species and which has now grown to 12000, appear to belong to the Old
Continent: at least Decandolle described only 3590 American, whilst the
European, Asiatic, and African species amounted to 5093. This apparent
richness in Compositæ is, however, illusive, and considerable only in
appearance; the ratio or quotient of the family, (1/15 between the
tropics, 1/7 in the temperate zone, and 1/13 in the cold zone), shews
that even more species of Compositæ than Leguminosæ must hitherto have
escaped the researches of travellers; for a multiplication by 12 would
give us only the improbably low number of 144000 Phænogamous species.
The families of Grasses and Cyperaceæ give still lower results, because
comparatively still fewer of their species have been described and
collected. We have only to cast our eyes on the map of South America,
remembering the wide extent of territory occupied by grassy plains, not
only in Venezuela and on the banks of the Apure and the Meta, but also
to the south of the forest-covered regions of the Amazons, in Chaco,
Eastern Tucuman, and the Pampas of Buenos Ayres and Patagonia, bearing
in mind that of all these extensive regions the greater part have never
been explored by botanists, and the remainder only imperfectly and
incompletely so. Northern and Central Asia offer an almost equal extent
of Steppes, but in which, however, dicotyledonous herbaceous plants are
more largely mingled with the Gramineæ. If we had sufficient grounds
for believing that we are now acquainted with half the phænogamous
plants on the globe, and if we took the number of known species only at
one or other of the before-mentioned numbers of 160000 or 213000, we
should still have to take the number of grasses (the general proportion
of which appears to be 1/12), in the first case at least at 26000,
and in the second case at 35000 different species, which would give
respectively in the two cases only either 1/8 or 1/10 part as known.
The assumption that we already know half the existing species of
phænogamous plants is farther opposed by the following considerations.
Several thousand species of Monocotyledons and Dycotyledons, and
among them tall trees,--(I refer here to my own Expedition),--have
been discovered in regions, considerable portions of which had been
previously examined by distinguished botanists. The portions of the
great continents which have never even been trodden by botanical
observers considerably exceed in area those which have been traversed
by such travellers, even in a superficial manner. The greatest variety
of phænogamous vegetation, _i. e._ the greatest number of species on
a given area, is found between the tropics, and in the sub-tropical
zones. This last-mentioned consideration renders it so much the more
important to remember how almost entirely unacquainted we are, on
the New Continent, north of the equator, with the Floras of Oaxaca,
Yucatan, Guatimala, Nicaragua, the Isthmus of Panama, Choco, Antioquia,
and the Provincia de los Pastos;--and south of the equator, with the
Floras of the vast forest region: between the Ucayale, the Rio de la
Madera, and the Tocantin (three great tributaries of the Amazons), and
with those of Paraguay and the Provincia de los Missiones. In Africa,
except in respect to the coasts, we know nothing of the vegetation
from 15° north to 20° south latitude; in Asia we are unacquainted
with the Floras of the south and south-east of Arabia, where the
highlands rise to about 6400 English feet above the level of the
sea,--of the countries between the Thian-schan, the Kuenlün, and the
Himalaya, all the west part of China, and the greater part of the
countries beyond the Ganges. Still more unknown to the botanist are
the interior of Borneo, New Guinea, and part of Australia. Farther
to the south the number of species undergoes a wonderful diminution,
as Joseph Hooker has well and ably shewn from his own observation in
his Antarctic Flora. The three islands of which New Zealand consists
extend from 34-1/2° to 47-1/4° S. latitude, and as they contain,
moreover, snowy mountains of above 8850 English feet elevation, they
must include considerable diversity of climate. The Northern Island
has been examined with tolerable completeness from the voyage of Banks
and Solander to Lesson and the Brothers Cunningham and Colenso, and
yet in more than 70 years we have only become acquainted with less
than 700 phænogamous species. (Dieffenbach, Travels in New Zealand,
1843, vol. i. p. 419.) The paucity of vegetable corresponds to the
paucity of animal species. Joseph Hooker, in his Flora Antarctica,
p. 73-75, remarks that the “botany of the densely wooded regions of
the Southern Islands of the New Zealand groups and of Fuegia is much
more meagre not only than that of similarly clothed regions of Europe,
but of islands many degrees nearer to the Northern pole than these
are to the Southern one. Iceland, for instance, which is from 8 to 10
degrees farther from the equator than the Auckland and the Campbell
Islands, contains certainly five times as many flowering plants. In
the Antarctic Flora, under the influence of a cool and moist, but
singularly equable climate, great uniformity, arising from paucity
of species, is associated with great luxuriance of vegetation. This
striking uniformity prevails both at different levels, (the species
found on the plains appearing also on the slopes of the mountains), and
over vast extents of country, from the south of Chili to Patagonia,
and even to Tierra del Fuego, or from lat. 45° to 56°. Compare, on the
other hand, in the northern temperate region, the Flora of the South
of France, in the latitude of the Chonos Archipelago on the coast of
Chili, with the Flora of Argyleshire in Scotland in the latitude of
Cape Horn, and how great a difference of species is found; while in
the Southern Hemisphere the same types of vegetation pass through
many degrees of latitude. Lastly, on Walden Island, in lat. 80-1/2°
N., or not ten degrees from the North Pole of the earth, ten species
of flowering plants have been collected, while in the southernmost
islet of the South Shetlands, though only in lat. 63° S., only a
solitary grass was found.” These considerations on the distribution
of plants confirm the belief that the great mass of still unobserved,
uncollected, and undescribed flowering plants must be sought for in
tropical countries, and in the latitudes from 12° to 15° distant from
the tropics.
