apart from local phenomena, may see from the poles to the equator
organic life and vigor gradually augment with the augmentation of
vivifying heat. But, in the course of this progressive increase,
there are reserved to each zone its own peculiar beauties; to the
tropics, variety and grandeur of vegetable forms; to the north,
the aspect of its meadows and green pastures, and the periodic
reawakening of nature at the first breath of the mild air of
spring. Each zone, besides its own peculiar advantages, has its own
distinctive character.
In determining leading forms, or types, on the individual beauty,
the distribution, and the grouping of which the physiognomy of the
vegetation of a country depends, we must not follow the march of
systems of botany, in which from other motives the parts chiefly
regarded are the smaller organs of propagation, the flowers and the
fruit; we must, on the contrary, consider solely that which by its
mass stamps a peculiar character on the total impression produced, or
on the aspect of the country. Among the leading forms of vegetation
to which I allude, there are, indeed, some which coincide with
families belonging to the “natural systems” of botanists.
Such are the forms of bananas, palms, Casuarinæ, and Coniferæ. But
the botanic system divides many groups which the physiognomist is
obliged to unite.
[Illustration: Herbs, Useful and Medicinal
1, Myrtle; 2, Myrrh; 3, Hemlock; 4, Wormwood; 5, Frankincense; 6,
Hyssop]
We will begin with the palms, the loftiest and noblest of all
vegetable forms, that to which the prize of beauty has been assigned
by the concurrent voice of nations in all ages; for the earliest
civilization of mankind belonged to countries bordering on the region
of palms, and to parts of Asia where they abound. Their lofty,
slender, ringed, and, in some cases, prickly stems terminate in
aspiring and shining either fan-like or pinnated foliage. The leaves
are frequently curled, like those of some Gramineæ. Smooth, polished
stems of palms carefully measured by me had attained 192 English feet
in height. In receding from the equator and approaching the temperate
zone, palms diminish in height and beauty. The indigenous vegetation
of Europe only comprises a single representative of this form of
plants, the sea-coast dwarf-palm or Chamærops, which in Spain and
Italy extends as far north as the 44th parallel of latitude. The true
climate of palms has a mean annual temperature of 78°.2-81°.5 Fahr.
The date, which is much inferior in beauty to several other genera,
has been brought from Africa to the south of Europe, where it lives,
but can scarcely be said to flourish, in a mean temperature not
exceeding 59°-62°.4 Fahr.
In all parts of the globe the palm form is accompanied by that of
plantains or bananas; the Scitamineæ and Musaceæ of botanists,
Heliconia, Amomum, and Strelitzia. In this form, the stems, which
are low, succulent, and almost herbaceous, are surmounted by long,
silky, delicately veined leaves of a thin, loose texture, and bright
and beautiful verdure. Groves of plantains and bananas form the
ornament of moist places in the equatorial regions.
The form of Malvaceæ and Bombaceæ, represented by Ceiba,
Cavanillesia, and the Mexican hand-tree Cheirostemon, has enormously
thick trunks; large, soft, woolly leaves, either heart-shaped or
indented; and superb flowers, frequently of a purple or crimson hue.
It is to this group of plants that the baobab, or monkey bread-tree
(Adansonia digitata), belongs, which, with a very moderate elevation,
has a diameter of 32 English feet, and is probably the largest and
most ancient organic monument on our planet. In Italy the Malvaceæ
already begin to impart to the vegetation a peculiar southern
character.
The delicately pinnated foliage of the Mimosa form, of which Acacia,
Desmanthus, Gleditschia, Porleria, and Tamarindus are important
members, is entirely wanting in our temperate zone in the Old
Continent, though found in the United States, where, in corresponding
latitudes, vegetation is more varied and vigorous than in Europe. The
umbrella-like arrangement of the branches, resembling that seen in
the stone-pine in Italy, is very frequent among the Mimosas. The deep
blue of the tropic sky seen through their finely divided foliage has
an extremely picturesque effect.
The heath form belongs more especially to the African continent and
islands. Arborescent heaths, like some other African plants, extend
to the northern shores of the Mediterranean; they adorn Italy and
the cistus-covered grounds of the south of Spain. In the countries
adjoining the Baltic, and further to the north, the aspect of this
form of plants is unwelcome as announcing sterility.
