Chapter XIII: Part 13

In proceeding from the consideration of these species to that of the
divisions established in the natural system according to an ideal
series of abstractions, we may direct our attention to genera or
races, to families, or even to still higher classes of division. There
are some genera, and even whole families, which exclusively belong to
certain zones; not merely because they can only thrive under a special
combination of climatic relations, but also because they first sprang
up within very circumscribed localities, and have been checked in
their migrations. The larger number of genera and families have,
however, their representatives in all regions of the earth, and at all
elevations. The earliest inquiries into the distribution of vegetable
forms had reference to genera alone, and are to be found in the
valuable work of Treviranus.[NJ] This method is, however, less
appropriate for yielding general results, than that which compares the
number of the species of each family, or the great leading divisions
(acotyledons, monocotyledons, and dicotyledons), with the sum total of
the phanerogamia. In the frigid zone, the variety of forms, or the
number of the genera, does not decrease in an equal degree with that
of the species, there being in these regions relatively more genera
and fewer species.[NK] The case is almost the same on the summits of
high mountain-chains, where are sheltered individual members of many
different genera which one would be disposed to regard as belonging
exclusively to the vegetation of the plain.

I have deemed it expedient to indicate the different points of view
from which the laws of the distribution of vegetable forms may be
considered. It is only when these points of view are confounded
together, that we meet with contradictions, which have been unjustly
attributed to uncertainty of observation.[NL] When expressions like
the following are employed: “This form, or this family diminishes as
it approaches towards the cold zone,” or “the true habitat of this
form is in such or such a parallel of latitude;” or “this is a
southern form,” or, again, “it predominates in the temperate zone;” it
should be definitely stated whether reference is made to the absolute
number of the species, and the proportion of their predominance
according to the increase or decrease of latitude; or whether the
meaning conveyed is, that a family, when compared with the whole
number of the phanerogamia of a flora, predominates over other
families of plants. The impression conveyed to the mind of the
predominance of forms, depends literally on the conception of relative
quantity.

Terrestrial physics have their numerical elements as well as the
cosmical system, and it is only by the united labours of botanical
travellers that we can hope gradually to arrive at a knowledge of the
laws which determine the geographical and climatic distribution of
vegetable forms. I have already observed that in the temperate zone of
the northern hemisphere, the Compositæ (Synanthereæ) and the Glumaceæ
(in which latter division I place the three families of the Gramineæ,
the Cyperoideæ, and the Juncaceæ) constitute the fourth part of all
phanerogamia. The following numerical relations are the result of my
investigations for seven great families of the vegetable kingdom in
one and the same temperate zone:

Glumaceæ ⅛ (Grasses alone ¹⁄₁₂) Compositæ ⅛ Leguminosæ ¹⁄₁₈ Labiatæ ¹⁄₂₄ Umbelliferæ ¹⁄₄₀ Amentaceæ (Cupuliferæ, Betulineæ, and Salicineæ) ¹⁄₄₅ Cruciferæ ¹⁄₁₉

The forms of organic beings are reciprocally dependent on one another.
Such is the unity of nature, that these forms limit each other in
obedience to laws which are probably connected with long periods of
time. When we have ascertained the number of the species on any
particular part of the earth’s surface belonging to one of the great
families of the Glumaceæ, the Leguminosæ, or the Compositæ, we may
with some degree of probability, form approximative conclusions
regarding the number of all the phanerogamia, as well as of the
species belonging to the other families of plants growing in the
country. The number of the Cyperoideæ determines that of the
Compositæ, and the number of the latter determines that of the
Leguminosæ; and these estimates, moreover, enable us to ascertain in
what classes and orders the Floras of a country are still incomplete,
teaching us what harvests may still be reaped in the respective
families, if we guard against confounding together very different
systems of vegetation.

The comparison of the numerical proportions of families in the
different zones which have as yet been well explored, has led me to a
knowledge of the laws which determine the numerical increase or
decrease of vegetable forms constituting a natural family, in
proceeding from the equator to the poles, when compared, for instance,
with the whole mass of phanerogamia peculiar to each zone. We must
here have regard not only to the direction, but also to the rapidity
or measure of the increase. We see the denominator of the fraction,
which expresses the ratio, increase or diminish. Thus, for instance,
the beautiful family of the Leguminosæ diminishes in proportion as it
recedes from the equinoctial zone to the north pole. If we find its
ratio for the torrid zone (from 0° to 10° of latitude) ⅒, we shall
have for the part of the temperate zone (lying between 45° and 52°)
¹⁄₁₈, and for the frigid zone (between 67° and 70° lat.) only ¹⁄₃₅.
The direction followed by the great family of the Leguminosæ (viz.,
increase towards the equator) is also that of the Rubiaceæ, the
Euphorbiaceæ, and especially the Malvaceæ. On the other hand, the
Gramineæ and the Juncaceæ (the latter more than the former), the
Ericeæ, and Amentaceæ, diminish towards the torrid zone. The
Compositæ, Labiatæ, Umbelliferæ, and Cruciferæ, diminish from the
temperate zone towards the pole and the equator, and the two latter
families most rapidly in the direction of the equatorial region;
whilst in the temperate zone the Cruciferæ are three times more
abundant in Europe than in the United States of North America. In
Greenland the Labiatæ are reduced to only one species, and the
Umbelliferæ to two, while the whole number of the phanerogamia still
amounts, according to Hornemann, to 315 species.

It must at the same time be observed that the development of plants of
different families, and the distribution of their forms, do not depend
alone on the geographical, or even on the isothermal latitude; the
quotients not being always equal on one and the same isothermal line
in the temperate zone, as for instance in the plains of America and in
those of the Old Continent. Within the tropics there is a very marked
difference between America, the East Indies, and the western coast of
Africa. The distribution of organic beings over the surface of the
earth does not depend solely on the great complication of thermic and
climatic relations, but also on geological causes which continue
almost wholly unknown to us, since they have been produced by the
original condition of the earth, and by catastrophes which have not
affected all parts of our planet simultaneously. The large
pachydermata are no longer found in the New Continent, while they
still exist under analogous climates in Asia and Africa. These
differences, instead of deterring us from the investigation of the
laws of nature, should rather stimulate us to study them in all their
intricate modifications.

