Chapter LXII: 1204. What are vegetable oils and fats?

Vegetable oils and fats constitute, next to starch and sugar, the most important secretion of the vegetable creation. There are very few plants from which some amount of oil cannot be obtained; and those which are famed for yielding it owe their celebrity rather to the abundance that they yield, and the peculiar qualities of their oil, than to the secretion of oil being rare--for probably there is no plant without it.

Oil is most commonly found in seeds, as _rape-seed_, _linseed_, &c., but it is found also in leaves, as in the rose, sweet-briar, peppermint, &c., where its presence may be recognised by the distinguishing perfume; and it is also found in the wood of a few trees, such as the sassafras and the sandal-wood; the bark frequently yields an oily secretion.

[Verse: "Ointment and perfume rejoice the heart; so doth the sweetness of a man's friend by hearty counsel."--PROVERBS XXVII.]

The London and North Western Railway Company alone use about
50,000 gallons of oil yearly.

1205. _Why are fat and oil found most abundantly in the bodies of animals in cold climates_?

Because they contribute to keep the _bodies of animals warm_, not only by their non-conducting property _keeping in_ the heat of the animals, but by supplying _carbon_ abundantly to combine with _oxygen_ during respiration, and thereby developing _animal heat_.

1206. _Why are oil and fat-forming trees found most abundantly in hot climates?_

Because, in hot countries, the formation of large quantities of fat in animal bodies would oppress living creatures with heat; fats and oils are, therefore, produced in those countries chiefly by vegetables, and are used externally by the Asiatics and Africans as an _external_ unction for _cooling the skin_, and as _perfumes_ which give inspiriting properties to the air, rendered oppressive by excess of heat.

1207. _Why are succulent fruits most abundant in tropical climates?_

Because they are rendered necessary in those climates by the _excessive heat_, and are found to have a most beneficial effect in cooling, purifying the blood of the inhabitants of tropical countries; while the grandeur of their foliage, and the richness of their flowers, are in perfect keeping with the intensity of light and heat, and serve, by throwing dense shades over the earth, to cool its surface, and to offer to living creatures a pleasant retreat from the rays of the burning sun.

The following sketch of _Botanical Geography_ should be read
attentively after the reader has gone through the whole of the
Chapters of "Reasons." The technical terms employed in the course
of the article are nearly all explained at 1212, and should
be committed to memory at the commencement of the perusal.
_Mimosa_ means a sensitive plant; _concentric zones_, circular
lines spreading from a centre; _arborescent_, resembling trees;
_Gramineæ_, grass-like. The botanical names represent individual
plants.

[Verse: "Blessed is the man that walketh not in the counsel of the ungodly, nor standeth in the way of sinners, nor sitteth in the seat of the scornful:"]

1208. When treating of the geographical distribution of
vegetables, we have to mark the general arrangements indicated,
and the agencies that have evidently operated in promoting the
diffusion of floral tribes. Vegetation occurs over the whole
globe, therefore, under the most opposite conditions. Plants
flourish in the bosom of the ocean as well as on land, under the
extremes of cold and heat in polar and equatorial regions, on
the hardest rocks and the soft alluvium of the plains, amidst
the perpetual snow of lofty mountains, and in springs at the
temperature of boiling water, in situations never penetrated by
the solar rays, as the dark vaults of caverns, and the walls of
mines, as well as freely exposed to the influences of light and
air. But these diverse circumstances have different species and
genera. There is only one state which seems fatal to the existence
of vegetable life--the entire absence of humidity.

1209. By species we understand so many individuals as intimately
resemble each other in appearance and properties, and agree in all
their permanent characters, which are founded in the immutable
laws of creation. An established species may frequently exhibit
new varieties, depending upon local and accidental causes,
but these are imperfectly, or for a limited time, if at all,
perpetuated.

1210. A genus comprises one or more species similar to each other,
but essentially differing in formation, nature, and in many
adventitious qualities from other plants. A tribe, family, group,
or order, comprises several genera.