It has appeared to me not unimportant to show the imperfect state
of our knowledge in this still little cultivated department of
arithmetical botany, and to propound numerical questions in a more
distinct and determinate manner than could have been previously done.
In all conjectures respecting numerical relations we must seek first
for the possibility of deducing the lower or minimum limits; as in
a question treated of by me elsewhere, on the proportion of coined
gold and silver to the quantity of the precious metal fabricated in
other ways; or as in the questions of how many stars, from the 10th to
the 12th magnitude, are dispersed over the sky, and how many of the
smallest telescopic stars the Milky Way may contain. (John Herschel,
Results of Astron. Observ. at the Cape of Good Hope, 1847, p. 381.)
We may consider it as established, that if it were possible to know
completely and thoroughly by observation all the species belonging to
_one_ of the great families of phanerogamous or flowering plants, we
should learn thereby at the same time, approximatively, the entire
sum of _all_ such plants (including all the families). As, therefore,
by the progressive exploration of new countries we progressively and
gradually exhaust the remaining unknown species of any of the great
families, the previously assigned lowest limit rises gradually higher,
and since the forms reciprocally limit each other in conformity
with still undiscovered laws of universal organisation, we approach
continually nearer to the solution of the great numerical problem of
organic life. But is the number of organic forms itself a constant
number? Do new vegetable forms spring from the ground after long
periods of time, while others become more and more rare, and at last
disappear? Geology, by means of her historical monuments of ancient
terrestrial life, answers to the latter portion of this question
affirmatively. “In the Ancient World,” to use the remark of an eminent
naturalist, Link (Abhandl. der Akad. der Wiss. zu Berlin aus dem Jahr
1846, S. 322), “we see characters, now apparently remote and widely
separated from each other, associated or crowded together in wondrous
forms, as if a greater development and separation awaited a later age
in the history of our planet.”
[14] p. 19.--“_If the height of the aerial ocean and its pressure have
not always been the same._”
The pressure of the atmosphere has a decided influence on the form
and life of plants. From the abundance and importance of their leafy
organs provided with porous openings, plants live principally in and
through their surfaces; and hence their dependence on the surrounding
medium. Animals are dependent rather on internal impulses and stimuli;
they originate and maintain their own temperature, and, by means of
muscular movement, their own electric currents, and the chemical vital
processes which depend on and react upon those currents. A species
of skin-respiration is an active and important vital function in
plants, and this respiration, in so far as it consists in evaporation,
inhalation, and exhalation of fluids, is dependent on the pressure of
the atmosphere. Therefore it is that alpine plants are more aromatic,
and are hairy and covered with numerous pores. (See my work über die
gereizte Muskel- und Nervenfaser, Bd. ii. S. 142-145.) For according to
Zoonomic experience, organs become more abundant and more perfect in
proportion to the facility with which the conditions necessary for the
exercise of their functions are fulfilled,--as I have elsewhere shown.
In alpine plants the disturbance of their skin-respiration occasioned
by increased atmospheric pressure makes it very difficult for such
plants to flourish in the low grounds.
The question whether the mean pressure of the aerial ocean which
surrounds our globe has always been the same is quite undecided: we
do not even know accurately whether the mean height of the barometer
has continued the same at the same place for a century past. According
to Poleni’s and Toaldo’s observations, the pressure would have seemed
to vary. The correctness of these observations has long been doubted,
but the recent researches of Carlini render it almost probable that
the mean height of the barometer is diminishing in Milan. Perhaps
the phenomenon is a very local one, and dependent on variations in
descending atmospheric currents.