The numerical laws of families, the frequently striking agreement
between the ratios, where the species constituting these families are
for the most part different, lead us into that mysterious obscurity
which envelopes everything connected with the fixing of organic types
in the different species of animals and plants, and with all that
refers to formation and development. I will take as examples two
neighbouring countries—France and Germany—which have both been long
since explored. In France many species of Gramineæ, Umbelliferæ,
Cruciferæ, Compositæ, Leguminosæ, and Labiatæ are wanting, which are
some of the commonest in Germany, and yet the ratios of these six
large families are almost identical in both countries. Their
relations, which I here give, are as follows:

Families. Germany. France.
Gramineæ. ¹⁄₁₃ ¹⁄₁₃
Umbelliferæ. ¹⁄₂₂ ¹⁄₂₁
Cruciferæ. ¹⁄₁₈ ¹⁄₁₉
Compositæ. ⅛ ⅐
Leguminosæ. ¹⁄₁₈ ¹⁄₁₆
Labiatæ. ¹⁄₂₆ ¹⁄₂₄

This correspondence in the number of species of one family compared to
the whole mass of the phanerogamia of Germany and France would not
exist, if the absent German species were not replaced in France by
other types of the same families. Those who delight in conjectures
respecting the gradual transformation of species, and who regard the
different parrots, peculiar to islands situated near each other, as
merely transformed species, will ascribe the remarkable uniformity
presented by the above numerical ratios to a migration of the same
species, which having been altered by climatic influences, continuing
for thousands of years, appear to replace each other. But why have our
common Heath, (Calluna vulgaris,) and our Oaks not penetrated to the
east of the Ural Mountains, and passed from Europe to northern Asia?
Why is there no species of the genus Rosa in the southern, and
scarcely any Calceolaria in the northern hemisphere? These are points
that cannot be explained by peculiarities of temperature. The present
distribution of forms (fixed forms of organization) is no more
explained by thermal relations alone, than by the hypothesis of
migrations of plants radiating from certain central points. Thermal
relations are scarcely sufficient to explain the phenomenon why
certain species have fixed limits beyond which they cannot pass,
either in the plains towards the pole, or in vertical elevation on the
declivities of mountains. The cycle of vegetation of each species,
however different may be its duration, requires a certain minimum of
temperature to enable it to arrive at the full stage of its
development.[NM] But all the conditions necessary to the existence of
a plant, either within its natural sphere of distribution or
cultivation—such as geographical distance from the pole, and elevation
of the locality—are rendered still more complicated by the difficulty
of determining the beginning of the thermic cycle of vegetation; by
the influence which the unequal distribution of the same quantity of
heat among days and nights succeeding each other in groups, exerts on
the irritability, the progressive development, and the whole vital
process; and lastly, by the secondary influence of the hygrometric and
electric relations of the atmosphere.

My investigations regarding the numerical laws of the distribution of
vegetable forms may, perhaps, at some future time, be applied
successfully to the different classes of vertebrate animals. The rich
collections of the Muséum d’histoire naturelle in the Jardin des
Plantes at Paris, contained in 1820, at a rough estimate, above 56,000
species of phanerogamic and cryptogamic plants in the herbariums,
44,000 insects (probably below the actual number, although they were
thus given me by Latreille), 2500 species of fishes, 700 reptiles,
4000 birds, and 500 mammalia. Europe possesses about 80 mammalia, 400
birds, and 30 reptiles; there are, therefore, five times as many birds
as mammalia in the northern temperate zone, (as there are in Europe
five times as many Compositæ as Amentaceæ and Coniferæ, and five times
as many Leguminosæ as Orchideæ and Euphorbiaceæ). In the southern
temperate zone the ratio of the Mammalia bears a sufficiently striking
accord with that of Birds, being as 1 : 4·3. Birds (and reptiles even
to a greater extent), increase more than mammalia in advancing towards
the torrid zone. We might be disposed to believe, from Cuvier’s
investigations, that this ratio was different in the earlier age of
our planet, and that the number of mammalia that perished by
convulsions of nature was much greater than that of birds. Latreille
has shown the different groups of insects that increase in advancing
towards the pole, or towards the equator, and Illiger has indicated
the native places of 3800 birds, according to the quarters of the
globe;—a far less instructive method than if they had been given
according to zones. We may easily comprehend how, on a given area, the
individuals of one class of plants or animals may limit each other’s
numbers, and how, after the long-continued contests and fluctuations
engendered by the requirements of nourishment and mode of life, a
condition of equilibrium may have been at length established; but the
causes which have determined their typical varieties, and have
circumscribed the sphere of the distribution of the forms themselves,
no less than the number of individuals of each form, are shrouded in
that impenetrable obscurity which still conceals from our view all
that relates to the beginning of things and the first appearance of
organic life.

If, therefore, as I have already observed at the beginning of this
illustration, we attempt to give an approximative estimate of the
_numerical limit_ (“le nombre limite” of the French mathematicians),
_below_ which we cannot place the sum of all the phanerogamia on the
surface of the earth; we shall find that the surest method will be by
comparing the known ratios of the families of plants with the number
of the species contained in our herbariums, or cultivated in large
botanical gardens. As I have just remarked, the herbariums of the
Jardin des Plantes at Paris were, in 1820, already estimated at 56,000
species. I will not hazard a conjecture as to the number that may be
contained in the herbariums of England, but the great Paris herbarium,
which Benjamin Delessert with the noblest disinterestedness has given
up to free and general use, was estimated, at the time of his death,
to contain 86,000 species, a number almost equal to that which
Lindley, even in 1835,[NN] regarded as the probable number of all the
species existing “on the whole earth.” Few herbariums are numbered
with care, according to a complete, severe, and methodical separation
of the different varieties; while, moreover, we often find no
inconsiderable number of plants wanting in the large so-called general
herbariums, which are contained in some of the smaller ones. Dr.
Klotzsch estimates the whole number of Phanerogamic plants in the
Great Royal Herbarium at Schöneberg, near Berlin, of which he is
curator, at 74,000 species.

