I often wonder what mood of Nature this world of cacti which we run
against in the great Southwest expresses. Certainly something savage and
merciless. To stab and stab again suits her humor. How well she tempers
her daggers and bayonets! How hard and smooth and sharp they are! How
they contrast with the thick, succulent stalks and leaves which bear
them! It is a desert mood; heat and drought appear to be the exciting
causes. The scarcity of water seems to stimulate Nature to store up
water in vegetable tissues, just as it stimulates men to build great
dams and reservoirs. These giant cacti are reservoirs of water. But why
spines and prickles and cruel bayonets? They certainly cannot be for
protection or defense; the grass and other vegetation upon which the
grazing animals feed are not armed with spines.
If the cacti were created that grazing animals in the desert might have
something to feed upon, as our fathers' way of looking at things might
lead us to believe, why was that benevolent plan frustrated by the armor
of needles and spines?
Nature reaches her hungry and thirsty creatures this broad, mittened
hand like a cruel joke. It smites like a serpent and stings like a
scorpion. The strange, many-colored, fascinating desert! Beware! Agonies
are one of her garments.
All we can say about it is that Nature has her prickly side which
drought and heat aggravate. In the North our thistles and thorns and
spines are a milder expression of this mood. The spines on the
blackberry-bush tend against its propagation for the same reason. Among
our wild gooseberries, there are smooth and prickly varieties, and one
succeeds about as well as the other. Apple-and pear-trees in rough or
barren places that have a severe struggle for life, often develop sharp,
thorny branches. It is a struggle of some kind which begets something
like ill-temper in vegetation--heat and drought in the desert, and
browsing animals and poor soil in the temperate zones. The devil's club
in Alaska is one mass of spines; why, I know not. It must just be
original sin. Our raspberries have prickles on their stalks, but the
large, purple-flowering variety is smooth-stemmed.
Mr. John C. Van Dyke in his work on the desert expresses the belief that
thorns and spines are given to the desert plants for protection; and
that if no animal were there that would eat them, they would not have
these defenses. But I believe if there had never been a browsing animal
in the desert the cacti would have had their thorns just the same.
Nature certainly arms her animal forms against one another. We know the
quills of the porcupine are for defense, and that the skunk carries a
weapon that its enemies dread, but I do not believe that any plant form
is armed against any creature whose proper food it might become. Cacti
carry formidable weapons in the shape of spines and thorns, but the
desert conditions where they are found, heat and aridity, are no doubt
their primary cause. The conditions are fierce and the living forms are
fierce.
We cannot be dogmatic about Nature. From our point of view she often
seems partial and inconsistent. But I would just as soon think that
Nature made the adobe soil in the arid regions that the human dwellers
there might have material at hand with which to construct a shelter, as
that she gives spines and daggers to any of the vegetable forms to
secure their safety. One may confute Mr. Van Dyke out of his own mouth.
He says:
Remove the danger which threatened the extinction of a
family, and immediately Nature removes the defensive
armor. On the desert, for instance, the yucca has a thorn
like a point of steel. Follow it from the desert to the
high tropical table-lands of Mexico where there is plenty
of soil and moisture, plenty of chance for yuccas to
thrive, and you will find it turned into a tree and the
thorn merely a dull blade-ending. Follow the sahuaro and
the pitahaya into the tropics again, and with their
cousin, the organ cactus, you will find them growing a
soft thorn that would hardly penetrate clothing.
But are they not just as much exposed to browsing animals in the high
table-lands as in the desert, if not more so?
Mr. Van Dyke asserts that Nature is more solicitous about the species
than about the individual. She is no more solicitous about the one than
the other. The same conditions apply to all. But the species are
numerous; a dozen units may be devoured while a thousand remain. A
general will sacrifice many soldiers to save his army, he will sacrifice
one man to save ten, but Nature's ways are entirely different. Both
contending armies are hers, and she is equally solicitous about both.
She wants the cacti to survive, and she wants the desert animals to
survive, and she favors both equally. All she asks of them is that they
breed and multiply endlessly. Notwithstanding, according to Van Dyke,
Nature has taken such pains to protect her desert plants, he yet
confesses that, although it seems almost incredible, it is nevertheless
true that "deer and desert cattle will eat the cholla--fruit, stem, and
trunk--though it bristle with spines that will draw blood from the human
hand at the slightest touch."
This question of spines and thorns in vegetation is a baffling one
because Nature's ways are so unlike our ways. Darwin failed utterly in
his theory of the origin of species, because he proceeded upon the idea
that Nature selects as man selects. You cannot put Nature into a
formula.
Behold how every branch and twig of our red thorn bristles with cruel
daggers! But if they are designed to keep away bird or beast from eating
its fruit, see how that would defeat the tree's own ends! If no creature
ate its little red apples and thus scattered its seeds, the fruit would
rot on the ground beneath the branches, and the tribe of red thorns
would not increase. And increase alone is Nature's end.
It is safe to say, as a general statement, that the animal kingdom is
full of design. Every part and organ of our bodies has its purpose which
serves the well-being of the whole. I do not recall any character of
bird or beast, fish or insect, that does not show purpose, but in the
plant world Nature seems to allow herself more freedom, or does not work
on so economical a plan. What purpose do the spines on the prickly ash
serve? or on the thistles? or on the blackberry, raspberry, gooseberry
bushes? or the rose? Our purple-flowering raspberry has no prickles, and
thrives as well as any. The spines on the blackberry and raspberry do
not save them from browsing cattle, nor their fruit from the birds. In
fact, as I have said, the service of the birds is needed to sow their
seeds. The devil's club of Alaska is untouchable, it is so encased in a
spiny armor; but what purpose the armor serves is a mystery. We know
that hard conditions of soil and climate will bring thorns on seedling
pear-trees and plum-trees, but we cannot know why.
The yucca or Spanish bayonet and the century-plant, or American aloe
(_Agave americana_), are thorny and spiny; they are also very woody and
fibrous; yet nothing eats them or could eat them. They are no more
edible than cordwood or hemp ropes. This fact alone settles the defense
question about spines.