1211. The known number of species in the vegetable kingdom has
been gradually enlarged by the progress of maritime and inland
discovery; but owing to great districts of the globe not having
yet been explored by the botanist, the interior of Africa, and
Australia, with sections of America, Asia, and Oceanica, it is
impossible to state the exact amount. The successive augmentation
of the catalogue appears from the numbers below:

Species.
Theophrastus 500
Pliny 1,000
Greek, Roman, and Arabian botanists 1,400
Bauhin 6,000
Linnæus 8,800
Persoon 27,000
Humboldt and Brown 38,000
De Candolle 56,000
Lindley 86,000
Hinds 89,000

1212. Vegetable forms are divided into three great classes
which differ materially in their structure:--1. Cryptogamous
plants--those which have no flowers, properly so called, mosses,
lichens, fungi, and ferns: as distinguished from those which
are phænogamous, or flower-bearing, to which the two following
classes belong. 2. Endogenous plants, which have stems increasing
from within, also called Monocotyledons, from having only one
seed-lobe, as the numerous grasses, lilies, and the palm family.
3. Exogenous plants, which have stems growing by additions from
without, also called Dicoteledons, from the seed consisting of two
lobes, the most perfect, beautiful, and numerous class, embracing
the forest trees, and most flowering shrubs and herbs.

1213. The exogens furnish examples of gigantic size, and great
longevity. In South America on the banks of the Atabapo, Humboldt
measured a _Bombax caiba_ more than 120 feet high, and 15 in
diameter; and near Cumana, he found the _Zamang del Guayra_, a
species of mimosa, the pendant branches of the hemispherical head
having a circumference of upwards of 600 feet. The _Adansonia_, or
baobab of Senegal, though attaining no great height, rarely more
than fifty feet, has a trunk with a diameter sometimes amounting
to 34 feet; while the _Pinus Lambertiana_, growing singly on the
plains west of the Rocky Mountains, has been found 250 feet high,
60 feet in circumference at the base, 4-1/2 feet in girth at the
height of 190 feet, yielding cones 11 inches round, and 16 long.
The _Ficus Indicus_, or banian tree, sending out shoots from its
horizontal branches, which reaching the ground take root, and form
new stems till a single tree multiplies almost to a forest, has
been observed covering an area of 1700 square yards.

[Verse: "He shall be like a tree planted by the rivers of water, that bringeth forth his fruit in season: his leaf also shall not wither; and whatsoever he doeth shall prosper."--PSALM I.]

1214. From the number of concentric zones observed in a transverse
section of the stems De Caudolle advances proof of the following
ages:

Elm 335 years.
Cypress about 350 "
Cheirostemon " 400 "
Ivy 450 "
Larch 576 "
Orange 630 "
Olive 700 "
Oriental Plane " 720 " and upwards.
Cedar of Lebanon " 800 "
Oak 810, 1080, 1500 "
Lime 1076, 1147 "
Yew 1214, 1458, 2588, 2880 "
Taxodium 4000 to 6000 "
Baobab 5150 "

1215. Admitting, with Professor Henslow, that De Candolle
overrated the ages of these trees one-third, they are examples of
extraordinary longevity. Yew trees upwards of 700 years old remain
at Fountains Abbey, Yorkshire, as there is historic evidence of
their existence in the year 1133. But a yew in the churchyard of
Darley-in-the-Dale, Derbyshire, is considered by Mr. Bowman as
2000 years old.

1216. The cryptogamous plants afford the most numerous examples of
wide diffusion. A lichen indigenous in Cornwall, _sticta aurata_,
is also a native of the West India Islands, Brazil, St Helena, and
the Cape of Good Hope; while 38 lichens and 28 mosses are common
to Great Britain and Australia, though the general vegetation
of the two districts is remarkably discordant. Some species
of endogenous plants are also widely distributed, the _Phleum
alpinum_ of Switzerland occurring without the slightest difference
at the Strait of Magellan, and the quaking grasses of Europe in
the interior of Southern Africa. But only in very few instances
are the same species of exogenous plants met with in regions far
apart from each other; and generally speaking, in passing from
one country to another, we encounter a new flora; for if the same
genera occur, the species are not identical, while in districts
widely separated the genera are different.