Loudon’s useful work (_Hortus britannicus_) gives a general view of
the species which now are or recently have been, cultivated in English
gardens. The edition of 1832 enumerates, including indigenous plants,
exactly 26,660 Phanerogamia. We must not confound with this large
number of plants that either have been, or still are, cultivated in
Great Britain, “all the living plants which may simultaneously be
found in an individual botanic garden.” In this last respect the
Botanic Garden of Berlin has long been regarded as one of the richest
in Europe. The fame of its extraordinary riches rested formerly on a
mere approximative estimate of its contents, and, as my old friend and
fellow-labourer Professor Kunth, has very correctly remarked,[NO] “it
was only by the completion of a systematic catalogue, based on the
most careful examination of the species, that an actual enumeration
could be undertaken. This enumeration gave somewhat more than 14,060
species; and when we deduct from these 375 cultivated ferns, there
remain 13,685 Phanerogamia, among which there are 1600 Composite, 1150
Leguminosæ, 428 Labiatæ, 370 Umbelliferæ, 460 Orchideæ, 60 Palms, and
600 Grasses and Cyperaceæ. If we compare with these numbers the number
of species given in recent works, as, for instance, Compositæ
(according to Decandolle and Walpers), at about 10,000, Leguminosæ
8070, Labiatæ (Bentham) 2190, Umbelliferæ 1620, Grasses 3544, and
Cyperaceæ 2000,[NP] we shall perceive that the Botanic Garden at
Berlin cultivates only ⅐, ⅛, and ⅑ of the very large families
(Compositæ, Leguminosæ, and Grasses), and as many as ⅕ and ¼ of the
already described species belonging to the small families (Labiatæ and
Umbelliferæ). If we estimate the number of all the different species
of Phanerogamia _simultaneously_ cultivated in all the botanical
gardens of Europe at 20,000, we shall find, as they appear to
constitute about the eighth part of those already described and
contained in herbariums, that the whole number of Phanerogamia must
amount to nearly 160,000. This estimate need not be regarded as too
high, since scarcely the hundredth part of many of the larger
families, as, for instance, Guttifereæ, Malpighiaceæ, Melastomeæ,
Myrtaceæ, and Rubiaceæ, belong to our gardens.” If we take the number
(26,660 species), given in Loudon’s “Hortus Britannicus,” as the
basis, we shall find, from the well-grounded series of inferences
drawn by Professor Kunth, and which I borrow from his manuscript
notice above referred to, that the estimate of 160,000 will increase
to 213,000 species; and even this is still very moderate, since
Heynhold, in his “Nomenclator botanicus hortensis” (1846), estimates
the species of Phanerogamia already cultivated at 35,600. On the
whole, therefore,—and the conclusion is, at first sight, sufficiently
striking,—the number of species of Phanerogamia at present known by
cultivation in gardens, by descriptions, and in herbariums, is almost
greater than that of known insects. According to the average estimates
of several of the most distinguished entomologists, whose opinion I
have been able to obtain, the number of insects at present described,
or contained in collections without being described, may be stated as
between 150,000 and 170,000 species. The rich collection at Berlin
contains fully 90,000, among which there are about 32,000 beetles.
Travellers have collected an immense quantity of plants in remote
regions, without bringing with them the insects living upon them, or
in the neighbourhood. If, however, we limit these numerical estimates
to a definite portion of the earth’s surface that has been the best
explored in regard to its plants and insects, as, for instance,
Europe, we find the ratio between the vital forms of Phanerogamic
plants and those of insects changed to such a degree, that while
Europe counts scarcely 7000 or 8000 Phanerogamia, more than three
times that number of European insects are at present known. According
to the interesting contributions of my friend Dohrn in Stettin, more
than 8700 insects have already been collected from the rich fauna of
the neighbourhood, and yet there are still many MicroLepidoptera
wanting; while the number of Phanerogamia found there scarcely exceeds
1000. The Insect-fauna of Great Britain is estimated at 11,600. Such a
preponderance of animal forms will appear less surprising when we
remember that several of the large classes of insects live only on
animal substances, whilst others subsist on agamic plants (Fungi), and
even on those which are subterranean. Bombyx Pini, the Pine Spider,
the most destructive of all forest-insects, is infested, according to
Ratzeburg, by no less than thirty-five parasitical Ichneumonidæ.

These considerations have led us to the proportion borne by the number
of species growing in gardens to the gross number of those already
described and preserved in herbariums; it now remains for us to
consider the proportion of the latter to the conjectural number of
species existing on the whole earth, or, in other words, to test their
minimum by the relative numbers of the different families—_i. e._ by
variable _multipla_. A test of this kind gives, however, such low
results for the _lower_ amount, as plainly to show that even in the
large families, which appear to have been the most strikingly enriched
in recent times by the researches of descriptive botanists, our
knowledge is still limited to a very small portion of the treasure
actually existing. The _Repertorium_ of Walpers which completes
Decandolle’s _Prodromus_ of 1825 to 1846, gives 8068 species of the
family of the Leguminosæ. We may assume the mean ratio to be ¹⁄₂₁;
since it is ⅒ in the tropical zone, ¹⁄₁₈ in the middle temperate zone,
and ¹⁄₃₃ in the cold northern zone. The _described_ Leguminosæ would
therefore only lead us to assume that there were 169,400 species of
Phanerogamia existing on the earth, whereas the Compositæ, as already
shewn, testify to the existence of more than 160,000 known
Phanerogamia, _i. e._ such as have been described or are contained in
herbariums. This discrepancy is instructive, and will be further
elucidated by the following analogous considerations.

