t_ upon the mountain ranges; whilst palms
flourish in certain places as high as 8,000 feet above sea-level; and
the extraordinary cactus forms, which in Mexico are found in their
greatest development, grow both on the high mountain slopes and the
tropic lowland plains. Especially will the traveller in Mexico be
struck by the imposing _organo_ cactus. This extraordinary growth, in
form like a series of organ pipes, from which it takes its name, or
like a huge branching candelabra, arising from a single stem, is a
marked feature of the landscape. A few strokes of a machete, severing
the stem of one of these great succulent plants, will bring down the
whole structure, weighing many tons. The cactus, especially upon the
high, arid deserts of the plateau, is a striking example of a plant
contending with the conditions of its environment in the struggle for
life. Cacti are veritable cisterns of water, stored up against long
periods of absolute drought, so that they may be able to perform their
function of flowering. The _organo_ and other cacti consist of great
masses of juicy green cells; and to protect the scarce commodity of
water which they have collected for their own use from predatory desert
beasts and birds, Nature has armed them at every point with an
appalling armour of thorns, or spikes, sharp as steel, and due to these
matters of offence and defence the cactus is enabled to flourish in
sterile places where absolutely no other vegetation could exist.
Nowhere are these conditions so marked as upon the upper reaches of the
high plateau of Mexico, and the variety of the cacti is most
interesting. Among the cactus species are some which are of
value--great value--to the human inhabitants. Chief of these is the
_maguey_ (_Agave americana_), which is indeed one of the staple
resources of the country, with a varied use, as described in the pages
dealing with agriculture. The _nopat_, or prickly-pear, is a useful
plant, yielding a succulent fruit--the _tunas_--and is also the habitat
of the cochineal.

[Illustration: A ROAD IN THE TEMPERATE ZONE, WITH PALMS AND
VEGETATION.]

The tropical region--the _tierra caliente_--is generally covered, as
before described, with a profuse floral and arboreal vegetation, whilst
the other climatic belts display their own peculiar plant and tree
life. Throughout the country generally, a large number of species of
timber and plants exist in an uncultivated state, of commercial value,
and