No part of the world can be truly understood without a knowledge of its
garment of vegetation, for this determines not only the nature of the
animal inhabitants but also the occupations of the majority of
human beings. Although the soil has much to do with the character of
vegetation, climate has infinitely more. It is temperature which causes
the moss and lichens of the barren tundras in the far north to be
replaced by orchids, twining vines, and mahogany trees near the equator.
It is rainfall which determines that vigorous forests shall grow in the
Appalachians in latitudes where grasslands prevail in the plains and
deserts in the western cordillera.
Forests, grass-lands, deserts, represent the three chief types of
vegetation on the surface of the earth. Each is a response to certain
well-defined conditions of climate. Forests demand an abundance of
moisture throughout the entire season of growth. Where this season
lasts only three months the forest is very different from where it lasts
twelve. But no forest can be vigorous if the ground habitually becomes
dry for a considerable period during which the weather is warm enough
for growth. Desert vegetation, on the other hand, which consists
primarily of bushes with small, drought-resistant leaves, needs only a
few irregular and infrequent showers in order to endure long periods
of heat and drought. Discontinuity of moisture is the cause of deserts,
just as continuity is the necessary condition of forest growth. Grasses
prevail where the climatic conditions are intermediate between those of
the forest and the desert. Their primary requisite is a short period of
fairly abundant moisture with warmth enough to ripen their seeds. Unlike
the trees of the forests, they thrive even though the wet period be only
a fraction of the entire time that is warm enough for growth. Unlike
the bushes of the desert, they rarely thrive unless the ground is
well soaked for at least a few weeks. Most people think of forests as
offering far more variety than either deserts or grass-lands. To them
grass is just grass, while trees seem to possess individuality. In
reality, however, the short turfy grass of the far north differs from
the four-foot fronds of the bunchy saccaton grass of Arizona, and from
the far taller tufts of the plumed pampas grass, much more than the pine
tree differs from the palm. Deserts vary even more than either forests
or grass-lands. The traveler in the Arizona desert, for example, has
been jogging across a gravelly plain studded at intervals of a few yards
with little bushes a foot high. The scenery is so monotonous and the
noon sunshine so warm that he almost falls asleep. When he wakes from
his daydream, so weird are his surroundings that he thinks he must be in
one of the places to which Sindbad was carried by the roc. The trail has
entered an open forest of joshuas, as the big tree yuccas are called in
Arizona. Their shaggy trunks and uncouth branches are rendered doubly
unkempt by swordlike, ashy-yellow dead leaves that double back on the
trunk but refuse to fall to the ground. At a height of from twelve to
twenty feet each arm of the many-branched candelabrum ends in a stiff
rosette of gray-green spiky leaves as tough as hemp. Equally bizarre and
much more imposing is a desert "stand" of giant suhuaros, great fluted
tree-cacti thirty feet or more high. In spite of their size the suhuaros
are desert types as truly as is sagebrush.
In America the most widespread type of forest is the evergreen
coniferous woodland of the north. Its pines, firs, spruces, hemlocks,
and cedars which are really junipers, cover most of Canada together with
northern New England and the region south of Lakes Huron and Superior.
At its northern limit the forest looks thoroughly forlorn. The gnarled
and stunted trees are thickly studded with half-dead branches bent down
by the weight of snow, so that the lower ones sweep the ground, while
the upper look tired and discouraged from their struggle with an
inclement climate. Farther south, however, the forest loses this
aspect of terrific struggle. In Maine, for example, it gives a pleasant
impression of comfortable prosperity. Wherever the trees have room to
grow, they are full and stocky, and even where they are crowded together
their slender upspringing trunks look alert and energetic. The signs
of death and decay, indeed, appear everywhere in fallen trunks, dead
branches, and decayed masses of wood, but moss and lichens, twinflowers
and bunchberries so quickly mantle the prostrate trees that they do not
seem like tokens of weakness. Then, too, in every open space thousands
of young trees bank their soft green masses so gracefully that one has
an ever-present sense of pleased surprise as he comes upon this younger
foliage out of the dim aisles among the bigger trees.