The larger number of the Compositæ, of which Linnæus knew only 785
species, and which have now increased to 12,000, appear to belong to
the Old Continent. At least Decandolle described only 3590 American,
while he estimated the European, Asiatic, and African species at 5093.
This abundance of Compositæ in our vegetable systems is however
deceptive, and only apparently considerable; for the quotient of this
family (which within the tropical zone is ¹⁄₁₅, in the temperate zone
⅐, and in the frigid zone ¹⁄₁₃) shows that more species of Compositæ
than of Leguminosæ have hitherto eluded the diligent research of
travellers; for even when multiplied by 12 we only obtain the
improbably small number of 144,000 for the sum total of the
Phanerogamia! The families of the Grasses and of the Cyperaceæ give
still lower results, because a proportionally smaller number of
species have been described and collected. We need only cast a glance
at the map of South America, and remember that the vast extent of
country occupied by the grassy plains of Venezuela the Apure and the
Meta, as well as to the south of the woody region of the Amazon, in
Chaco, in Eastern Tucuman, and in the Pampas of Buenos Ayres and
Patagonia, has either been very imperfectly or not at all explored in
relation to botany. Northern and Central Asia present an almost
equally extensive territory occupied by steppes; but here a larger
proportion of dicotyledonous plants is intermixed with the Gramineæ.
If we had sufficient grounds for believing that one-half of all the
phanerogamic plants existing on the surface of the earth are known,
and if we estimate this number at only 160,000 or at 213,000 known
species; we must give to the family of grasses, whose general ratio
appears to be ¹⁄₁₂, in the former case at least 26,000, and in the
latter 35,000 different species, of which in the first case ⅛, and in
the second ⅒ are known.

The following considerations oppose the hypothesis that we are already
acquainted with half the Phanerogamia on the earth’s surface. Several
thousand species of Monocotyledons and Dicotyledons, and among them
lofty arborescent forms, have recently been discovered (I would remind
the reader of my own expedition) in districts of a very large extent,
which had already been explored by distinguished botanists. Yet that
portion of the great continents which has never been visited by
botanical observers far exceeds the extent of the parts even
superficially traversed. The greatest variety of phanerogamic
vegetation, _i. e._ the greatest number of species on an equal area,
is to be met with in the tropical or subtropical zones. It is
therefore the more important to bear in mind that we are almost wholly
unacquainted, north of the equator, in the New Continent, with the
floras of Oaxaca, Yucatan, Guatimala, Nicaragua, the Isthmus of
Panama, the Choco, Antioquia, and the Province de los Pastos; while
south of the equator, we are equally ignorant of the floras of the
boundless forest-region between the Ucayale, the Rio de la Madura, and
the Toncantin (three mighty tributaries of the Amazon), as well as of
those of Paraguay and the Province de las Missiones. In Africa, we
know nothing of the vegetation of the whole of the interior, between
15° north and 20° south lat.; and in Asia we are unacquainted with the
floras of the south and south-east of Arabia, where the highlands rise
to an elevation of 6400 feet; as also with the floras between the
Thian-schan, the Kuen-Lün, and the Himalaya; those of Western China;
and those of the great portion of the countries beyond the Ganges.
Still more unknown to botanists are the interior portions of Borneo
and New Guinea, and of some districts of Australia. Further to the
south the number of the species decreases in a most remarkable manner,
as Joseph Hooker has ably shown, from his own observation, in his
_Antarctic Flora_. The three islands which constitute New Zealand
extend from 34½° to 47¼° of latitude, and as they have besides
snow-crowned mountains more than 8850 feet in height, they must
exhibit considerable differences of climate. The most northern island
has been explored with tolerable accuracy from the time of Banks and
Solander’s voyage (with Capt. Cook), to the visits of Lesson, the
brothers Cunningham, and Colenso; and yet in more than seventy years,
the number of Phanerogamia with which we have become acquainted is
below 700.[NQ] This paucity of vegetable species corresponds with the
paucity of animal forms. Dr. Joseph Hooker has observed that “Iceland,
proverbially barren as it is, and upon which no tree, save a few
stunted birches, is to be found, possesses five times as many
flowering plants as Lord Auckland’s group and Campbell’s Islands
together, although these are situated at from 8° to 10° nearer the
equator in the southern hemisphere. The antarctic flora is at once
characterised by uniformity and great luxuriance of vegetation, which
is attributable to the influence exerted by an uninterruptedly cool
and humid climate. In Southern Chili, Patagonia, and Tierra del Fuego
(from 45° to 56° lat.) this uniformity is strikingly manifested on the
mountains and their declivities no less than in the plains. How great
is the difference of species when we compare the flora of the south of
France, in the same latitude as the Chonos Islands off the coast of
Chili, with the Scottish flora of Argyleshire, in the parallel of Cape
Horn. In the southern hemisphere the same types of vegetation pass
through many degrees of latitude. In the regions near the north pole
ten flowering plants have been collected on Walden Island (80½° north
lat.), while there is scarcely a solitary grass to be met with in the
South Shetland Islands, although situated 63° south latitude.”[NR]
These considerations on the distribution of plants prove that the
great mass of the still unobserved, uncollected, and undescribed
phanerogamia belong to the tropical zone, and to the contiguous
regions extending from twelve to fifteen degrees from it.

