legend of African deserts, no death-news of the many adventurous
travelers who have gone forth to seek the source of the Niger,
frighten him back. On the west coast of Africa, in the Canary
Isles, is, indeed, no longer found the gigantic dog, from which,
as Pliny told, the islands derived their name, but Flora gives for
booty richest treasures which she, by aid of the tropical sun, has
succeeded in extracting from the soil, moistened by the vapors of
the ocean. Round sycamores twine mighty cissus stems; capers and
bauhinias interlace in the thickets of balsamic shrubs. The slender
date-palm soars aloft, and the baobab grows up into gigantic masses
of wood. The wondrous cactus-like forms of the leafless spurges,
distinguished by their poisonous or pleasant-flavored, sweet milk,
as the case may be, betray a peculiar formative power in Nature;
and the dragon-tree in the garden of Orotava,[3] in Teneriffe, a
gigantic arborescent lily-plant, recounts to the musing listener the
traditions of thousands of years.
Six zones of vegetation have we thus passed through, in which the
continually increasing temperature of the climate called forth ever
a different, ever a more luxuriant vegetation, and we conclude
our wanderings, after a short rest under the five-thousand-yeared
Dracænas, by climbing the Pic of Teyde. Man has taken possession
of the soil of the plain at its foot and dislodged the original
vegetation. Through vineyards and maize-fields we ascend, till
the shades of the evergreen bay-laurel surround us. Trees of the
lace-bark tribe and similar plants succeed; we wander for a time
through a _zone of evergreen forest trees_. At a height of 4,000
feet we lose the plants which had so far accompanied us. A very
small number of peculiar plants mark a quickly traversed _zone of
deciduous trees_, and we come among the resinous trunks of the Canary
pine. A _zone of conifers_ shield us from the sun’s rays up to a
height of 6,000 feet, then the vegetation suddenly becomes low--from
humble bushes it passes into a flora which bears all the characters
of the Alpine plants, till finally the naked rock sets a limit to all
organic life, and no snow and ice bedeck the summit of the mountain,
only because its height of 12,236 feet does not, in a position so
near the tropics, extend up to the region of eternal snow. Counting
by the limits of vegetation, we have resurveyed in a few hours’ climb
the wide way from Spitzbergen to the Canaries, an extent of more than
fifty degrees of latitude.
The plant is dependent on the condition of the soil, in the widest
sense of the word, on the store of nutriment it contains, and on all
that influences the chemical process of formation, consequently,
above all, upon a determinate temperature. The universal,
indispensable nutrient substance of plants, and, at the same time,
the matter by means of which all the rest are conveyed into it,
is water. Without water there is no vegetation. The orchidaceous
plants of the tropical forest let their peculiarly constructed roots
hang down from the branch to which they cling in the warm, moist
atmosphere, and absorb water in the form of vapor. Our water-lilies
and the proper bog-plants will only flourish when surrounded by
liquid water, or, at least, with their roots dipping in it. The case
is quite different with the great majority of plants; they have to
extract their nutriment from the earth, which contains the moisture
to be absorbed into them in a peculiar condition. If to these three
classes of air, water, and earth-plants we add one more, namely,
the true parasites, which, like our dodder, draw their organized
nutriment from other plants, we have obtained the principal divisions
of stations.
Every soil which bears plants contains also in its composition all
the substances required by all plants, only the proportions differ,
and the predominance of silex, lime, or common salt must consequently
favor especially the growth of grasses, pulses, or shore-plants,
although these are by no means exclusively confined to the proper
sandy or calcareous soils, or to the seaside. In addition to the
chemical conditions, there is yet another which modifies the former
and, where it brings about the same actions, contributes to chain
particular plants so much the more firmly, exclusively to particular
soils, or contrariwise also contributes to conceal or obliterate
the connection between plants and the chemical nature of the soil.