Except on their southern borders the great northern forests are not good
as a permanent home for man. The snow lies so late in the spring and the
summers are so short and cool that agriculture does not prosper. As a
home for the fox, marten, weasel, beaver, and many other fur-bearing
animals, however, the coniferous forests are almost ideal. That is why
the Hudson's Bay Company is one of the few great organizations which
have persisted and prospered from colonial times to the present. As long
ago as 1670 Charles II granted to Prince Rupert and seventeen noblemen
and gentlemen a charter so sweeping that, aside from their own powers
of assimilation, there was almost no limit to what the "Governor and
Company of Adventurers of England trading into Hudson's Bay" might
acquire. By 1749, nearly eighty years after the granting of the charter,
however, the Company had only four or five forts on the coast of Hudson
Bay, with about 120 regular employees. Nevertheless the poor Indians
were so ignorant of the value of their furs and the consequent profits
were so large that, after Canada had been ceded to Great Britain in
1763, a rival organization, the Northwest Fur Company of Montreal, was
established. Then there began an era that was truly terrible for the
Indians of the northern forest. In their eagerness to get the valuable
furs the companies offered the Indians strong liquors in an abundance
that ruined the poor red man, body and soul. Moreover the fur-bearing
animals were killed not only in winter but during the breeding season.
Many mother animals were shot and their little ones were left to die.
Hence in a short time the wild creatures of the great northern forest
were so scarce that the Indians well-nigh starved.
In spite of this slaughter of fur-bearing animals, the same Company
still draws fat dividends from the northern forest and its furry
inhabitants. If the forest had been more habitable, it would long ago
have been occupied by settlers, as have its warmer, southern portions,
and the Company would have ceased to exist. Aside from the regions too
cold or too dry to support any vegetation whatever, few parts of the
world are more deadening to civilization than the forests of the far
north. Near the northern limit of the great evergreen forest of North
America wild animals are so rare that a family of hunting Indians can
scarcely find a living in a thousand square miles. Today the voracious
maw of the daily newspaper is eating the spruce and hemlock by means of
relentless saws and rattling pulp-mills. In the wake of the lumbermen
settlers are tardily spreading northward from the more favored tracts
in northern New England and southern Canada. Nevertheless most of the
evergreen forests of the north must always remain the home of wild
animals and trappers, a backward region in which it is easy for a great
fur company to maintain a practical monopoly.
Outliers of the pine forest extend far down into the United States. The
easternmost lies in part along the Appalachians and in part along the
coastal plain from southern New Jersey to Texas. The coastal forest
is unlike the other coniferous forests in two respects, for its
distribution and growth are not limited by long winters but by sandy
soil which quickly becomes dry. This drier southern pine forest lacks
the beauty of its northern companion. Its trees are often tall and
stately, but they are usually much scattered and are surrounded by
stretches of scanty grass. There is no trace of the mossy carpet and
dense copses of undergrowth that add so much to the picturesqueness of
the forests farther north. The unkempt half-breed or Indian hunter
is replaced by the prosaic gatherer of turpentine. As the man of the
southern forests shuffles along in blue or khaki overalls and carries
his buckets from tree to tree, he seems a dull figure contrasted with
the active northern hunter who glides swiftly and silently from trap to
trap on his rawhide snowshoes. Yet though the southern pine forest may
be less picturesque than the northern, it is more useful to man. In
spite of its sandy soil, much of this forest land is being reclaimed,
and all will some day probably be covered by farms.
Two other outliers of the northern evergreen forest extend southward
along the cool heights of the Rocky Mountains and of the Pacific coast
ranges of the United States. In the Olympic and Sierra Nevada ranges
the most western outlier of this northern band of vegetation probably
contains the most inspiring forests of the world. There grow the
vigorous Oregon pines, firs, and spruces, and the still more famous Big
Trees or sequoias. High on the sides of the Sierra above the yuccas, the
live oaks, and the deciduous forest of the lower slopes, one meets these
Big Trees. To come upon them suddenly after a long, rough tramp over
the sunny lower slopes is the experience of a lifetime. Upward the great
trees rise sheer one hundred feet without a branch. The huge fluted
trunks encased in soft, red bark six inches or a foot thick are
more impressive than the columns of the grandest cathedral. It seems
irreverent to speak above a whisper. Each tree is a new wonder. One has
to walk around it and study it to appreciate its enormous size. Where a
tree chances to stand isolated so that one can see its full majesty, the
sense of awe is tempered by the feeling that in spite of their size the
trees have a beauty all their own. Lifted to such heights, the branches
appear to be covered with masses of peculiarly soft and rounded foliage
like the piled-up banks of a white cumulus cloud before a thunderstorm.