I have deemed it not unimportant to draw attention to the imperfect
state of our knowledge in this slightly cultivated department of
numerical botany, and to treat such questions in a more definite
manner than has hitherto been possible. In all conjectures regarding
relative numbers, we must first examine the practicability of
obtaining the _lowest limit_; as in the question, of which I have
treated elsewhere, regarding the ratio of the gold and silver coined
to the quantity of the precious metals existing in a wrought state; or
as in the question of how many stars, from the tenth to the twelfth
magnitude, are scattered over the heavens, and how many of the
smallest telescopic stars may be contained in the Milky Way?[NS] It is
an established fact, that if it were possible to ascertain completely
by observation the number of species of the large phanerogamic
families, we should at the same time obtain an approximate knowledge
of the sum-total of all the phanerogamia on the surface of the earth
(that is, the numbers included in every family). The more therefore we
are enabled, by the progressive exploration of unknown districts,
gradually to determine the number of species belonging to any one
great family, the higher will be the gradual rise of the lowest limit,
and the nearer we shall arrive at the solution of a great numerical
vital problem, since the forms, in accordance with still unexplained
laws of universal organism, reciprocally limit each other. But is the
number of the organisms a constant number? Do not new vegetable forms
spring from the ground after long intervals of time, whilst others
become more and more rare, and finally disappear? Geology confirms the
latter part of this question by means of the historical memorials of
ancient terrestrial life. “In the primitive world,” to use the
expression of the intellectual Link,[NT] “elements remote from each
other blend together in wondrous forms, indicating, as it were, a
higher degree of development and articulation in a future period of
the world.”

Footnote 84:

p. 222—“_Whether the height of the aërial ocean and its pressure have
always been the same_.”

The pressure of the atmosphere has a decided influence on the form and
life of plants. This life, owing to the fulness and abundance of the
leafy organs provided with interstitial openings, is principally
directed _outwards_. Plants mainly live in and through their surfaces,
and hence their dependence on the surrounding medium. Animals are more
dependant on _internal_ stimuli; they generate and maintain their own
temperature, deriving from muscular movements their electric currents,
and the chemical vital processes which arise from and re-act upon
those currents. A kind of cutaneous respiration constitutes an active
vital function of plants, and depends, so far as it is an evaporation,
inhalation, and exhalation of fluids, on atmospheric pressure. Hence
Alpine plants are more aromatic and hirsute than others, and more
amply provided with numerous exhalants.[NU] Zoonomic experiments teach
us, as I have shown in another work, that organs are more abundant and
more perfectly developed in proportion to the facility with which
their functional requirements are fulfilled. The disturbance
occasioned in the respiration of their external integuments, by
increased barometric pressure, renders it, as I have elsewhere shewn,
very difficult for Alpine plants to thrive in the plain.

Whether the aërial ocean surrounding the earth has always exerted the
same mean pressure is a question wholly undecided. We do not even know
for certain whether the mean barometric height has remained the same
during a hundred years at any one given spot. According to the
observations of Poleni and Toaldo, this pressure appeared variable.
Doubts were long entertained regarding the accuracy of these views,
but the more recent investigations of the astronomer Carlini render it
almost probable that in Milan the mean barometric pressure is on the
decrease. Perhaps the phenomenon is very local, and dependent on
periodic variations in descending currents of air.

Footnote 85:

p. 223—“_Palms_.”

It is remarkable, that of this majestic form of plants—the Palms—some
of which rise to more than twice the height of the Royal Palace at
Berlin, and which the Indian, Amarasinha, has very characteristically
called “kings among grasses,”—only fifteen species had been described
up to the time of the death of Linnæus. The Peruvian travellers, Ruiz
and Pavon, added only eight; whilst Bonpland and myself, traversing a
greater extent of country, from 12° south lat. to 21° north lat.,
described twenty new species, and distinguished as many more which we
named, without however being able to procure their blossoms in a
perfect state.[NV] At present (forty-four years after my return from
Mexico) more than 440 species of palms, from both continents, have
already been scientifically described, including the East Indian
species arranged by Griffith. The “Enumeratio Plantarum” of my friend
Kunth, which appeared in 1841, contains no fewer than 356 species.

The very few palms belonging, like our Coniferæ, Quercineæ, and
Betulineæ, to social plants, are the Mauritian Palm (_Mauritia
flexuosa_), and the two species of Chamærops, of which the Chamærops
humilis covers whole tracts of land at the estuary of the Ebro and in
Valencia, while the other, Chamærops Mocini, which we discovered on
the Mexican shore of the Pacific, is entirely without prickles. In the
same manner as there are some species of palms, including Cocos and
Chamærops, which are peculiar to sea-coasts, so also is there a
certain group of Alpine palms belonging to the region of the tropics,
which, if I mistake not, was wholly unknown before my South American
journey. Almost all these species of the palm family grow in plains
and in a mean temperature of 81°.5 and 86° Fahr., seldom advancing
higher up the sides of the Andes than to 1900 feet. The beautiful wax
palm (_Ceroxylon andicola_), the Palmetto of Azufral at the Pass of
Quindiu, (_Oreodoxa frigida_), and the reed-like Kunthia montana
(_Caña de la Vibora_) of Pasto, all flourish at elevations varying
from 6400 to 9600 feet above the level of the sea, where the
thermometer frequently sinks in the night to 42°.8 and 45°.5 Fahr.,
and the mean temperature is scarcely 57° Fahr. These Alpine palms are
interspersed with nut-trees, yew-leaved species of Podocarpus, and
oaks, (_Quercus granatensis_). I have determined, by accurate
barometric measurements, the upper and lower limits of the wax palm.
We began to observe it first on the eastern declivity of the
Cordilleras of Quindiu, at an elevation of 7929 feet, from whence it
ascended to the Garita del Paramo, and Los Volcancitos, as high as
about 9700 feet. The distinguished botanist, Don José Caldas, who was
long our companion in the mountains of New Granada, and who fell a
victim to Spanish party hatred, found, many years after my departure
from the country, three species of palms in the Paramo de Guanacos, in
the immediate vicinity of the limit of perpetual snow, and therefore,
probably at an elevation of nearly 14,000 feet.[NW] Even beyond the
tropical region (in lat. 28°), Chamærops Martiana[NX] rises on the
advanced spurs of the Himalaya range to a height of 5000 feet.

