CACTUS SPINES AND PECULIARITIES
And now we will pause in our trip across Cactus Land to take up the many
peculiar features which characterize and differentiate these odd desert
plants, and to tell of those individual and unique growths, the terrible
swordlike thorns of the strange Fantastic Clan.
PECULIARITIES
Cacti are not closely related to any other family of plants, and there is
no certainty as to which group of plants they developed from. Their
immediate ancestors perhaps have disappeared in the hazy past. They
stand, therefore, alone. In this respect few other plants resemble them;
only one or two other families, for instance the Ocotillos or
Fouquieriaceæ, are in a like position.
Cacti are generally thought of as limited to North and South America and
the outlying islands. However, about eleven species of one genus,
Rhipsalis, grow, apparently native, in South Africa, Madagascar, and
Ceylon, though these are identical with the same species growing in South
America. There is a strong belief that these species were distributed in
Africa by birds eating their ripe fruit in South America and then flying
across the ocean to Africa, and there dropping the seeds, which
germinated and grew into plants on another continent. The most widely
distributed of the various groups of cacti is the prickly pear group of
the genus Opuntia. The prickly pears grow wild from Argentina through
Central America, Mexico, and the United States to British Columbia,
within four or five hundred miles of the Arctic Circle. Prickly pears may
be regarded as the advance guard of the cactus invasion of the United
States from Mexico, and there are nearly as many kinds in our country as
in Mexico. Prickly pears are most abundant in the temperate zones; the
species grow larger in tropical parts than in cooler temperate regions.
All told, there are more than twelve hundred species or kinds of cacti,
of which about two hundred twenty-five occur in the United States and the
rest in Mexico, Central America, South America and outlying islands. Of
the two hundred twenty-five species occurring in the United States, about
one hundred are native of Arizona, the premier cactus state, and nearly
two hundred grow in the four southwestern states, California, Arizona,
New Mexico, and Texas, with a few in Nevada and Utah. Arizona contains
almost one-tenth of the cacti of the entire earth. Our four southwestern
states together with Mexico constitute the great cactus area of the
world, not alone in numbers but in variety and weirdness of types,
containing many of the most peculiar and fantastic forms of these
grotesque plants.
Doubtless because the cacti are such odd, weird, fantastic growths, they
have been popular with mankind since the earliest times. To-day forty or
fifty species are known only in cultivation; and they have been under
culture so long that their native habitats and original distribution have
been forgotten, and are no longer known. This is due largely to the fact
that several very popular species have been dug up and removed from their
own haunts to cultivated lands, or planted in gardens to such an extent
that the last specimens have been taken and they no longer grow wild or
under natural conditions. This uprooting is taking place continuously,
doubtless much faster now than formerly, and in future we shall have many
additional instances to record, as it is quite likely that new species
are originating under experimentation through careful selection and
ingenious plant breeding.
[Illustration: SHORT SPINED STRAWBERRY CACTUS (Echinocereus Bonkeræ)]
A new and handsome little strawberry cactus, named in honor of Frances
Bonker for her writings depicting the beauty and charm of the desert
land.