[15] p. 20.--“_Palms._”
It is remarkable that of this majestic form of plants,--(some of which
rise to more than twice the height of the Royal Palace at Berlin, and
to which the Indian Amarasinha gave the characteristic appellation of
“Kings among the Grasses”),--up to the time of the death of Linnæus
only 15 species were described. The Peruvian travellers Ruiz and Pavon
added to these 8 more species. Bonpland and I, in passing over a more
extensive range of country from 12° S. lat. to 21° N. lat., described
20 new species of palms, and distinguished as many more, but without
being able to obtain complete specimens of their flowers. (Humboldt
de distrib. geogr. Plantarum, p. 225-233.) At the present time, 44
years after my return from Mexico, there are from the Old and New
World, including the East Indian species brought by Griffith, above
440 regularly described species. The Enumeratio Plantarum of my friend
Kunth, published in 1841, had already 356 species.
A few, but only a few species of palms, are, like our Coniferæ,
Quercineæ, and Betulineæ, social plants: such are the Mauritia
flexuosa, and two species of Chamærops, one of which, the Chamærops
humilis, occupies extensive tracts of ground near the Mouth of the Ebro
and in Valencia; and the other, C. mocini, discovered by us on the
Mexican shore of the Pacific and entirely without prickles, is also a
social plant. While some kinds of palms, including Chamærops and Cocos,
are littoral or shore-loving trees, there is in the tropics a peculiar
group of mountain palms, which if I am not mistaken was entirely
unknown previous to my South American travels. Almost all species
of the family of palms grow on the plains or low grounds in a mean
temperature of between 22° and 24° Reaumur (81°.5 and 86°, Fahr.);
rarely ascending so high as 1900 English feet on the declivities of the
Andes: but in the mountain palms to which I have alluded, the beautiful
Wax-palm (Ceroxylon andicola), the Palmeto of Azufral at the Pass of
Quindiu (Oreodoxa frigida), and the reed-like Kunthia montana (Caña de
la Vibora) of Pasto, attain elevations between 6400 and 9600 English
feet above the level of the sea, where the thermometer often sinks
at night as low as 4°.8 and 6° of Reaumur (42°.8 and 45.°5, Fahr.),
and the mean temperature scarcely amounts to 11° Reaumur, or 56°.8
Fahrenheit. These Alpine Palms grow among Nut trees, yew-leaved species
of Podocarpus and Oaks (Quercus granatensis). I have determined by
exact barometrical measurement the upper and lower limits of the range
of the Wax-Palm. We first began to find it on the eastern declivity of
Andes of Quindiu, at the height of 7440 (about 7930 English) feet above
the level of the sea, and it extended upwards as far as the Garita del
Paramo and los Volcancitos, or to 9100 (almost 9700 English) feet:
several years after my departure from the country the distinguished
botanist Don Jose Caldas, who had been long our companion amidst the
mountains of New Granada, and who afterwards fell a victim to Spanish
party hatred, found three species of palms growing in the Paramo de
Guanacos very near the limits of perpetual snow; therefore probably at
an elevation of more than 13000 (13855 English) feet. (Semanario de
Santa Fé de Bogotá, 1809, No. 21, p, 163.) Even beyond the tropics,
in the latitude of 28° North, the Chamærops martiana reaches on the
sub-Himalayan mountains a height of 5000 English feet. (Wallich, Plantæ
Asiaticæ, Vol. iii. Tab. 211.)
If we look for the extreme geographical limits of palms, (which are
also the extreme climatic limits in all the species which inhabit
localities but little raised above the level of the sea), we see
some, as the date-palm, the Chamærops humilis, C. palmetto, and the
Areca sapida of New Zealand, advance far into the temperate zones of
either hemisphere, into regions where the mean temperature of the year
hardly equals 11°.2 and 12°.5 Reaumur (57°.2, and 60°.2 Fahrenheit).