At the base of such a tree the eye is caught by the sharp, triangular
outline of one of its young progeny. The lower branches sweep the
ground. The foliage is harsh and rough. In almost no other species of
trees is there such a change from comparatively ungraceful youth to a
superbly beautiful old age.
The second great type of American forest is deciduous. The trees have
broad leaves quite unlike the slender needles or overlapping scales of
the northern evergreens. Each winter such forests shed their leaves.
Among the mountains where the frosts come suddenly, the blaze of glory
and brilliance of color which herald the shedding of the leaves are
surpassed in no other part of the world. Even the colors of the Painted
Desert in northern Arizona and the wonderful flowers of the California
plains are less pleasing. In the Painted Desert the patches of red,
yellow, gray-blue, white, pale green, and black have a garish, almost
repellent appearance. In California the flame-colored acres of poppies
in some places, of white or yellow daisylike flowers in others, or of
purple blossoms elsewhere have a softer expression than the bare soil
of the desert. Yet they lack the delicate blending and harmony of colors
which is the greatest charm of the autumn foliage in the deciduous
forests. Even where the forests consist of such trees as birches,
beeches, aspens, or sycamores, whose leaves merely turn yellow in the
fall, the contrast between this color and the green tint of summer or
the bare branches of winter adds a spice of variety which is lacking in
other and more monotonous forests.
From still other points of view the deciduous forest has an almost
unequaled degree of variety. In one place it consists of graceful little
birches whose white trunks shimmering in the twilight form just the
background for ghosts. Contrast them with the oak forest half a mile
away. There the sense of gracefulness gives place to a feeling of
strength. The lines are no longer vertical but horizontal. The knotted
elbows of the branches recall the keels of sturdy merchantmen of bygone
days. The acorns under foot suggest food for the herds of half-wild pigs
which roam among the trees in many a southern county. Of quite another
type are the stately forests of the Appalachians where splendid magnolia
and tulip trees spread their broad limbs aloft at heights of one hundred
feet or more.
Deciduous forests grow in the well-balanced regions where summer and
winter approach equality, where neither is unduly long, and where
neither is subject to prolonged drought. They extend southward from
central New England, the Great Lakes, and Minnesota, to Mississippi,
Arkansas, and eastern Texas. They predominate even in parts of such
prairie States as Michigan, Indiana, southern Illinois, and southeastern
Missouri. No part of the continent is more populous or more progressive
than the regions once covered by deciduous forests. In the United States
nearly sixty per cent of the inhabitants live in areas reclaimed from
such forests. Yet the area of the forests is less than a quarter of the
three million square miles that make up the United States.
In their relation to human life the forests of America differ far more
than do either grass-lands or deserts. In the far north, as we have
seen, the pine forests furnish one of the least favorable environments.
In middle latitudes the deciduous forests go to the opposite extreme
and furnish the most highly favored of the homes of man. Still farther
southward the increasing luxuriance of the forests, especially along
the Atlantic coast, renders them less and less favorable to mankind. In
southern Mexico and Yucatan the stately equatorial rain forest, the most
exuberant of all types of vegetation and the most unconquerable by man,
makes its appearance. It forms a discontinuous belt along the wet east
coast and on the lower slopes of the mountains from southern Yucatan to
Venezuela. Then it is interrupted by the grasslands of the Orinoco, but
revives again in still greater magnificence in the Guianas. Thence
it stretches not only along the coast but far into the little known
interior of the Great Amazon basin, while southward it borders all the
coast as far as southern Brazil. In the Amazon basin it reaches its
highest development and becomes the crowning glory of the vegetable
world, the most baffling obstacle to human progress.
Except in its evil effects on man, the equatorial rain forest is the
antithesis of the forests of the extreme north. The equatorial trees are
hardwood giants, broad leaved, bright flowered, and often fruit-bearing.