1217. The cryptogamic plants, mosses, lichens, ferns, and fungi,
are to the whole mass of phænogamic vegetation in the following
proportions in different districts: Equatorial latitudes, 0 deg.
to 10 deg.; on the plains, 1-25th, on the mountains, 1-5th;
mean latitudes, 45 deg. to 52 deg. 1/2; high latitudes, 67 deg.
70 deg., proportion about equal. Thus the proportion of the
flowerless vegetation to the flowering increases from the equator
to the poles. But the family of ferns, _filices_, viewed singly,
forms an exception to this law, decreasing as we depart from
equinoctial countries, being 1-20th in equatorial and 1-70th in
mean latitudes, and not found at all in the high latitudes of the
new world.

[Verse: "To give unto them beauty for ashes, the oil of joy for mourning, the garment of praise for the spirit of heaviness; that they might be called Trees of righteousness, The planting of the Lord, that he might be glorified."--ISAIAH LXI.]

1218. In equinoctial and tropical countries, where a sufficient
supply of moisture combines with the influence of light and heat,
vegetation appears in all its magnitude and glory. Its lower
orders, mosses, fungi, and confervæ, are very rare. The ferns
are aborescent. Reeds ascend to the height of a hundred feet,
and rigid grasses rise to forty. The forests are composed of
majestic leafy evergreen trees bearing brilliant blossoms, their
colours finely contrasting, scarcely any two standing together
being of the same species. Enormous creepers climb their trunks;
parasitical orchidæ hang in festoons from branch to branch, and
augment the floral decoration with scarlet, purple, blue, rose,
and golden dyes. Of plants used by man for food, or as luxuries,
or for medicinal purposes, occurring in this region, rice,
bananas, dates, cocoa, cacao, bread-fruit, coffee, tea, sugar,
vanilla, Peruvian bark, pepper, cinnamon, cloves, and nutmegs, are
either characteristic of it as principally cultivated within its
limits, or entirely confined to them.

1219. Rice (_Oryza-sativa_), the chief food of, perhaps, a
third of the human race, is cultivated beyond the tropics, but
principally within them, only where there is a plentiful supply
of water. It has never been found wild; its native country is
unknown; but probably southern Asia.

1220. Bananas, or plantains (_Musa sapientum et paradisiaca_), are
cultivated in intertropical Asia, Africa, and America. The latter
species occur in Syria. The banana is not known in an uncultivated
state. Its produce is enormous, estimated to be on the same space
of ground to that of wheat, as 133 to 1, and to that of potatoes
as 44 to 1.

1221. Dates (_Phoenix dactylifera_), and cocoa (_Cocos nucifera_),
belonging to the family _Palmæ_. The palms, remarkable for
their elegant forms and importance to man, contribute more than
any other trees to impress upon the vegetation of tropical and
equinoctial countries its peculiar physiognomy. The date palm
is a native of northern Africa, and is so abundant between the
Barbary states and the Sahara, that the district has been named
Biledul erid, the land of dates. As the desert is approached, the
only objects that break the monotony of the landscape are the
date palm, and the tent of the Arab. It accompanies the margin
of the mighty desert in all its sinuosities from the shores of
the Atlantic to the confines of Persia, and is the only vegetable
affording subsistence to man that can grow in such an arid
situation. The annual produce of an individual is from 150 to
260lbs. weight of fruit. The cocoa palm furnishes annually about a
hundred cocoa-nuts. It is spread throughout the torrid zone; but
occurs most abundantly in the islands of the Indian archipelago.
The family of palms is supposed to contain a thousand species,
some of large size, forming extensive forests.

1222. Cacao (_Theobrama cacao_), from the seeds of which
chocolate is prepared, grows wild in central America, and is also
extensively cultivated in Mexico, Guatemala, and on the coast of
Cumana.

1223. Bread-fruit tree (_Artocarpus incisa_), a native of the
South Sea Islands, and Indian archipelago, grows also in Southern
Asia, and has been introduced into the tropical parts of America;
but the fruit is not equal to the banana as an article of human
food.