This consists in the mechanical condition and physical peculiarities
of the soil. There are plants which will only settle on unbroken
_rocks_, which when the other conditions coincide, spring from these
rocks over on to our _walls_, like the Wall Rue Spleenwort,[4] a
little fern, the name of which denotes its station. Others occur only
where weathering has broken up the solid rock into small fragments,
_drift_ plants, which, clinging to mankind, select _rubbish heaps_,
which most resemble their natural station; our great nettle and
henbane may serve as examples. Lastly, other plants grow only where
the rocks have been reduced to fine powder, in _sand_ or in the
fine-grained _clay_ produced by chemical decomposition. The so-called
German Sarsaparilla, the sea-reed, is an example of the first
condition, but there is no definite condition corresponding to it in
the vicinity of human habitations. Clay, on the other hand, stands
beside the black substance humus, resulting from the decomposition of
organic matter. Both rich in soluble salts, important to vegetation,
both distinguished in regard to their property of absorbing from
the atmosphere, and thus conveying to the roots of plants gases
and aqueous vapor, they cause, singly or in combination, the most
luxuriant vegetation. We thus obtain three stages in reference to
the qualities of the soil-pure earths, wholly devoid of vegetation;
mixed earths, without clay or humus, with an arid but characteristic
vegetation; and lastly, soil rich in clay and humus, with the
greatest abundance and variety of plants.
Australia has, in common with Europe, a very common plant, the daisy
(_Bellis perennis_). The same little flower is found in northern
Asia, in some regions in Africa and South America, and where it
occurs it climbs the mountains from the level of the sea up to
the snow-limit. The little enchanter’s nightshade, the delicate
Linnæa, the bittersweet, the bird’s knot-grass, the blue gentian,
the dwarf birch, and the herbaceous willow, and several others, are
indigenous both in Europe and North America. The common self-heal,
the duckweed, and our reed grow in New Holland. The bog-moss covers
the moors of Peru and New Granada, as well as those of the Hartz and
of Dovrefjeld in Norway. The brownish Parmelia, which clothes all our
walls in Germany, palings, and old trees, is no less present on the
only ninety-year-old Yorullo in Mexico. The bluish bristle-grass,
which is one of the commonest garden and field weeds on sandy soils
with us, grows also in the interior of Brazil on suitable soil. A
characteristic plant of the seashores of Northern Europe and the
vicinity of salt-springs, _Ruppia martima_, grows equally on the
northern coast of Germany, in Brazil, and the East Indies. But it
is needless to accumulate examples, for these so hasten to present
themselves that the view finds some support in observation which
assumes that every plant must exist in every part of the globe where
the known conditions of its vegetation are present.
The little daisy (_Bellis perennis_) exhibits a certain wilfulness.
It is wanting all through North America; and that which we tread down
as an insignificant weed in our European meadows is there reared
with the most tender care in the botanical gardens. If we pass in
review the vegetation of different countries, we see that causes
appearing similar in our present knowledge of them bring forth indeed
_similar_, but by no means the same, forms of plants. To the plants
of a particular northern latitude correspond in the analogous height
of the Alps, situated southward, other species of the same genera,
or other genera of the same family; or the plants of America are
represented in the same latitudes in the Old World by plants which
are different, but closely allied, in their development. Nay, even
plants which belong to totally different families assume, at least
in their outward appearance, similar shapes. Thus the cactus plants
of the New World correspond to the leafless, fleshy spurges of the
torrid Africa.
If, again, we anticipate that a greater variety of conditions of
vegetation is the cause why the variety of vegetation, the number
of species of plants, continually augments from the pole toward the
equator, and that on the same account the number of sociably growing
plants, of species which clothe great tracts in countless individual
specimens, also increases in the same measure, we find that we are
still far from being enabled to give a scientific account of the
matter. It seems to us wholly the result of caprice that particular
plants are distributed widely over the globe, while others must
live cribbed in the narrowest spot, as, for instance, the Wulfenia,
occurring exclusively on the Carinthian Alps; that particular
families, like the _Compositæ_, flourish abroad over the whole earth,
while others, like the peppers and the palms, only occur between
very definite degrees of latitude on either side of the equator, the
_Proteaceæ_ only in the Southern Hemisphere, the cactus tribe only in
the western half of our earth. Just as inexplicable is the _mode of
distribution_ of the families of plants. While the palms diminish in
number from the equator into higher latitudes, the _Compositæ_ attain
their highest development in the zones of mean temperature, their
number of species diminishes from these in both directions, equally
toward the equator and toward the poles; while, finally, the grasses
increase constantly from the equator toward the poles.