The northern trees are softwood dwarfs, needle-leaved, flowerless, and
cone-bearing. The equatorial trees are often branchless for one hundred
feet, but spread at the top into a broad overarching canopy which shuts
out the sun perpetually. The northern trees form sharp little pyramids
with low, widely spreading branches at the base and only short twigs at
the top. In the equatorial forests there is almost no underbrush. The
animals, such as monkeys, snakes, parrots, and brilliant insects, live
chiefly in the lofty treetops. In the northern forests there is almost
nothing except underbrush, and the foxes, rabbits, weasels, ptarmigans,
and mosquitoes live close to the ground in the shelter of the branches.
Both forests are alike, however, in being practically uninhabited by
man. Each is peopled only by primitive nomadic hunters who stand at the
very bottom in the scale of civilization.
Aside from the rain forest there are two other types in tropical
countries--jungle and scrub. The distinction between rain forest,
jungle, and scrub is due to the amount and the season of rainfall. An
understanding of this distinction not only explains many things in
the present condition of Latin America but also in the history of
pre-Columbian Central America. Forests, as we have seen, require that
the ground be moist throughout practically the whole of the season that
is warm enough for growth. Since the warm season lasts throughout the
year within the tropics, dense forests composed of uniformly large trees
corresponding to our oaks, maples, and beeches will not thrive unless
the ground is wet most of the time. Of course there may be no rain for a
few weeks, but there must be no long and regularly recurrent periods of
drought. Smaller trees and such species as the cocoanut palm are much
less exacting and will flourish even if there is a dry period of several
months. Still smaller, bushy species will thrive even when the rainfall
lasts only two or three months. Hence where the rainy season lasts most
of the year, rain forest prevails; where the rainy and dry seasons do
not differ greatly in length, tropical jungle is the dominant growth;
and where the rainy season is short and the dry season long, the jungle
degenerates into scrub or bush.
The relation of scrub, jungle, and rain forest is well illustrated in
Yucatan, where the ancient Mayas reared their stately temples. On the
northern coast the annual rainfall is only ten or fifteen inches and is
concentrated largely in our summer months. There the country is covered
with scrubby bushes six to ten feet high. These are beautifully green
during the rainy season from June to October, but later in the year
lose almost all their leaves. The landscape would be much like that of
a thick, bushy pasture in the United States at the same season, were
it not that in the late winter and early spring some of the bushes bear
brilliant red, yellow, or white flowers. As one goes inland from the
north coast of Yucatan the rainfall increases. The bushes become taller
and denser, trees twenty feet high become numerous, and many rise thirty
or forty feet or even higher. This is the jungle. Its smaller portions
suggest a second growth of timber in the deciduous forests of the United
States fifteen or twenty years after the cutting of the original forest,
but here there is much more evidence of rapid growth. A few species of
bushes and trees may remain green throughout the year, but during the
dry season most of the jungle plants lose their leaves, at least in
part.
With every mile that one advances into the more rainy interior, the
jungle becomes greener and fresher, the density of the lower growths
increases, and the proportion of large trees becomes greater until
finally jungle gives place to genuine forest. There many of the trees
remain green throughout the year. They rise to heights of fifty or sixty
feet even on the borders of their province, and at the top form a canopy
so thick that the ground is shady most of the time. Even in the drier
part of the year when some of the leaves have fallen, the rays of the
sun scarcely reach the ground until nine or ten o'clock in the morning.
Even at high noon the sunlight straggles through only in small patches.
Long, sinuous lianas, often queerly braided, hang down from the trees;
epiphytes and various parasitic growths add their strange green and red
to the complex variety of vegetation. Young palms grow up almost in
a day and block a trail which was hewn out with much labor only a few
months before. Wherever the death of old trees forms an opening, a
thousand seedlings begin a fierce race to reach the light. Everywhere
the dominant note is intensely vigorous life, rapid growth, and quick
decay.
In their effect on man, the three forms of tropical forest are very
different. In the genuine rain forest agriculture is almost impossible.
Not only does the poor native find himself baffled in the face of
Nature, but the white man is equally at a loss. Many things combine to
produce this result. Chief among them are malaria and other tropical
diseases. When a few miles of railroad were being built through a
strip of tropical forest along the coast of eastern Guatemala, it was
impossible to keep the laborers more than twenty days at a time; indeed,
unless they were sent away at the end of three weeks, they were almost
sure to be stricken with virulent malarial fevers from which many died.