The cactus form is almost exclusively American. Sometimes spherical,
sometimes articulated or jointed, and sometimes assuming the shape
of tall, upright polygonal columns resembling the pipes of an organ,
this group presents the most striking contrast to those of Liliaceæ
and bananas.
While the above-mentioned plants flourish in deserts almost devoid
of vegetation, the Orchideæ enliven the clefts of the wildest rocks
and the trunks of tropical trees blackened by excess of heat. This
form (to which the vanilla belongs) is distinguished by its bright
green succulent leaves, and by its flowers of many colors and strange
and curious shape, sometimes resembling that of winged insects, and
sometimes that of the birds which are attracted by the perfume of the
honey vessels. Such is their number and variety that, to mention only
a limited district, the entire life of a painter would be too short
for the delineation of all the magnificent Orchideæ which adorn the
recesses of the deep valleys of the Andes of Peru.
The Casuarina form, leafless, like almost all species of cactus,
consists of trees with branches resembling the stalks of our
Equisetums. It is found only in the islands of the Pacific and in
India, but traces of the same singular rather than beautiful type
are seen in other parts of the world.
As the banana form shows the greatest expansion, so the greatest
contraction of foliage is shown in Casuarinas, and in the form of
needle-trees (Coniferæ). Pines, thuias, and cypresses belong to this
form, which prevails in northern regions, and is comparatively rare
within the tropics: in Dammara and Salisburia the leaves, though
they may still be termed needle-shaped, are broader. In the colder
latitudes, the never-failing verdure of this form of trees cheers
the desolate winter landscape, and tells to the inhabitants of those
regions that when snow and ice cover the ground the inward life of
plants, like the Promethean fire, is never extinct upon our planet.
Like mosses and lichens in our latitudes, and like Orchideæ in the
tropical zone, plants of the Pothos form clothe parasitically the
trunks of aged and decaying forest trees: succulent herbaceous stalks
support large leaves, sometimes sagittate, sometimes either digitate
or elongate, but always with thick veins. The flowers of the Aroideæ
are cased in hooded spathes or sheaths, and in some of them when they
expand a sensible increase of vital heat is perceived. Stemless, they
put forth aerial roots. Pothos, Dracontium, Caladium, and Arum all
belong to this form, which prevails chiefly in the tropical world. On
the Spanish and Italian shores of the Mediterranean, Arums combine
with the succulent Tussilago, the acanthus, and thistles, which are
almost arborescent, to indicate the increasing luxuriance of southern
vegetation.
Next to the last-mentioned form, of which the Pothos and Arum are
representatives, I place a form with which, in the hottest parts of
South America, it is frequently associated--that of the tropical
twining rope-plants, or Lianes, which display in those regions, in
Paullinias, Banisterias, Bignonias, and Passifloras, the utmost vigor
of vegetation. It is represented to us in the temperate latitudes by
our twining hops and by our grapevines. On the banks of the Orinoco
the leafless branches of the Bauhinias are often between 40 and 50
feet long; sometimes they hang down perpendicularly from the high top
of the Swietenia, and sometimes they are stretched obliquely like the
cordage of a ship; the tiger-cats climb up and descend by them with
wonderful agility.
In strong contrast with the extreme flexibility and fresh,
light-colored verdure of the climbing plants, of which we have just
been speaking, are the rigid, self-supporting growth and bluish
hue of the form of the Aloes, which, instead of plaint stems and
branches of enormous length, are either without stems altogether or
have branchless stems. The leaves, which are succulent, thick, and
fleshy, and terminate in long points, radiate from a centre and form
a closely crowded tuft. The tall-stemmed aloes are not found in close
clusters or thickets like other social or gregarious plants or trees;
they stand singly in arid plains, and impart thereby to the tropical
regions in which they are found a peculiar, melancholy, and I would
almost venture to call it, African character. Taking for our guides
resemblance in physiognomy, and influence on the impression produced
by the landscape, we place together under the head of the Aloe form
(from among the Bromeliaceæ), the Pitcairnias, which in the chain
of the Andes grow out of clefts in the rocks; the great Pourretia
pyramidata (the Atschupalla of the elevated plains of New Granada);
the American Aloe (Agave); Bromelia aranas and Bromelia karatas;
from among the Euphorbiaceæ the rare species which have thick, short
candelabra-like divided stems; from the family of Asphodeleæ the
African Aloe and the Dragon tree (Dracæna draco); and lastly, from
among the Liliaceæ, the tall, flowering Yucca.