This, to us inexplicable, mode of distribution of plants according
to species, genera, families, orders, and classes gives rise to
certain peculiar regions on the globe, which are characterized by
the predominance of certain forms of plants, or by the exclusive
occurrence of particular families. These portions of the earth’s
surface are called Geographical Regions of Plants, and to them have
been applied the names of men who have made themselves especially
famous by the investigation of these places.
I have already alluded to the regions of saxifrages and mosses, or
Wahlenberg’s region, which extends from the eternal snow of the
poles, or the summits of the mountains, down to the limit of the
growth of trees, and is distinguished by the absence of arborescent
plants, and even of the taller shrubs. Adjoining this comes the
great Linnæan region, including northern Europe and northern Asia
to the great chain of mountains which extends from the Pyrenees to
the Alps. Woods of conifers, or deciduous trees, luxuriant meadows,
and broad heaths, in Asia the peculiar salt steppes, especially
determine the characters of this region, which, at least in its
European portion, is now too widely taken possession of to exhibit
its natural physiognomy. The wide basin from the Alps to Atlas, the
deepest part filled by the Mediterranean Sea, forms a third region,
distinguished by the abundance of aromatic Labiate plants, fair, but
fleeting, lily plants, and the resinous rock-roses. The solitary
dwarf-palm and balsam-trees denote in this, De Candolle’s region, the
transition to the tropics. Parallel to the two last-named regions,
North America is divided into a northern region named in honor of
Michaux, distinguished by peculiar conifers, oaks and walnuts, by
innumerable asters and golden-rods from the Linnæan region, and
a southern, Pursh’s region, in which most strikingly appear the
trees with broad shining leaves and large splendid flowers, like
the tulip-tree, the magnolia, and others defining the character.
Between Kämpfer’s region, comprehending China and Japan, Wallich’s
in the highlands of India, and the Polynesian, or island region of
Reinwardt, renowned for its poison-tree and its giant-flower, lies
Roxburgh’s region, which extends through both the Indian peninsulas,
which conceals among the shadows of the monster fig-trees the
_Scitaminaceæ_, or aromatic lilies, like ginger, cardamums, and
turmeric, or in little woods of aromatic barks, like the cinnamon and
cassia, matures in thick, shapeless stems the starch of the sago.
We pass over Blume’s region in the mountains of Java, Chamisso’s
in the Archipelago of the South Sea, and Forster’s region in New
Zealand, and turn again to Africa, where the desert, Delile’s region,
ripens, in the oases, the date, and in the tender-leaved acacias
concocts the abundance of gum-arabic and senega, which commerce
brings to the service of our industry. To this, eastward, adjoins
Forskäl’s region, where the balsam-trees predominate; on the south,
Adanson’s, the characteristic plant of which perpetuates the name
of that enlightened botanist, the thousand-yeared giant stem of the
_Adansonia digitata_, the baobab, or monkey’s-bread. The little
known Africa gives only one more region, at its southern extremity,
Thunberg’s, bedecked with stapelias, mesembryanthemums, brilliant
heaths, and evil-scented becku-shrubs, but poor in woods. New Holland
and Van Diemen’s Land bear the name of their first and most profound
botanical investigator, Robert Brown; and Central and South America
distribute their vegetable riches into eight more regions, which are
dedicated to Jacquin, Bonpland, Humboldt, Ruiz and Pavon, Swartz,
Martius, St. Hilaire, and D’Urville; among these, Jacquin’s region is
remarkable for its strange cacti; Humboldt’s, on the heights of the
South American Andes, for its Quinoa forests; and that of Martius, in
the interior of Brazil, for its abundance of palms, for its quantity
of climbing plants or lianes and parasitic plants.