An equally potent enemy of agriculture is the vegetation itself. Imagine
the difficulty of cultivating a garden in a place where the weeds grow
all the time and where many of them reach a height of ten or twenty
feet in a single year. Perhaps there are people in the world who might
cultivate such a region and raise marvelous crops, but they are not the
indolent people of tropical America; and it is in fact doubtful whether
any kind of people could live permanently in the tropical forest and
retain energy enough to carry on cultivation. Nowhere in the world is
there such steady, damp heat as in these shadowy, windless depths
far below the lofty tops of the rain forest. Nowhere is there greater
disinclination to work than among the people who dwell in this region.
Consequently in the vast rain forests of the Amazon basin and in
similar small forests as far north as Central America, there are today
practically no inhabitants except a mere handful of the poorest and most
degraded people in the world. Yet in ancient times the northern border
of the rain forest was the seat of America's most advanced civilization.
The explanation of this contradiction will appear later. *
* See Chapter 5, Aztecs.
Tropical jungle borders the rain forest all the way from southern Mexico
to southern Brazil. It treats man far better than does the rain forest.
In marked contrast to its more stately neighbor, it contains abundant
game. Wild fruits ripen at almost all seasons. A few banana plants and
palm trees will well-nigh support a family. If corn is planted in a
clearing, the return is large in proportion to the labor. So long as
the population is not too dense, life is so easy that there is little to
stimulate progress. Hence, although the people of the jungle are
fairly numerous, they have never played much part in history. Far more
important is the role of those living in the tropical lands where scrub
is the prevailing growth. In our day, for example, few tropical lowlands
are more progressive than the narrow coastal strip of northern Yucatan.
There on the border between jungle and scrub the vegetation does not
thrive sufficiently to make life easy for the chocolate-colored natives.
Effort is required if they would make a living, yet the effort is not
so great as to be beyond the capacity of the indolent people of the
tropics.
Leaving the forests, let us step out into the broad, breezy grass-lands.
One would scarcely expect that a journey poleward out of the forest of
northern Canada would lead to an improvement in the conditions of human
life, yet such is the case. Where the growing season becomes so short
that even the hardiest trees disappear, grassy tundras replace the
forest. By furnishing food for such animals as the musk-ox, they are a
great help to the handful of scattered Indians who dwell on the northern
edge of the forest. In summer, when the animals grow fat on the short
nutritious grass, the Indians follow them out into the open country and
hunt them vigorously for food and skins to sustain life through the long
dreary winter. In many cases the hunters would advance much farther into
the grass-lands were it not that the abundant musk-oxen tempt the Eskimo
of the seacoast also to leave their homes and both sides fear bloody
encounters.
With the growth of civilization the advantage of the northern
grass-lands over the northern forests becomes still more apparent. The
domestic reindeer is beginning to replace the wild musk-ox. The
reindeer people, like the Indian and Eskimo hunters, must be nomadic.
Nevertheless their mode of life permits them to live in much greater
numbers and on a much higher plane of civilization than the hunters.
Since they hunt the furbearing animals in the neighboring forests during
the winter, they diminish the food supply of the hunters who dwell
permanently in the forest, and thus make their life still more
difficult. The northern forests bid fair to decline in population rather
than increase. In this New World of ours, strange as it may seem, the
almost uninhabited forest regions of the far north and of the equator
are probably more than twice as large as the desert areas with equally
sparse population.
South of the tundras the grass-lands have a still greater advantage over
the forests. In the forest region of the Laurentian highland abundant
snow lasts far into the spring and keeps the ground so wet and cold that
no crops can be raised. Moreover, because of the still greater abundance
of snow in former times, the largest of ice sheets, as we have seen,
accumulated there during the Glacial Period and scraped away most of
the soil. The grassy plains, on the contrary, are favored not only by
a deep, rich soil, much of which was laid down by the ice, but by the
relative absence of snow in winter and the consequent rapidity with
which the ground becomes warm in the spring. Hence the Canadian plains
from the United States boundary northward to latitude 57 degrees contain
a prosperous agricultural population of over a million people, while
the far larger forested areas in the same latitude support only a few
thousand.