When we consider the extreme geographical and, consequently, also the
climatic limits of palms at spots which are but little elevated above
the level of the sea, we find that some forms (the Date Palm,
_Chamærops humilis_, _Ch. palmetto_, and _Areca sapida_ of New
Zealand,) advance far within the temperate zone of both hemispheres,
to districts where the mean annual temperature scarcely reaches from
57° to 60° Fahr. If we form a progressive scale of cultivated plants
in accordance with the different degrees of heat they require, and
begin with the maximum, we have Cacao, Indigo, Bananas, Coffee,
Cotton, Date Palms, Orange and Lemon trees, Olives, Spanish Chesnuts,
and Vines. In Europe, Date Palms, together with Chamærops humilis,
grow in the parallels of 43½° and 44°, as, for instance, on the
Genoese Rivera del Ponente, near Bordighera, between Monaco and San
Stefano, where there is a palm grove, numbering more than 4000 trees;
also in Dalmatia, near Spalatro. It is remarkable that the Chamærops
humilis is of frequent occurrence in the neighbourhood of Nice and in
Sardinia, whilst it is not found in the Island of Corsica, lying
between the two. In the New Continent, the Chamærops palmetto, which
is sometimes more than 40 feet high, does not advance further north
than 34°; a circumstance that may be explained by the inflection of
the isothermal lines. In the southern hemisphere, Robert Brown[NY]
found that palms, of which there are only very few (six or seven)
species, advance as far as 34° in New Holland; while Sir Joseph Banks
saw an Areca, in New Zealand, as far as 38°. Africa, which, contrary
to the ancient and still extensively diffused opinion, is poor in
species of palms, exhibits only one palm (_Hyphæne coriacea_) which
advances south of the equator, only as far as Port Natal, in 30° lat.
The continent of South America presents almost the same limits. East
of the chain of the Andes, in the Pampas of Buenos Ayres, and in the
Cis-Plata province, palms extend, according to Auguste de
St.-Hilaire,[NZ] as far as 34° and 35°. The Coco de Chile, (our Jubæa
spectabilis?), the only species of palm indigenous in Chili, advances
on the western side of the chain of the Andes, according to Claude
Gay,[OA] to an equal latitude, viz., to the Rio Maule.

I will here subjoin the aphoristic observations which, in March, 1801,
I noted down while on board ship, at the moment we were leaving the
palm region surrounding the mouth of the Rio Sinu, west of Darien, and
were setting sail for Carthagena de Indias.

“In the space of two years, we have seen as many as 27 different
species of palms in South America. How many then must have been
observed by Commerson, Thunberg, Banks, Solander, the two Forsters,
Adanson, and Sonnerat, on their extensive travels! Yet, at the moment
I am writing, our vegetable systems recognise scarcely more than from
fourteen to eighteen methodically described species of palms. The
difficulties of reaching and procuring the blossoms of palms are, in
fact, greater than can well be conceived; and, in our own case, we
were made peculiarly sensible of this in consequence of our having
directed our attention especially to palms, grasses, cyperaceæ,
juncaceæ, cryptogamia, and numerous other subjects hitherto much
neglected. Most of the palms flower only once a year, and this period
near the equator is generally about the months of January and
February. How few travellers are likely to be in the region of palms
precisely during this season! The period of blossoming of particular
trees is often limited to a few days, and the traveller commonly
finds, on his arrival in the region of palms, that the blossoms have
passed away, and that the trees present only fructified ovaries and no
male flowers. In an area of 32,000 square miles, there are often not
more than three or four species of palms to be found. Who can
possibly, during the brief period of flowering, simultaneously visit
the various palm regions near the Missions on the Rio Caroni, in the
Morichales at the mouth of the Orinoco, in the valley of Caura and
Erevato, on the banks of the Atabapo and the Rio Negro, and on the
declivity of the Duida? There is, moreover, great difficulty when the
trees grow in thick woods or on swampy shores (as at the Temi and
Tuamini), in reaching the blossoms, which are often suspended from
stems formidably armed with huge thorns, and rising to a height of
between 60 and 70 feet. They who contemplate distant travels from
Europe for the purpose of investigating subjects of natural history,
picture to themselves visions of efficient shears and curved knives
attached to poles, ready for securing anything that comes in their
way; and of boys who, obedient to their mandates, are prepared, with a
cord attached to their feet, to climb the loftiest trees!
Unfortunately, scarcely any of these visions are ever realised; while
the flowers are almost unattainable, owing to the great height at
which they grow. In the missionary settlements of the river net-work
of Guiana, the stranger finds himself amongst Indians, who, rendered
rich and independent by their apathy, their poverty, and their
barbarism, cannot be induced either by money or presents to deviate
three steps from the regular path, supposing one to exist. This
stubborn indifference of the natives provokes the European so much the
more, from his being continually a witness of the inconceivable
agility with which they will climb any height when prompted by their
own inclination, as, for instance, in the pursuit of a parrot, an
iguana, or a monkey, which, wounded by their arrows, saves itself from
falling by its prehensile tail. In the month of January the stems of
the _Palma Real_, our _Oreodoxa Regia_, were covered with snow-white
blossoms, in all the most frequented thoroughfares of the Havannah,
and in the immediate vicinity of the city; but, although we offered,
for several days running, a couple of piastres for a single spadix of
the hermaphrodite blossoms to every negro boy we met in the streets of
Regia and Guanavacoa, it was in vain, for, in the tropics, no free man
will ever undertake any labour attended by fatigue unless he is
compelled to do so by imperative necessity! The botanists and painters
of the Royal Spanish Commission of Natural History under Count Don
Jaruco y Mopox (Estevez, Boldo, Guio, Echeveria), confessed to us
that, for several years, they had been unable to examine these
blossoms, owing to the absolute impossibility of obtaining them.