[Verse: "And they returned and prepared spices and ointments; and rested the Sabbath-day, according to the commandment."--LUKE XXIV.]

1224. Coffee (_Coffea Arabica_). The bush has probably for its
native region the Ethiopian Highlands, from whence it was taken
in the fifteenth century to the Highlands of Yemen, the southern
part of the Arabian peninsula. It has been introduced, and is
now extensively cultivated in British India, Java, Ceylon, the
Mauritius, Brazil, and the West Indies, but the quality is
inferior, which makes the climate of the Mocha coffee district of
importance, as peculiarly favourable to the plant. It grows there
on hills described by Niebuhr as being soaked with rain every
day from the beginning of June to the end of September, which is
carefully collected for the purpose of irrigation during the dry
season. Forskhal gives the following temperatures in the district:

Boit el Fakih March 16, 7 A.M. 76 deg. 1 P.M. 95 deg.
" " 18, " 77 " 95
Hodeida " 18, " 72 " 92-3/4
Bulgosa, a village
in the hills " 20, " 69-1/2 " 85-1/2

Boit el Fakih 10 P.M. 81 deg.
" " 81
Hodeida " 78
Bulgosa, a village
in the hills " 73

1225. Tea (_Thea Chinensis_). The plant is indigenous in China,
Japan, and Upper Assam. In the latter country, it has recently
been found in a wild state, and is in process there of extensive
cultivation. As the plant is hardy, its culture has very lately
been attempted in the South of France, and apparently with
complete success. A similar experiment on the burning plains of
Algeria completely failed, all the plants being killed by the
heat, notwithstanding every precaution. Tea was first introduced
into Europe by the Dutch in 1666. The leaves of the coffee-plant
have long been used as a substitute for tea, by the lower classes
in Java and Sumatra; and recently, Professor Blume, of Leyden,
exhibited samples of tea prepared from coffee-leaves, agreeing
entirely in appearance, odour, and taste, with the genuine Chinese
production.

1226. Sugar-cane (_Saccharum officinaram_), a species of
_Gramineæ_, occurs to some extent without the tropics, having been
cultivated centuries ago in Europe, as at present scantily in the
South of Spain. But it properly belongs to the torrid zone, and
has for its principal districts, the Southern United States, the
West Indies, Venezuela, Brazil, the Mauritius, British India,
China, the Sunda and Philippine Islands. The plant was found wild
in several parts of America on the discovery of that continent,
and occurs in a wild state on many of the islands of the Pacific.

1227. Vanilla (_Vanilla aromatica_), the fruit of which forms the
well-known aromatic, grows wild principally in Mexico.

1228. Peruvian bark (_Cinchona officinalis_), a forest tree, of
which there are several species, furnishing the valuable medicine
so called. It is exclusively confined to South America, and grows
chiefly on the Andes of Loxa and Venezuela.

1229. Pepper (_Piper nigrum_) belongs exclusively to the Malabar
coast, where it has been found wild, Sumatra, which produces the
greatest quantity, Borneo, the Malay peninsula, and Siam. Other
species of _Piperaceoe_ occur in tropical America.

1230. Cinnamon (_Laurus Cinnamomum_), a small tree yielding the
aromatic bark, is found native only in the island of Ceylon; but
another species occurs in Cochin China.

[Verse: "I am the true vine, and my Father is the husbandman."--JOHN XV.]

1231. Clove (_Myrtus caryophyllus_), an evergreen small tree, the
dried flower-buds of which form the celebrated aromatic, grows
naturally in the Moluccas, whence it has been conveyed to other
tropical districts. The island of Amboyna, one of that group, is
the principal seat of its cultivation. The lowest temperature
there is 72 degs.; the mean temperature of the year 82 degs.

1232. Nutmeg (_Myrstica moschata_) grows naturally in several
islands of the eastern archipelago, but is principally cultivated
in the Banda Isles.