If we form a series of cultivated plants or trees, placed in order of
succession according to the degree of heat they require, and beginning
with the maximum, we have Cacao, Indigo, Plantains, Coffee, Cotton,
Date-palms, Orange and Lemon Trees, Olives, Sweet Chestnuts, and
Vines. In Europe, date-palms (introduced, not indigenous) grow mingled
with Chamærops humilis in the parallels of 43-1/2° and 44°, as on the
Genoese Rivera del Ponente, near Bordighera, between Monaco and San
Stefano, where there is an assemblage of more than 4000 palm-stems; and
in Dalmatia round Spalatro. It is remarkable that Chamærops humilis
is abundant both at Nice and in Sardinia, and yet is not found in the
island of Corsica which lies between those localities. In the New
Continent, the Chamærops palmetto, which is sometimes above 40 English
feet high, only advances as far North as 34° latitude, a difference
sufficiently explained by the inflexions of the isothermal lines. In
the Southern hemisphere, in New Holland, palms, of which there are
very few, (six or seven species) only advance to 34° of latitude (see
Robert Brown’s general remarks on the Botany of Terra Australis, p.
45); and in New Zealand, where Sir Joseph Banks first saw an Areca
palm, they reach the 38th parallel. In Africa, which, quite contrary to
the ancient and still widely prevailing belief, is poor in species of
palms, only one palm, the Hyphæne coriacea, advances to Port Natal in
30° latitude. The continent of South America presents almost the same
limits in respect to latitude. On the eastern side of the Andes, in the
Pampas of Buenos Ayres and in the Cis-Plata province, palms extend,
according to Auguste de St.-Hilaire, to 34° and 35° S. latitude. This
is also the latitude to which on the western side of the Andes the Coco
de Chile (our Jubæa spectabilis?), the only Chilian palm, extends,
according to Claude Gay, being as far as the banks of the Rio Maule.
(See also Darwin’s Journal, edition of 1845, p. 244 and 256).
I will here introduce some detached remarks which I wrote in March,
1801, on board the ship in which we were sailing from the palmy shores
of the mouth of the Rio Sinu, west of Darien, to Cartagena de las
Indias.
“We have now, in the course of the two years which we have spent in
South America, seen 27 different species of palms. How many must
Commerson, Thunberg, Banks, Solander, the two Forsters, Adanson, and
Sonnerat, have observed in their distant voyages! Yet, at the present
moment, when I write these lines, our systems of botany do not include
more than from 14 to 18 systematically described species. In truth,
the difficulty of procuring the flowers of palms is greater than can
readily be imagined. We have felt it so much the more from having
especially directed our attention to Palms, Grasses, Cyperaceæ,
Juncaceæ, Cryptogamous Plants, and such other objects as have been
least studied hitherto. Most species of palms flower only once a
year, in the neighbourhood of the Equator in the months of January
and February. But how often is it impossible for travellers to be
precisely at that season in places where palms are principally found.
In many species of palms the flowers last only so few days that one
almost always arrives too late, and finds the fertilization completed
and the male blossoms gone. Frequently only three or four species of
palms are found in areas of 2000 square German geographical miles
(3200 English geographical square miles). How is it possible during
the short flowering season to visit the different places where palms
abound: the Missions on the Rio Caroni, the Morichales at the mouth
of the Orinoco, the valley of Caura and Erevato, the banks of the
Atabapo and the Rio Negro, and the side of the Duida Mountain? Add
to this the difficulty of reaching the flowers, when, in the dense
forests, or on the swampy river banks, (as on the Temi and Tuamini),
one sees them hanging from stems above 60 feet high, and armed with
formidable spines. A traveller, when preparing to leave Europe on an
expedition in which natural history is one of his leading objects,
flatters himself with the thoughts of shears or curved blades fastened
to long poles, with which he imagines he will be able to reach and
cut down whatever he desires; he dreams, too, of native boys, who,
with a cord fastened to their two feet, are to climb up the highest
trees at his bidding. But, alas! very few of these fancies are ever
realised; the great height of the blossoms renders the poles useless;
and in the missions established on the banks of the rivers of Guiana,
the traveller finds himself among Indians whose poverty, stoicism,
and uncultivated state, renders them so rich, and so free from wants
of every kind, that neither money nor other presents that can be made
to them will induce them to turn three steps out of their path. This
insurmountable apathy is the more provoking to a European, because
he sees the same people climb with inconceivable agility wherever
their own fancies lead them; for example, when they wish to catch
a parrot, or an iguana, or a monkey, which having been wounded by
their arrows saves himself from falling by holding on to the branches
with his prehensile tail. Even at the Havannah we met with a similar
disappointment. We were there in the month of January, and saw all the
trees of the Palma Real (our Oreodoxa Regia), in the immediate vicinity
of the city and on the public walks, adorned with snow-white blossoms.