“After this statement of the difficulties attending their acquisition,
the fact of our being only able, in the course of two years,
systematically to describe twelve species of palms, although we had
discovered twenty species, may be understood; but I confess it would
hardly have been credible to me before I left Europe. How interesting
a work might be written on palms by a traveller, who could exclusively
devote himself to the delineation, in their natural size, of the
spathe, spadix, inflorescence and fruits!” (Thus I wrote many years
before the Brazilian travels of Martius and Spix, and the appearance
of the admirable work on Palms by the former.)

“There is much sameness in the form of the leaves, which are either
feathery (pinnata), or fan-like (palmo-digitata); the leaf-stalk
(petiolus) is either without thorns or is sharply serrated
(_serrato-spinosus_). The leaf-form of _Caryota urens_ and _Martinezia
caryotifolia_, which we saw on the banks of the Orinoco and the
Atabapo, and subsequently in the Andes, at the pass of Quindiu, as
high as 3200 feet above the level of the sea, is almost as peculiar
among palms as is the leaf-form of the Gingko among trees. The habitus
and physiognomy of palms are expressive of a grandeur of character
which it is difficult to describe in words. The stem (_caudex_) is
simple, and very rarely divided into branches after the manner of the
Dracæna, as in Cucifera thebaica (the Doom Palm), and in Hyphæne
coriacea. It is sometimes disproportionately thick, as in Corozo del
Sinu, our Alfonsia oleifera; of a reed-like feebleness, as in Piritu,
(_Kunthia montana_), and the Mexican Corypha nana; of a somewhat
fork-like and protuberant form towards the lower part, as in Cocos;
sometimes smooth and sometimes scaly, as in the Palma de Covijaó de
Sombrero, in the Llanos; or, lastly, prickly, as in Corozo de Cumana
and Macanilla de Caripe, having the thorns very regularly arranged in
concentric rings.

“Characteristic differences also manifest themselves in the roots,
which, in some cases, project about a foot or a foot and a half from
the ground, raising the stem on a scaffolding, as it were, or coiled
round it in a padded-like roll. I have seen viverras and even very
small monkeys pass under the scaffolding formed by the roots of the
Caryota. Occasionally the stem is swollen only in the middle, being
smaller above and below, as in the Palma Real of the island of Cuba.
The green of the leaves is either dark and shining, as in Mauritia
Cocos, or of a silvery white on the under side, as in the slender
fan-palm, _Corypha Miraguama_, which we saw in the harbour of Trinidad
de Cuba. Sometimes the middle of the fan-like leaf is adorned with
concentric yellow and blue stripes, in the manner of a peacock’s tail,
as in the prickly Mauritia, which Bonpland discovered on the Rio
Atabapo.

“The direction of the leaves is a no less important characteristic
than their form and colour. The leaflets (foliola) are either ranged
in a comb-like manner close to one another, with a stiff parenchyma
(as in _Cocos Phœnix_), to which they owe the beautiful reflections of
solar light that play over the surface of the leaves, which shine with
a brilliant verdure in _Cocos_, and with a fainter and ashy-coloured
hue in the date-palm; or sometimes the foliage assumes a reed-like
appearance, having a thinner and more flexible texture, and being
curled near the extremity (as in _Jagua_, _Palma Real del Sinu_,
_Palma Real de Cuba_, and _Piritu del Orinoco_). This direction of the
leaves, together with the lofty stem, gives to the palms their
character of high majesty. It is a characteristic of the
physiognomical beauty of the palm that its leaves are directed
aspiringly upwards throughout the whole period of its duration, (and
not only in the youth of the tree, as is the case with the Date-Palm,
which is the only one introduced into Europe.) The more acute the
angle made by the leaves with the upper part of the stem (that is, the
nearer they approach the perpendicular,) the grander and nobler is the
form of the tree. How different is the aspect of the pendent leaves of
the _Palma de Covija del Orinoco y de los Llanos de Calabozo_ (Corypha
tectorum), from the more horizontal leaves of the Date and Cocoa-nut
palms, and the lofty heavenward-pointing branches of the _Jagua_, the
_Cucurito_, and _Pirijao_.

“Nature seems to have accumulated all the beauties of form in the
Jagua palm, which, intermingled with the Cucurito or Vadgihai, whose
stem rises to a height of 80 or even more than 100 feet, crowns the
granite rocks at the cataracts of Atures and Maypures, and which we
also occasionally saw on the lonely banks of the Cassiquiare. Their
smooth and slender stems rise to a height of from 64 to 75 feet,
projecting like a colonnade above the dense mass of the surrounding
foliage. These aërial summits present a marked and beautiful contrast
with the thickly-leaved species of _Ceiba_, and with the forest of
_Laurineæ_, _Calophyllum_, and the different species of _Amyris_ which
surround them. Their leaves, which seldom exceed seven or eight in
number, incline vertically upwards to a height of 16 or 17 feet, and
are curled at the extremities in a kind of feathery tuft. The
parenchyma of the leaf is of a thin grass-like texture, causing the
leaflets to wave with graceful lightness on the gently oscillating
leaf-stalk. The floral buds burst forth, in all species of palms, from
the stem immediately beneath the leaves; and the mode in which this
takers place modifies their physiognomical character. Thus in some, as
in _Corozo del Sinu_, the sheath is perfectly erect, and the fruit
rises like a thyrsus, resembling the fruits of the Bromelia. In the
greater number, the sheaths, which in some species are smooth, and in
others very prickly and rough, incline downwards. In some, again, the
male blossoms are of a dazzling white, and it may then be seen shining
from a great distance; but in most species of palms they are yellow,
closely compressed, and of an almost faded appearance, even when they
first burst from the spathe.