Tropical families and forms successively vanish with an increase
of distance from the equator, and new phases of vegetation mark
the transition from hot to temperate climates. Vividly green
meadows, abounding with tender herbs, replace the tall rigid
grasses which form the impenetrable jungle; and instead of forests
composed of towering evergreen trees, woods of the deciduous
class appear, which cast their leaves in winter, and hybernate
in the colder season, the oak, ash, elm, maple, beech, lime,
alder, birch, and sycamore. The cultivation of the vine becomes
characteristic, with the perfection of the cereal grasses, and a
larger proportion of herbaceous annuals and cryptogamic plants.

1233. The vine (_Vitis vinifera_) is less impatient of a cold
winter than a cool summer. Hence its northern limit, which
coincides with lat. 47 deg. 30 min. on the west coast of France,
rises in the interior, where, though the winters are colder, the
summers are warmer, to lat. 49 degs., cuts the Rhine at Coblentz
in lat. 50 deg. 20 min., and ascends to 52 deg. 31 min. in Germany.

1234. Receding further from the equator, magnificent forests of
the fir and pine tribe prevail, as in the central parts of Russia,
on the southern shores of the Baltic, in Scandinavia, and North
America. But some of the cereals are no longer cultivatable, and
several timber-trees common to the temperate zone do not reach
its northern limits. Gradually all ligneous vegetation disappears
entirely as higher latitudes are approached, the woods having
first dwindled to mere dwarfs in struggling with the elements,
hostile to that state which nature destined them to assume. The
limit of the forests is a sinuous line running along the extreme
north of the old world; and extending from Hudson's Bay, lat.
60 deg., to the Mackenzie River, lat. 68 deg., and thence to
Behring's Strait. The dwarf birch (_Betula nana_), a mere bush, is
the last tree found on drawing near the eternal snow of the pole.
At the island of Hammerfest, lat. 70 deg. 40 min., near the North
Cape, it rises to about the height of a man, in sheltered hollows
between the mountains, its lower branches trailing on the ground,
affording a shelter to the ptarmigan. In the polar zone, some low
flowering annuals, saxifrages, ranunculi, gentians, chickweeds,
and others, flourish during the brief ardent summer; a few
perennials also accommodate themselves to the rigorous climate by
spreading laterally, never rising higher than four or five inches
from the ground; till finally no development of vegetable life is
met with, but lichens, and the microscopic forms that colour the
snow.

1235. In Europe, wheat ceases with a line connecting Inverness in
Scotland, lat. 58 deg., Drontheim in Norway, lat. 64 deg., and
Petersburgh in Russia lat. 60 deg. 15 min. Oats reach a somewhat
higher latitude. Barley and rye ascend to lat. 70 deg., but
require a favourable aspect and season to produce a crop.

1236. The northern limit of the growth of oak, lat. 61 deg.,
falls short of that of wheat. The oak makes a singular leap at
the confines of Europe and Asia, disappearing towards the Ural
mountains. This is the case also with the wild-nut and apple. The
oak and the wild-nut, however, re-appear suddenly in Eastern
Asia, on the banks of the Argoun and the Amour; and the apple
occurs again in the Aleutian Isles.

[Verse: "He hath made the earth by his power, he hath established the world by his wisdom, and hath stretched out the heavens by his discretion."--JEREMIAH X.]

1237. The following are the northern limits of several trees in
Scandinavia:

Lat.
Beech, _Fagus silvatica_ 60 deg. 0 min.
Hard Oak, _Quercus robur_ 61 " 0 "
Common Elm, _Ulmus campestris_ 61 " 0 "
Common Lime, _Tilia communis_ 61 " 0 "
Common Ash, _Fraxinus excelsior_ 62 " 0 "
Fruit trees 63 " 0 "
Hazel, Corylus, _avellana_ 64 " 0 "
Spruce Fir, _Abies excelsa_ 67 " 40 "
Service Tree, _Sorbus aucuparia_ 70 " 0 "
Scotch Fir, _Pinus silvestris_ 70 " 0 "
White Birch, _Betula alba_ 70 " 40 "
Dwarf Birch, _Betula nana_ 71 " 0 "