For several days we offered the negro boys whom we met in the streets
of Regla and Guanavacoa two piastres for a single bunch of the blossoms
which we wanted, but in vain! Between the tropics men are indisposed
to laborious exertion, unless compelled by constraint or by extreme
destitution. The botanists and artists of the Royal Spanish Commission
for researches in Natural History, under the direction of Count Jaruco
y Mopor (Estevez, Boldo, Guio, and Echeveria),--acknowledged to us
that during several years they had not been able to obtain these
flowers for examination. These difficulties sufficiently explain what
would have been incomprehensible to me before my voyage, namely, that
although during our two years’ stay up to the present time, we have,
indeed, discovered more than 20 different species of palms, we have
as yet been only able to describe systematically 12. How interesting
a work might be produced by a traveller in South America who should
occupy himself exclusively with the study of palms, and should make
drawings of the spathe, spadix, inflorescence, and fruit, all of the
size of nature!” (I wrote this many years before the Brazilian travels
of Martius and Spix, and the admirable and excellent work of Martius on
Palms.) “There is considerable uniformity in the shape of the leaves
of palms; they are generally either pinnate (feathery, or divided like
the plume of a feather);--or else palmate or palmo-digitate (of a
fan-like form); the leaf-stalk (petiolus), is in some species without
spines, in others sharply toothed (serrato-spinosus). The form of the
leaf in Caryota urens and Martinezia caryotifolia, (which we saw on the
banks of the Orinoco and Atabapo, and again in the Andes, at the pass
of Quindiu, 3000 Fr. (3197 English) feet above the level of the sea),
is exceptional and almost unique among palms, as is the form of the
leaf of the Gingko among trees. The port and physiognomy of palms have
a grandeur of character very difficult to convey by words. The stem,
shaft, or caudex, is generally simple and undivided, but in extremely
rare exceptions divides into branches in the manner of the Dracænas,
as in Cucifera thebaica (the Doum-palm), and Hyphæne coriacea. It is
sometimes disproportionately thick (as in Corozo del Sinu, our Alfonsia
oleifera); sometimes feeble as a reed (as in Piritu, Kunthia montana,
and the Mexican Corypha nana); sometimes swelling towards the base (as
in Cocos); sometimes smooth, and sometimes scaly (Palma de covija o de
sombrero, in the Llanos); sometimes armed with spines (as Corozo de
Cumana and Macanilla de Caripe), the long spines being distributed with
much regularity in concentric rings.
“Characteristic differences are also furnished in some species by roots
which, springing from the stem at about a foot or a foot and a half
above the ground, either raise the stem as it were upon a scaffolding,
or surround it with thick buttresses. I have seen Viverras, and even
very small monkeys, pass underneath this kind of scaffolding formed
by the roots of the Caryota. Often the shaft or stem is swollen only
in the middle, being more slender above and below, as in the Palma
Real of the Island of Cuba. The leaves are sometimes of a dark and
shining green (as in the Mauritia and the Cocoa nut palm); sometimes
of a silvery white on the under side (as in the slender Fan-palm,
Corypha miraguama, which we found in the Harbour of Trinidad de Cuba).
Sometimes the middle of the fan or palmate leaf is ornamented with
concentric yellowish or bluish stripes like a peacock’s tail; as in
the thorny Mauritia which Bonpland discovered on the banks of the Rio
Atabapo.
“The direction of the leaves is a character not less important than
their form and colour. The leaflets (foliola), are sometimes arranged
like the teeth of a comb, set on in the same plane, and close to each
other, and having a very rigid parenchyma (as in Cocos, and in Phœnix
the genus to which the Date belongs); whence the fine play of light
from the sun-beams falling on the upper surface of the leaves (which
is of a fresher verdure in Cocos, and of a more dead and ashy hue in
the date palm); sometimes the leaves are flag-like, of a thinner and
more flexible texture, and curl towards the extremities (as in Jagua,
Palma Real del Sinu, Palma Real de Cuba, and Piritu dell’ Orinoco). The
peculiarly majestic character of palms is given not only by their lofty
stems, but also in a very high degree by the direction of their leaves.
It is part of the beauty of any particular species of palms that its
leaves should possess this aspiring character; and not only in youth,
as is the case in the Date-palm, but also throughout the duration of
the life of the tree. The more upright the direction of the leaves,
or, in other words, the more acute the angles which they form with the
upper part or continuation of the stem, the grander and more imposing
is the general character and physiognomy of the tree. How different are
the character and aspect given by the drooping leaves of the Palma de
covija del Orinoco y de los Llanos de Calabozo (Corypha tectorum); the
more nearly horizontal or at least less upright leaves of the Date and
Cocoa-nut palms; and the aspiring heavenward pointing branches of the
Jagua, the Cucurito, and the Pirijao!