettles in future.

The way in which so curious a device has grown up is not, it seems to
me, very difficult to guess. Many plants are armed with small sharp
hairs which act as a protection to them against the incursions of ants
and other destructive insects. These hairs are often enough more or less
glandular in structure, and therefore liable to contain various waste
products of the plant. Suppose one of these waste products in the
ancestors of the nettle to be at first slightly pungent, by accident, as
it were, then it would exercise a slightly deterrent effect upon
nettle-eating animals. The more stinging it grew, the more effectual
would the protection be; and as in each generation the least protected
plants would get eaten down, while the more protected were spared, the
tendency would be for the juice to grow more and more stinging till at
last it reached the present high point of development. It is noticeable,
too, that in our warrens and wild places, most of the plants are thus
more or less protected in one way or another from the attacks of
animals. These neglected spots are overgrown with gorse, brambles,
nettles, blackthorn, and mullein, as well as with the bitter spurges,
and the stringy inedible bracken. So, too, while in our meadows we
purposely propagate tender fodder plants, like grasses and clovers, we
find on the margins of our pastures and by our roadsides only protected
species; such as thistles, houndstongue, cuckoo-pint, charlock, nettles
(once more), and thorn bushes. The cattle or the rabbits eat down at
once all juicy and succulent plants, leaving only these nauseous or
prickly kinds, together with such stringy and innutritious weeds as
chervil, plantain, and burdock. Here we see the mechanism of natural
selection at work under our very eyes.

But the sting certainly does not exhaust the whole philosophy of the
nettle. Look, for example, at the stem and leaves. The nettle has found
its chance in life, its one fitting vacancy, among the ditches and
was