The question is often asked why, in a state of nature, trees are so
scarce on the prairies--in Iowa, for instance--although they thrive
when planted. In answer we are often told that up to the middle of the
nineteenth century such vast herds of buffaloes roamed the prairies that
seedling trees could never get a chance to grow. It is also said that
prairie fires sweeping across the plains destroyed the little trees
whenever they sprouted. Doubtless the buffaloes and the fires helped
to prevent forest growth, but another factor appears to be still more
important. All the States between the Mississippi River and the Rocky
Mountains receive much more rain in summer than in winter. But as the
soil is comparatively dry in the spring when the trees begin their
growth, they are handicapped. They could grow if nothing else interfered
with them, just as peas will grow in a garden if the weeds are kept out.
If peas, however, are left uncared for, the weeds gain the upper hand
and there are no peas the second year. If the weeds are left to contend
with grass, the grass in the end prevails. In the eastern forest region,
if the grass be left to itself, small trees soon spring up in its midst.
In half a century a field of grass goes back to forest because trees
are especially favored by the climate. In the same way in the prairies,
grass is especially favored, for it is not weakened by the spring
drought, and it grows abundantly until it forms the wonderful stretches
of waving green where the buffalo once grew fat. Moreover the fine
glacial soil of the prairies is so clayey and compact that the roots of
trees cannot easily penetrate it. Since grasses send their roots only
into the more friable upper layers of soil, they possess another great
advantage over the trees.
Far to the south of the prairies lie the grass-lands of tropical
America, of which the Banos of the Orinoco furnish a good example.
Almost everywhere their plumed grasses have been left to grow
undisturbed by the plough, and even grazing animals are scarce. These
extremely flat plains are flooded for months in the rainy season from
May to October and are parched in the dry season that follows. As
trees cannot endure such extremes, grasses are the prevailing growth.
Elsewhere the nature of the soil causes many other grassy tracts to
be scattered among the tropical jungle and forest. Trees are at a
disadvantage both in porous, sandy soils, where the water drains away
too rapidly, and in clayey soil, where it is held so long that the
ground is saturated for weeks or months at a time. South of the tropical
portion of South America the vast pampas of Argentina closely resemble
the North American prairies and the drier plains to the west of
them. Grain in the east and cattle in the west are fast causing the
disappearance of those great tussocks of tufted grasses eight or nine
feet high which hold among grasses a position analogous to that of the
Big Trees of California among trees of lower growth.
It is often said that America has no real deserts. This is true in the
sense that there are no regions such as are found in Asia and Africa
where one can travel a hundred miles at a stretch and scarcely see a
sign of vegetation-nothing but barren gravel, graceful wavy sand dunes,
hard wind-swept clay, or still harder rock salt broken into rough blocks
with upturned edges. In the broader sense of the term, however, America
has an abundance of deserts--regions which bear a thin cover of bushy
vegetation but are too dry for agriculture without irrigation. On the
north such deserts begin in southern Canada where a dry region abounding
in small salt lakes lies at the eastern base of the Rocky Mountains.
In the United States the deserts lie almost wholly between the Sierra
Nevada and the Rocky Mountain ranges, which keep out any moisture that
might come from either the west or the east. Beginning on the north with
the sagebrush plateau of southern Washington, the desert expands to a
width of seven hundred miles in the gray, sage-covered basins of Nevada
and Utah. In southern California and Arizona the sage-brush gives place
to smaller forms like the saltbush, and the desert assumes a sterner
aspect. Next comes the cactus desert extending from Arizona far south
into Mexico. One of the notable features of the desert is the extreme
heat of certain portions. Close to the Nevada border in southern
California, Death Valley, 250 feet below sea-level, is the hottest
place in America. There alone among the American regions familiar to the
writer does one have that feeling of intense, overpowering aridity which
prevails so often in the deserts of Arabia and Central Asia. Some
years ago a Weather Bureau thermometer was installed in Death Valley at
Furnace Creek, where the only flowing water in more than a hundred miles
supports a depressing little ranch. There one or two white men, helped
by a few Indians, raise alfalfa, which they sell at exorbitant prices to
deluded prospectors searching for riches which they never find. Though
the terrible heat ruins the health of the white men in a year or two,
so that they have to move away, they have succeeded in keeping
a thermometer record for some years. No other properly exposed,
out-of-door thermometer in the United States, or perhaps in the world,
is so familiar with a temperature of 100 degrees F. or more. During the
period of not quite fifteen hundred days from the spring of 1911 to May,
1915, a maximum temperature of 100 degrees F. or more was reached on
five hundred and forty-eight days, or more than one-third of the time.