SPINES AND FLOWERS
The spines of cacti are ever an interesting subject for study, and the
very name “cactus” is suggestive of thorns. It is generally known that
cactus spines develop from their bases and that they are impregnated with
resin or a resinlike substance, while the spines of nearly all other
plants (as for instance the plum) grow from their tips and are not
resinous in character. A young growing cactus spine has a very soft
yielding base while the tip is hard and sharp, and the sides retrorsely
barbed. Because of their resinous nature the thorns persist on the desert
long after the cactus body has disappeared, and often fragments of the
thick cuticle remain with them, still firm, sharp and translucent. Such
spines about a spot where a noble Sahuaro or Giant Cactus has fallen and
gone back to Nature as dust may persist for a long period unchanged,
without crumbling or otherwise disintegrating; this is true also of those
of the bisnaga or barrel cactus. Thorns grow on the Giant Cacti for a
hundred, even two hundred years, unalterable, sharp and hard and
dangerous. Some species of cactus have as many as three kinds of spines:
centrals, the inner thorns, usually the largest and stoutest; radials,
the outer spines; and what are termed “bristles” but are more accurately
described as “antennalike” spines. In some groups, as the bisnaga, the
spines are cross-ridged or marked transversely, with the tips smooth,
straight, or hooked. Many cactus spines are marked with brilliant
colorings, and some are transversely banded with bright variegated
“zones” of color. When held to the light they are translucent and show
beautiful colorings: red, orange, yellow, brown, and purple. Generally
cactus spines are glabrous, that is, smooth and without hairs, but the
spines of some cacti are densely fine-hairy or distinctly hairy; and this
can be seen easily with a pocket lens or the unaided eye: their
pubescence commonly produces a grayish layer overlying the true color of
the spines beneath. The thorns of Cholla differ from those of other cacti
in that they are covered with sheaths which can be removed very easily,
and then are not replaced. The significance of these sheaths is not
clear, except that they help form a barrier against the intense heat of
the sun and the burning desert sands.
We find, too, that the cacti with most pronounced thorny growth live in
the hottest parts of the desert, where the thermometer often registers
130° Fahrenheit during the long summer days and sometimes up to 150°!
Their dense layer of spines becomes a shield of lacework, protecting the
plants by cutting off over twenty per cent of the light, and reducing the
terrible heat by raising the humidity within the network of spines, which
in turn reduces evaporation from the plant. If it were not for their
thorns and sheaths cacti would be scalded by the burning temperatures of
even one summer day in the great desert amphitheater of the sun. Being
resinous, cactus thorns are very inflammable, and if ignited they all
burn to a cinder before the fire ceases, for one cluster of spines will
set others aflame and so the fire sweeps over the entire plant, rapidly
changing the beautifully colored, symmetrical and translucent spines into
ugly charred masses.
The cactus is encased in a thick cuticle which is continuous over the
whole surface of the plant, except at the numerous, small, rounded or
oval areas of growth called areolas. In the cactus all growth, of leaves,
spines, spicules, flowers, and even roots (in the case of cuttings) and
branches, takes place from these areolas, which are truly areas or
centers of growth; and if all these areolas are cut away on the stem and
its tip cut off, the plant ceases to grow and dies. Spines are generally
understood to represent branches, since they grow from the tissues of the
plant under the epidermis and not from the epidermis. The inordinate
multiplication of spines in cacti is not well understood by botanists.
Some cacti add thorns to their spine clusters in the areolas each year,
and thus in time the cluster may come to have as many as fifty or even a
hundred spines on old stems and large branches. Occasionally cactus
spines replace themselves in areolas after the former thorns have been
destroyed or burned off. The thorns of some cacti may grow as long as six
inches and even longer, and as broad as one-fourth inch at their bases.
After they complete their growth toward the close of the season and the
bases become hard and firm, they do not elongate farther nor make further
growth.
The flowers of cacti are generally large and showy and are quite
responsive to light in their opening and closing. They have many stamens,
from thirty or fifty to as many as three thousand in the Giant Cactus.
This development of stamens is rare among flowering plants, and is due to
a splitting process that takes place early in the development of the
stamens of the embryo flower. The stamens of many cacti are sensitive to
touch and when being worked by insects for pollen are constantly moving
backward and forward. Cactus flowers differ also from nearly all other
flowers in the number of sepals and petals, which is variable and
relatively large, and in the fact that their sepals and petals are not
distinct in character. Rather there is a gradual transition between the
bracts of the ovary, if such are present, and the sepals; and likewise a
gradual gradation in form, color, and size between the sepals and petals.
There are usually several whorls or circles of petals in the flower;
commonly such flowers are spoken of as being double.