“In palms with feathery leaves the leaf-stalks either burst from the
dry, rough, ligneous portion of the stem (as in _Cocos_, _Phœnix_,
_Palma Real del Sinu_), or there rises in the rough part of the stem a
grass-green, smooth, and thinner shaft, like one column above another,
from which the leaf-stalk springs, as in _Palma Real de la Havana_,
_Oreodoxa regia_, which excited the admiration of Columbus. In the
fan-palms (_foliis palmatis_), the leafy crown often rests on a layer
of dry leaves, which imparts to the tree a character of melancholy
solemnity and grandeur (as in _Moriche_, _Palma de sombrero de la
Havana_). In some umbrella-palms, the crown consists of a very few
scattered leaves, raised on slender stalks (as in _Miraguama_).

“The form and colour of the fruit also present more variety than is
generally supposed to be the case in Europe. _Mauritia flexuosa_ has
egg-shaped fruits, whose smooth, brown, and scaly surface gives them
the appearance of young pine cones. How great is the difference
between the large triangular cocoa-nut, the berry of the date, and the
small stone-fruit of the Corozo! But of all the fruits of the palm,
none can be compared for beauty with those of the Pirijao (_Pihiguao_)
of San Fernando de Atabapo and of San Balthasar. They are oval, and of
a golden colour (one-half being of a purplish red); are mealy, without
seed, two or three inches in thickness, and hang in clusters like
grapes from the summits of their majestic palm-trunks.” I have already
spoken in the earlier part of this work of these beautiful fruits, of
which there are seventy or eighty clustered together in one bunch, and
which can be prepared in a variety of ways like bananas and potatoes.

The spathe enclosing the blossom bursts suddenly open in some species
of palms, with an audible report. Richard Schomburgk has like myself
observed this phenomenon[OB] in the flowering of the Oreodoxa
oleracea. This first opening of the blossoms of the palm accompanied
with noise, reminds us of Pindar’s Dithyrambus on Spring, and of the
moment when in the Argive Nemæa, “the first opening shoot of the
date-palm announces the coming of balmy spring.”[OC]

Palms, bananas, and arborescent ferns constitute three forms of
especial beauty peculiar to every portion of the tropical zone;
wherever heat and moisture co-operate, vegetation is most exuberant
and vegetable forms present the greatest diversity. Hence South
America is the most beautiful portion of the palm world. In Asia the
palm form is rare, in consequence perhaps of a considerable part of
the Indian continent beneath the equator having been destroyed and
covered by the ocean in some earlier revolution of our planet. We know
scarcely anything of the African palms between the Bay of Benin and
the coast of Ajan; and we are, generally speaking, as already
observed, acquainted with only a very small number of African
palm-forms.

Palms, next to Coniferæ, and some species of Eucalyptus belonging to
the family of the Myrtaceæ, afford examples of the loftiest growth.
Stems of the Cabbage-palm (_Areca oleracea_) have been seen from 160
to 170 feet in height.[OD] The Wax-palm, our Ceroxylon andicola, which
we discovered in the Montaña de Quindiu on the side of the Andes,
between Ibague and Carthago, attains the enormous height of 180 to 190
feet. I was able to make an accurate measurement of the trunks of some
of these trees, which had been felled in the woods. Next to the
Wax-palm, the Oreodoxa Sancona, which we found in flower in the valley
of Cauca, and which affords a very hard and admirable wood for
building, appeared to me to be the highest of all American palms. The
fact, that notwithstanding the enormous mass of fruit yielded by some
single palms, the number of individuals of each species growing wild
is not very considerable, can only be explained by the frequent
abortive development of the fruit, and by the voracity of the enemies
by whom they are assailed from all classes of animals. In the basin of
the Orinoco, however, whole tribes find the means of subsistence for
many months together in the fruit of the palm. “In palmetis, Pihiguao
consitis, singuli trunci quotannis fere 400 fructus ferunt pomiformes,
tritumque est verbum inter Fratres S. Francisci, ad ripas Orinoci et
Guainiæ degentes, mire pinguescere Indorum corpora, quoties uberem
Palmæ fructum fundant.”[OE]

Footnote 86:

p. 224—“_From the earliest infancy of human civilization_.”

We find, as far as history and tradition extend, that the Banana has
constantly been cultivated in all continents within the tropical zone.
The fact of African slaves having, in the course of centuries, brought
some varieties of the Banana fruit to America is as certain as that of
the cultivation of this vegetable product by the natives of America
prior to its discovery by Columbus. The Guaikeri Indians in Cumana
assured us that on the coast of Paria, near the Golfo Triste, the
Banana will occasionally produce germinating seeds, if the fruit be
suffered to ripen on the stem. It is from this cause, that wild
Bananas are occasionally found in the recesses of the forests, in
consequence of the ripe seeds being scattered abroad by birds. At
Bordones also, near Cumana, perfectly formed and matured seeds have
been occasionally found in the fruit of the Banana.[OF]

I have already remarked, in another work,[OG] that Onesicritus and
other companions of the great Macedonian, make no mention of high
arborescent ferns, although they speak of the fan-leaved umbrella
palms and of the tender evergreen verdure of the banana-plantations.
Among the Sanscrit names given by Amarasinha for the Banana (the
_Musa_ of botanists) we find _bhanu-phala_ (sun-fruit),
_varana-buscha_, and _moko_. Phala signifies fruit generally. Lassen
explains Pliny’s words (xii. 6), “Arbori nomen palæ, pomo arienæ,” to
this effect, that “The Roman mistook the word _pala_, fruit, for the
name of the tree, whilst _varana_, changed in the mouth of a Greek to
_ouarana_, was transformed into _ariena_. The Arabic _mauza_, our
Musa, may have been formed from _moko_. The Bhanu fruit seems to
approach to Banana fruit.”[OH]

Footnote 87:

p. 224—“_Form of the Malvaceæ_.”