If the Aloe form is characterized by an almost mournful repose
and immobility, the form of Gramineæ, especially the physiognomy
of arborescent grasses, is characterized, on the contrary, by an
expression of cheerfulness and of airy grace and tremulous lightness,
combined with lofty stature. Both in the East and West Indies groves
of bamboo form shaded overarching walks or avenues. The smooth,
polished and often lightly waving and bending stems of these tropical
grasses are taller than our alders and oaks. The form of Gramineæ
begins even in Italy, in the Arundo donax, to rise from the ground
and to determine by height as well as mass the natural character and
aspect of the country.
The form of ferns, as well as that of grasses, becomes ennobled in
the hotter parts of the globe. Arborescent ferns, when they reach a
height of above forty feet, have something of a palm-like appearance;
but their stems are less slender, shorter, and more rough and scaly
than those of palms. Their foliage is more delicate, of a thinner and
more transparent texture, and the minutely indented margins of the
fronds are finely and sharply cut. Tree ferns belong almost entirely
to the tropical zone, but in that zone they seek by preference the
more tempered heat of a moderate elevation above the level of the
sea, and mountains two or three thousand feet high may be regarded
as their principal seat. In South America the arborescent ferns are
usually associated with the tree which has conferred such benefits on
mankind by its fever-healing bark. Both indicate by their presence
the happy region where reigns a soft, perpetual spring.
I will next name the form of Liliaceous plants (Amaryllis, Ixia,
Gladiolus, Pancratium), with their flag-like leaves and superb
blossoms, of which southern Africa is the principal country; also the
willow form, which is indigenous in all parts of the globe, and is
represented in the elevated plains of Quito (not in the shape of the
leaves, but in that of the ramification), by Schinus Molle; Mytraceæ
(Metrosideros, Eucalyptus, Escallonia myrtilloides); Melastomaceæ,
and the laurel form.
It is under the burning rays of a tropical sun that vegetation
displays its most majestic forms. In the cold north the bark of trees
is covered with lichens and mosses, while between the tropics the
Cymbidium and fragrant vanilla enliven the trunks of the Anacardia
and of the gigantic fig-trees. The fresh verdure of the Pothos leaves
and of the Dracontia contrasts with the many colored flowers of
the Orchideæ; Climbing Bauhinias, Passifloras, and yellow flowering
Banisterias twine round the trunks of the forest trees. Delicate
blossoms spring from the roots of the Theobroma, and from the thick
and rough bark of the Crescentias and the Gustavia. In the midst
of this profusion of flowers and fruits, and in the luxuriant
intertwinings of the climbing plants, the naturalist often finds it
difficult to discover to which stem the different leaves and flowers
really belong. A single tree adorned with Paullinias, Bignonias,
and Dendrobium forms a group of plants which, if disentangled and
separated, would cover a considerable space of ground.
In the tropics vegetation is generally of a fresher verdure, more
luxuriant and succulent, and adorned with larger and more shining
leaves than in our northern climates. The “social” plants, which
often impart so uniform and monotonous a character to European
countries, are almost entirely absent in the equatorial regions.
Trees almost as lofty as our oaks are adorned with flowers as large
and as beautiful as our lilies. On the shady banks of the Rio
Magdalena in South America, there grows a climbing Aristolochia
bearing flowers four feet in circumference which the Indian boys
draw over their heads in sport, and wear as hats or helmets. In the
islands of the Indian Archipelago the flower of the Rafflesia is
nearly three feet in diameter, and weighs above fourteen pounds.
THE GENESIS OF FLOWERS
--ALEXANDER S. WILSON
The flowers most generally known are brightly colored flowers adapted
for insect fertilization; only these require to attract insects,
which is the end served by the perfume and conspicuous coloring. Very
many plants, however, bear blossoms so small and obscurely colored
that they are either entirely overlooked or not reckoned as flowers
at all. The wind-fertilized flowers of the dock and nettle have no
occasion for the services of insects, and are destitute of honey,
odor, and brilliant petals. Still more insignificant in appearance
are the little self-fertilizing cleistogamic flowers, which, toward
the end of the season, are produced on the dog-violet. All three
kinds possess stamens and pistils, and are therefore recognized as
flowers by botanists. Besides stamens and pistils, which are the
essential organs of a flower, petals and sepals are usually present.