1238. Thus distinct vegetable regions are observed on passing
from south to north through different climatic zones, defined
as to their limits by the isothermal curves, and not by the
parallels of latitude. Similar changes of vegetation mark a
perpendicular transit through varying climates. A succession of
plants appear on the tropical mountains which rise above the snow
line, corresponding to those which are encountered in mean and
high latitudes. The higher we ascend, the more does the number of
the phænogamic class diminish in proportion to the cryptogamic,
till only members of the latter family are found, whose further
progress upward is arrested by the everlasting snow. The last
lichen met with by Saussure on Mont Blanc, _Silene acaulis_, was
also observed by M. Brevais in the neighbourhood of Bosekop, lat.
69 deg. 58 min. where it was vegetating on the seashore, shaded by
the last pines of Europe.

1239. Isolated mountains display to the best advantage the effort
of climatic change of vegetation.

1240. Etna is divided into three great regions: _La Regione
Culta_, or fertile region; _La Regione Sylvosa_, or woody region;
_La Regione Deserta_, the bare or desert region. But each of
these is susceptible of sub-divisions, defined by the presence of
certain families of plants, forming seven botanical zones.

1. The sub-tropical zone, which does not rise more than 100 feet
above the level of the sea, is characterised by the palm, banana,
Indian fig, sugar-cane, varieties of mimosa and acacia, which with
us are only found in conservatories.

2. The hilly zone, rises about 2,000 feet, characterised by the
orange, lemon, shaddock, maize, cotton, and grape plants.

3. The woody zone lies between the height of 2,000 and 4,000 feet,
where the cork-tree flourishes, several kinds of oak, the maple,
and enormous chestnuts.

4. The zone between the height of 4,000 and 6,000 feet is
distinguished by the beech, Scotch fir, birch, and, among small
plants, by clover, sandwort, chickweed, dock, and plantain.

5. The sub-alpine zone, between the elevation of 6,000 and 7,500
feet, produces the barberry, soap-wort, toad-flax, and juniper.

6. The zone between 7,500 and 9,000 feet, has almost all the
plants of the preceding, with the fleshy and jagged groundsel.

[Verse: "In the mountain of the height of Israel will I plant it; and it shall bring forth boughs, and bear fruit, and be a goodly cedar: and under it shall dwell all fowl of every wing; in the shadow of the branches thereof shall they dwell."--EZEKIEL XVII.]

7. The narrow zone between 9,000 and 9,200 feet, only produces a
few lichens, beyond which, there is complete sterility.

1241. The Peak of Teneriffe exhibits five botanical districts,
thus distinguished by Von Buch:

1. The region of Africa forms, 0--1,248 feet, comprising
palms, bananas, the sugar-cane, various species of arborescent
_Euphorbiæ_, _Mesembryanthema_, the _Dracæna_, and other
plants, whose naked and tortuous trunks, succulent leaves, and
bluish-green tints, are distinctive of the vegetation of Africa.

2. Region of Vines and Cereals, 1,248--2,748 feet, comprising also
the olive, and the fruit-trees of Europe.

3. Region of Laurels, 2,748--4,350 feet, including lauri of four
species, the wild olive, an oak, the iron-tree, the arbutus, and
other evergreens. The ivy of the Canaries and various twining
shrubs cover the trunks of the trees, and numerous species of fern
occur, with beautiful flowering plants.

4. Region of the Pines, 4,350--6,270, characterised by a vast
forest of trees resembling the Scotch fir, intermixed with juniper.

5. Region of the Retama, 6,270--11,061 feet, a species of broom,
which forms oases in the midst of a desert of ashes, ornamented
with fragrant flowers, and furnishing food to the goats, which
run wild on the Peak. A few gramineous and cryptogamic plants
are observed higher, but the summit is entirely destitute of
vegetation.

1242. There are many plants which can accommodate themselves to
the most diverse climates and localities; and therefore ascend
from the plains close to the boundary of vegetable life on the
highest mountains. But it is the general law in these cases for
such plants to be singularly modified in appearance and anatomical
structure as they ascend. The spring gentian, _Gentiana verna_,
is one of the exceptions, which Raymond found unaltered at all
heights in the Pyrenees.