On July 10, 1913, the mercury rose to 134 degrees F. and touched the top
of the tube. How much higher it might have gone no one can tell. That
day marks the limit of temperature yet reached in this country according
to official records. In the summer of 1914 there was one night when the
thermometer dropped only to 114 degrees F., having been 128 degrees
F. at noon. The branches of a peppertree whose roots had been freshly
watered wilted as a flower wilts when broken from the stalk.
East and south of Death Valley lies the most interesting section of the
American desert, the so-called succulent desert of southern Arizona and
northern Mexico. There in greatest profusion grow the cacti, perhaps the
latest and most highly specialized of all the great families of plants.
There occur such strange scenes as the "forests" of suhuaros, whose
giant columns have already been described. Their beautiful crowns of
large white flowers produce a fruit which is one of the mainstays of the
Papagos and other Indians of the regions. In this same region the yucca
is highly developed, and its tall stalks of white or greenish flowers
make the desert appear like a flower garden. In fact this whole
desert, thanks to light rains in summer as well as winter, appears
extraordinarily green and prosperous. Its fair appearance has deceived
many a poor settler who has vainly tried to cultivate it.
Farther south the deserts of America are largely confined to plateaus
like those of Mexico and Peru or to basins sheltered on all sides from
rain-bearing winds. In such basins the suddenness of the transition
from one type of vegetation to another is astonishing. In Guatemala,
for instance, the coast is bordered by thick jungle which quickly gives
place to magnificent rain forest a few miles inland. This continues
two or three score miles from the coast until a point is reached where
mountains begin to obstruct the rain-bearing trade-winds. At once the
rain forest gives place to jungle; in a few miles jungle in its turn
is replaced by scrub; and shortly the scrub degenerates to mere desert
bush. Then in another fifty miles one rises to the main plateau passing
once more through scrub. This time the scrub gives place to grass-lands
diversified by deciduous trees and pines which give the country a
distinctly temperate aspect. On such plateaus the chief civilization of
the tropical Latin-American countries now centers. In the past, however,
the plateaus were far surpassed by the Maya lowlands of Yucatan and
Guatemala.
We are wont to think of deserts as places where the plants are of few
kinds and not much crowded. As a matter of fact, an ordinary desert
supports a much greater variety of plants than does either a forest or
a prairie. The reason is simple. Every desert contains wet spots near
springs or in swamps. Such places abound with all sorts of water-loving
plants. The deserts also contain a few valleys where the larger streams
keep the ground moist at all seasons. In such places the variety of
trees is as great as in many forests. Moreover almost all deserts have
short periods of abundant moisture.
At such times the seeds of all sorts of little annual plants, including
grasses, daisies, lupines, and a host of others, sprout quickly, and
give rise to a carpet of vegetation as varied and beautiful as that of
the prairie. Thus the desert has not only its own peculiar bushes and
succulents but many of the products of vegetation in swamps, grasslands,
and forests. Though much of the ground is bare in the desert, the plants
are actually crowded together as closely as possible. The showers of
such regions are usually so brief that they merely wet the surface. At
a depth of a foot or more the soil of many deserts never becomes moist
from year's end to year's end. It is useless for plants to send their
roots deep down under such circumstances, for they might not reach water
for a hundred feet. Their only recourse is to spread horizontally. The
farther they spread, the more water they can absorb after the scanty
showers. Hence the plants of the desert throttle one another by
extending their roots horizontally, just as those of the forest kill one
another by springing rapidly upward and shutting out the light.
Vegetation, whether in forests, grasslands, or deserts, is the primary
source of human sustenance. Without it man would perish miserably; and
where it is deficient, he cannot rise to great heights in the scale of
civilization. Yet strangely enough the scantiness of the vegetation of
the deserts was a great help in the ascent of man. Only in dry regions
could primitive man compete with nature in fostering the right kind
of vegetation. In such regions arose the nations which first practised
agriculture. There man became comparatively civilized while his
contemporaries were still nomadic hunters in the grasslands and the
forests.