All over the globe has man, for the supply of necessary food,
selected almost solely summer plants, that is, such plants as
complete their whole vegetative processes, or, at all events, the
development of all the parts containing nutrient matter, within
the course of a few months. By this means he has rendered himself
independent in the half-tropical regions of the evil action of the
dry season, and in the higher latitudes of the destructive influence
of cold, and thus ensured the possibility of cultivating plants,
which there must be killed by the drought of summer, here by the
cold of winter. Setting aside the cultivation of fruits, which serve
rather pleasure than necessity, there remain but three arborescent
vegetables in the whole world which can be included among the true
food-plants, namely, the bread-fruit, the cocoanut, and the date,
which actually furnish the chief proportion of the food of great
bodies of men and over widely extended areas, and thence have become
objects of culture; the _Cycadaceæ_, and sago-palms, on account of
their starchy parenchyma, can at most perhaps be taken into our
reckoning only in a very limited circle in the East Indies. All the
rest of the food-plants are either such as possess a subterraneous,
usually tuberous stem, which sends up shoots above the soil,
persisting but a few months, on which develop flowers and fruit,
while during the remaining time sleeping, as it were, beneath the
protecting coverlet of earth, it sets the disfavor of the climate at
defiance, or such as die during or at the end of a short period of
vegetation, and ensure the future reproduction in the slumbering germ
of the seed. To the former belong, for instance, the potato, derived
from the Cordilleras of Chili, Peru, and Mexico; to the latter,
almost all our corn-plants.
One plant alone distinguishes itself among the cultivated plants
by a peculiar mode of vegetation, a plant which was perhaps the
earliest gift of Nature to man awakening to life, and thus the
object of the earliest culture; I mean the banana. And this plant
was not merely the first, but the most valuable gift of Nature; its
slightly aromatic, sweet and nutritive fruits are the sole, or at
least the chief, food of the major part of the inhabitants of the
hotter regions. A creeping subterraneous root-stock sends out on
high, from lateral buds, a shaft fifteen to twenty feet long, which
consists merely of the rolled-up, sheath-like leaf-stalks, bearing
the velvet-like glancing leaves, often ten feet long and two feet
broad; the midrib of the leaf alone is firm and thick, but the blade
of the leaf on either side so delicate that it is readily torn by the
wind, whence the leaf acquires a peculiar feathered aspect. Among
the leaves presses up the rich cluster of flowers, which within
three months after the shoot has arisen forms from 150 to 180 ripe
fruits, about the size and form of a cucumber. The fruits weigh
altogether about 70 or 80 pounds, and the same space which will bear
1,000 pounds of potatoes brings forth in a much shorter time 44,000
bananas; and if we take account of the nutritious matter which this
fruit contains, a surface which, sown with wheat, feeds one man,
planted with bananas, affords sustenance to five-and-twenty. Nothing
strikes the European landing in a tropical country so much as the
little spot of cultivated land round a hut, which shelters a very
numerous Indian family.
Not till long after did man learn to know and cultivate the gifts of
Ceres. It must, in fact, surprise us, at present, to see that but
a few species of a single family of plants furnish the principal
food of the greater proportion of mankind, namely, the so-called
corn-plants, or _Cerealia_, of the family of grasses. This family
includes nearly 4,000 species, and yet not twenty of them are
cultivated for the food of man. In their real nature these cultivated
grasses are all summer plants, but varieties have been obtained from
some of the most important of them, which, in the proper climate,
sown in autumn, germinate and pass the winter under the warm covering
of snow, so that they are in a condition to shoot out strongly in the
spring, while the soil is being prepared for the other summer plants.
Barley has the widest range of distribution of all the _Cerealia_,
and is cultivated from the extreme limits of culture in Lapland to
the heights immediately beneath the equator. But it has by no means
the same importance everywhere that it has in the northern region,
where, in a little narrow zone, it appears as the sole bread-corn.
In Lapland and northern Asia, rye soon appears beside it, but by
the inclemency of the climate confined to favorable years, and
therefore not properly to be regarded as the principal food. First in
Norway, Sweden, Finland, and Russia does the rye become the peculiar
bread-corn; and wheat takes its place beside it in the north of
Great Britain and Germany, as the rye before joined barley. In the
centre of Germany, in the south of Great Britain, in France, and in a
wide range toward the East, including the whole of the Caspian Sea,
wheat is the prevailing cultivated plant, which in the basin of the
Mediterranean and throughout North America is associated with maize.
Rice takes the place of the latter in Egypt and in northern India,
and holds undisputed rule in the peninsulas of India, in China,
Japan, and the East Indian islands, shares it in the west coast of
Africa with maize, which, on the other hand, is the exclusively
cultivated corn-plant of the greatest part of tropical America,
with only some unimportant exceptions. In southern America, Africa,
and Australia wheat again enters the field with the decreasing
temperature. The culture of _Tef_ and _Tocusso_ in Abyssinia, of
millet in Western Africa and Arabia, as well as of _Eleusine_ and
millet in the East Indies, are quite of subordinate importance.