1243. Trees, plants, and bushes, of humbler growth, which occur
on the plains and at great heights, are usually much smaller in
the latter situation. The leaves, and everything green about them,
dwindle with the increased elevation; and the pure, well defined
green is exchanged for an ill-defined light yellow. Singular
enough, those parts which seem most capable of resisting cold, as
the leaves and stalks, are uniformly subjected to a diminution of
their vital functions; while the flowers remain of the same size,
are never deformed, and become more dense and richer in their
colours. While the _Myosotis silvestris_ becomes stunted, its
flowers assume an intense blue--the admiration of the traveller.
The flowers of the pale primrose have a much deeper colour on the
top of the Faulhorn, while the plant itself is much smaller than
its congener on the Swiss plains. The observations of M. Parrot,
among others, are to this effect on the flora of the Caucasus, of
Ararat, the Swiss and Italian Alps, and the Pyrenees. The arctic
flora is similarly distinguished.

1244. The preceding references to different climatic states
are, however, perfectly inadequate to explain the phenomena of
vegetable distribution. While an analogy is often observable
between the plants of different regions under corresponding
circumstances of latitude, elevation, and soil, the species
are generally found to be different; and usually the botanical
character of countries not widely apart from each other, is
totally different, though under the same parallels.

[Verse: "From the rising of the sun, unto the going down of the same, the Lord's name is to be praised."--PSALM CXIII.]

1245. Some plants are entirely confined to one side of our
planet. The beautiful genus _Erica_, or heath, of which there are
upwards of 300 species, occurs with breaks over a narrow surface,
extending from a high northern latitude to the Cape of Good Hope.
But the whole continent of America does not contain a single
native specimen; nor has a _Poenia_ been found in it, except a
solitary one to the west of the Rocky Mountains. On the other
hand, the New World contains many families, as the _Cacti_, which
are not found naturally in the Old.

1246. Some plants occur in a single specific locality, frequently
a contracted area, and nowhere else. The beautiful _Disa
grandiflora_ is limited to a spot on the top of the Table Mountain
at the Cape; and the celebrated cedar of Lebanon appears to be
restricted in its spontaneous growth to the Syrian mountains. The
small island of St. Helena has an indigenous flora, with a few
exceptions different from that of the rest of the globe.

1247. Mountain chains of no great width very commonly divide a
totally distinct botany. There is a marked difference in the
vegetation of the Chilian and opposite side of the Andes, though
the climate as well as the soil is nearly the same, and the
difference of longitude very trifling. In North America, two
completely different classes of vegetation appear on the two sides
of the Rocky Mountains. A variety of oaks, palms, magnolias,
azaleas, and magnificent rhododendrons occur on the eastern side,
all of which are unknown on the western, the region of the giant
pine.

1248. The distinct vegetation possessed by various parts of
the globe, has led to its division into botanical kingdoms or
phyto-geographical regions, named in general after the genera
that are either peculiar to them, or predominant in them. The
arrangement of M. Schouw, which is usually adopted, discriminates
twenty-five great provinces of characteristic vegetation upon the
surface of the earth.

In constituting any portion of the globe into a phyto-geographical
region, M. Schouw has proceeded upon the following principles:--1.
That at least one-half of the species should be indigenous in it.
2. That a-quarter of the genera should also be peculiar to it,
or at least should have a decided maximum. 3. That individual
families of plants should either be exclusively confined to the
region, or have their maxima there.

1249. The phenomena of botanical geography, and the facts of
geology, are mutually illustrative. The existing dry land having
been upheaved above the waters at different epochs, it may be
reasonably inferred that each portion on its emergence received
a vegetable creation in harmony with its position. The ultimate
constitution of the general surface into different botanical
kingdoms would hence follow, each of which has preserved its
primitive features, while adjoining, and even far distant foci,
have to some extent intermingled their respective products, under
control of the natural agencies of diffusion.

