ining a foothold elsewhere.
Essentially tropical in type, it was provided with no means of
dispersing its seeds across the enormous expanse of intervening ocean
which separated its habitat from the sister continents.

But why are cactuses so almost universally prickly? From the grotesque
little melon-cactuses of our English hothouses to the huge and ungainly
monsters which form miles of hedgerows on Jamaican hillsides, the
members of this desert family are mostly distinguished by their
abundant spines and thorns, or by the irritating hairs which break off
in your skin if you happen to brush incautiously against them. Cactuses
are the hedgehogs of the vegetable world; their motto is _Nemo me
impune lacessit_. Many a time in the West Indies I have pushed my hand
for a second into a bit of tangled 'bush,' as the negroes call it, to
seize some rare flower or some beautiful insect, and been punished for
twenty-four hours afterwards by the stings of the almost invisible and
glass-like little cactus-needles. When you rub them they only break in
pieces, and every piece inflicts a fresh wound on the flesh where it
rankles. Some of the species have large, stout prickles; some have
clusters of irritating hairs at measured distances; and some rejoice in
both means of defence at once, scattered impartially over their entire
surface. In the prickly pear, the bundles of prickles are arranged
geometrically with great regularity in a perfect quincunx. But that is
a small consolation indeed to the reflective mind when you've stung
yourself badly with them.

The reason for this bellicose disposition on the part of the cactuses
is a tolerably easy one to guess. Fodder is rare in the desert. The
starving herbivores that find themselves from time to time belated on
the confines of such thirsty regions would seize with avidity upon any
succulent plant which offered them food and drink at once in their last
extremity. Fancy the joy with which a lost caravan, dying of hunger and
thirst in the byways of Sahara, would hail a great bed of melons,
cucumbers, and lettuces! Needless to say, however, under such
circumstances melon, cucumber, and lettuce would soon be exterminated:
they would be promptly eaten up at discretion without leaving a
descendant to represent them in the second generation. In the ceaseless
war between herbivore and plant, which is waged every day and all day
long the whole world over with far greater persistence than the war