Some other plants bear a far more important share in the nutrition
of mankind than the grasses last named. Even in the most northern
zone of the barley and rye, the buckwheat is an object of tolerably
extensive culture. With the already named banana, the yams, the
manioc, and the batatas contribute largely to the daily food of the
inhabitants of the tropics, of the Old as of the New World, added to
which the Andes presents itself a peculiar vegetable, the quinoa,
a plant which simultaneously produces edible tubers and abundance
of seeds, comparable to those of buckwheat. Lastly, we may not pass
over the _Bread-fruit_, in the proper sense of the word, which is
the principal food of the inhabitants of the large islands which
extend from the East Indies through the whole tropical ocean to the
west coast of America, the gift of a large and beautiful tree of the
family of the nettle, which from the use it is turned to is called
the bread-fruit tree. For the sake of variety, some also cultivate
with it the tarroo-root, the _Tacca_ tubers, or some ferns, the
farinaceous leaf-stalks of which afford a dainty meal. Last of all I
will mention the potato, which has spread over the whole earth with
such rapidity from the mountains of the New World that in many places
it threatens, not exactly to the advantage of mankind, to supplant
every other culture.
PHYSIOGNOMY OF PLANTS
--ALEXANDER VON HUMBOLDT
The carpet of flowers and of verdure spread over the naked crust of
our planet is unequally woven; it is thicker where the sun rises high
in the ever cloudless heavens and thinner toward the poles, in the
less happy climes where returning frosts often destroy the opening
buds of spring or the ripening fruits of autumn. Everywhere, however,
man finds some plants to minister to his support and enjoyment.
Lichens form the first covering of the naked rock, where afterward
lofty forest trees rear their airy summits. The successive growth of
mosses, grasses, herbaceous plants and shrubs or bushes, occupies
the intervening period of long but undetermined duration. The part
which lichens and mosses perform in the northern countries is
effected within the tropics by Portulacas Gomphrenas and other low
and succulent shore-plants. The history of the vegetable covering of
our planet, and its gradual propagation over the desert crust of the
earth, has its epochs as well as that of the migrations of the animal
world.
When leaving our oak forests, we traverse the Alps or Pyrenees, and
enter Italy or Spain, or when we direct our attention to some of the
African shores of the Mediterranean, we might easily be led to draw
the erroneous inference that hot countries are marked by the absence
of trees. But those who do so, forget that the south of Europe wore
a different aspect on the first arrival of Pelasgian or Carthaginian
colonies; they forget that an ancient civilization causes the
forests to recede more and more, and that the wants and restless
activity of large communities of men gradually despoil the face of
the earth of the refreshing shades which still rejoice the eye in
northern and middle Europe, and which even more than any historic
documents prove the recent date and youthful age of our civilization.
The deserts to the south of the Atlas, and the immense plains or
steppes of South America, must be regarded as only local phenomena.
The latter, the South American steppes, are clothed, in the rainy
season at least, with grass and with low-growing, almost herbaceous,
mimosas. The African deserts are, indeed, at all seasons, devoid of
vegetation; seas of sand, surrounded by forest shores clothed with
perpetual verdure. A few scattered fan-palms alone recall to the
wanderer’s recollection that these awful solitudes belong to the
domain of the same animated terrestrial creation which is elsewhere
so rich and so varied. The fantastic play of the mirage, occasioned
by the effects of radiant heat, sometimes causes these palm trees
to appear divided from the ground and hovering above its surface,
and sometimes shows their inverted image reflected in strata of
air undulating like the waves of the sea. On the west of the great
Peruvian chain of the Andes, on the coasts of the Pacific, I have
passed entire weeks in traversing similar deserts destitute of water.
When once a region has lost the covering of plants with which it was
invested, if the sands are loose and mobile and are destitute of
springs, and if the heated atmosphere, forming constantly ascending
currents, prevents precipitation taking place from clouds, thousands
of years may elapse ere organic life can pass from the verdant shores
to the interior of the sandy sea, and repossess itself of the domain
from which it had been banished.