1250. The agents that involuntarily officiate in the diffusion
of vegetable products are the atmosphere, the waters, and many
animals.

1. The impulsion of the atmosphere in its calmest state, is quite
sufficient to transport to considerable distances seeds furnished
with downy appendages or winglets, as is the case with many
plants, with the minute sporules of cryptogamia, which are light
as the finest powder. When ordinary breezes convey the sand-dust
of the Sahara a thousand miles or more from the desert, it may be
conceived that seeds, which are comparatively heavy, are borne far
from home by the hurricane. Two Jamaica lichens, which had never
been seen in France before, were found by De Candolle growing on
the coast of Brittany, the offspring of sporules which had been
swept over the Atlantic.

[Verse: "He shall come down like rain upon the mown grass, as showers that water the earth."--PSALM LXXII.]

2. The mountain torrent washes down into the valley the seeds
that have accidentally fallen into it, or have been swept away
by its overflows; and hence the plants of the High Alps occur on
the plains of Switzerland, which are entirely wanting in France
and Germany. Rivers answer the same purpose more extensively, and
also the oceanic currents. The nicker-tree, one of the leguminous
tribe, has been raised from seed borne across the Atlantic by the
Gulf stream.

3. Animals of the sheep and goat kinds, with the horse, deer,
buffalo, and others, widely disperse several species of plants,
the seeds of which, furnished with an apparatus of barbs and
hooks, adhere to their coating. Seeds also of various kinds pass
through the digestive organs of birds, uninjured as to their
vitality. The little squirrel buries the acorn in the ground for
winter provender, and sows an oak, if prevented from returning to
the spot.

1251. Plants capable of extended naturalisation, and serviceable
as articles of food or luxury, have been widely disseminated by
the human race in their migrations. The cerealia afford a striking
example. These important grasses known to the ancients, wheat,
barley, oats, and rye, were the gifts of the Old World to the New.
They are also importations into Europe; but the loose reports of
the ancients, and the diligent researches of the moderns, alike
leave us in ignorance of their native seat. Probability points to
the conclusion that they have spread from the neighbourhood of the
great rivers of Western Asia, the primitive location of the human
family; and it is not impossible that in that imperfectly explored
district, or further east on the Tartarian table-land, some of the
cereals may yet be found growing spontaneously. The first wheat
sown in North America, consisted of a few grains accidentally
found by a negro slave of Cortes, among the rice taken for the
support of his army. In South America the first wheat was brought
to Lima by one of the early colonists, a Spanish lady, Maria
d'Escobar. An ecclesiastic, Jose Rixi, was the first to sow it in
the neighbourhood of Quito.

1252. Maize, or Indian corn (_Zea mays_), has been dispersed in
the Old World from the New; and also a more important product, the
potato (_Solanum tuberosum_), the use of which now extends from
the extremity of Africa to Lapland. In Chili, the native country
of the plant, it occurs at present in a wild state. The Spaniards
imported it into Spain, and from thence it was communicated to
Italy. It was first made known in England at a subsequent period
from Virginia, having been received there from the Spanish
colonists in South America, as it is not a native of intervening
Mexico.

1253. The grape-vine, so extensively spread over Europe, is
probably not indigenous in any part of it. It chiefly owes its
diffusion there to the Romans, who received it from the Greeks,
to whom it most likely immediately came from the country between
the Black and Caspian Seas. The Romans introduced most of the
finer European fruit-trees, some from Africa, as the pomegranate,
but the great majority from Western Asia, as the orange, fig,
cherry, peach, apricot, apple, and pear. A variety of the plum,
the damson, or damascene, came from the neighbourhood of Damascus
during the Crusades. The name of the damask-rose points to the
importation of the plant from the same quarter into Europe.

[Verse: "To every thing there is a season, and a time to every purpose under heaven."--ECCLESIASTES III.]

The ocean as well as the land has different botanical regions; and
changes of the vegetation are observed with the depth analogous
to the variations of terrestrial plants with the height. Marine
vegetation seems to have its vertical extent determined by the
range of light in water, which varies with the power of the sun
and the transparency of the water.