Their feet
have to be soft and padded to enable them to run over the sand with
ease; and hard horny patches must protect their knees and all other
portions of the body liable to touch the sweltering surface when they
lie down to rest themselves. Finally, they can all endure thirst for
long periods together; and the camel, the most inveterate
desert-haunter of the trio, is even provided with a special stomach to
take in water for several days at a stretch, besides having a peculiarly
tough skin in which perspiration is reduced to a minimum. He carries his
own water-supply internally, and wastes as little of it by the way as
possible.
What the camel is among animals that is the cactus among plants--the
most confirmed and specialised of desert-haunting organisms. It has been
wholly developed in, by, and for the desert. I don't mean merely to say
that cactuses resemble camels because they are clumsy, ungainly,
awkward, and paradoxical; that would be a point of view almost as far
beneath the dignity of science (which in spite of occasional lapses into
the sin of levity I endeavour as a rule piously to uphold) as the old
and fallacious reason 'because there's a B in both.' But cactuses, like
camels, take in their water supply whenever they can get it, and never
waste any of it on the way by needless evaporation. As they form the
perfect central type of desert vegetation, and are also familiar plants
to everyone, they may be taken as a good illustrative example of the
effect that desert conditions inevitably produce upon vegetable
evolution.
Pages:
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423