The petals collectively compose the corolla, the sepals the calyx;
both together being spoken of as the floral envelopes or perianth.
Occasionally, as in the ash, the flower is reduced to its essential
organs, the floral envelopes being absent. Plants bearing flowers,
whether with or without floral envelopes, are designated phanerogams
or flowering plants; they constitute the highest division of the
vegetable kingdom. Ferns and mosses, again, are examples of the
cryptogamic or flowerless class; they never bear flowers or seeds,
but are propagated by minute reproductive bodies termed spores.
This class is divided into thallophytes and vascular cryptogams. The
organization of a thallophyte is very simple; the plant body of a
fungus or sea-weed, for example, consists entirely of similar cells,
and externally shows no distinction into root, stem, and leaf. The
structure of a vascular cryptogam, such as a club-moss, horsetail,
or fern, is more complicated; both cells and vessels enter into the
composition of its tissues, and externally the distinction of stem
and leaf is apparent. Phanerogams also admit of a twofold division
into gymnosperms and angiosperms; conifers, cycads, and yews are
gymnospermous, having naked seeds, exposed either on the ends of
branches or on the surface of open scales. All ordinary flowering
plants produce their seed in the interior of a closed, ovary, as the
lower part of the pistil is called; from this peculiarity they are
termed angiosperms.
Only the remains of thallophytes have hitherto been discovered
in the oldest Palæozoic rocks. Vascular cryptogams appear in the
Silurian strata, attain their maximum in the Carboniferous age, and
in succeeding formations are gradually displaced by gymnosperms. The
latter occur as early as the Devonian period, but the prevailing type
of vegetation down to the close of Palæozoic time continued to be
cryptogamic. Angiosperms possibly existed as far back as the Permian
times, but it is only in the chalk that their remains begin to be
abundant; the vast majority of Mesozoic plants seem to have belonged
to the gymnospermous type. Plants with conspicuous flowers only date
from Tertiary times; they increase in number and importance as we
approach the present day.
Although the plants entombed in the rocks are only an inconsiderable
fraction of the numbers that formerly existed, the general succession
just indicated is fully made out, and as the palæontological evidence
accumulates it tends more and more to establish the view that colored
blossoms are, geologically speaking, of comparatively recent origin.
The vegetation of the earlier geological epochs was marked by a
singular uniformity of character; not only were there fewer species
than now, and these widely distributed over the globe, but the
monotonous green of Palæozoic and Mesozoic forests was unrelieved by
gay blossoms such as adorn our fields and orchards. We are indebted
to geology for another important fact; fossil plants occur which have
no near relatives in the existing flora. Intermediate forms which can
not properly be classified with any living family are met with; in
others the characters of several modern groups are blended. Although
these generalized forms rather upset our systems of classification,
they have an important bearing on the origin of living plants.
But what a different aspect, when the coal plants were growing in
primeval luxuriance, the landscape must have worn from that on which
we are accustomed to look! Odd, uncouth lepidodendra of arborescent
growth, huge reed-like calamites, gigantic ferns stretched in
interminable forests, clothed in one unvaried tint of sombre green.
How different is the scene which nature now presents!--mountains
glowing with the purple bloom of heather; hillsides where the furze
has spread its cloth of gold; meadows bright with daisies, ranunculi,
and cuckoo-flowers; banks where the wild thyme and bluebell grow! The
contrast affords a hint of the transformation in our world effected
by the introduction of flowers.
Our knowledge may not enable us to describe all the minute steps
which led to this remarkable change, but we can at least indicate
with great probability the nature of the process and some of the
agencies which contributed to bring about this result. To suppose
that each species of plant was independently created as we now see
it, implies not one creation merely, but many successive creations;
moreover, it leaves unexplained all the curious affinities which
exist among the members of the vegetable kingdom. The gradations of
structure, the geological succession, and the peculiarities of plant
growth are much more intelligible when we view the plants which now
inhabit the earth as the lineal descendants of those which lived
during the earlier ages of geology. From the nature of the case, the
theory of development does not admit of actual demonstration; still
the evidence in support of it is such that its advocates are entitled
to claim a verdict on the mass of indirect and circumstantial
evidence.
Among palæozoic cryptogams, we have evidence of the existence of
structures which, with comparatively little modification, might be
converted into what we now regard as flowers. The abundant remains
of lepidodendra in the Coal-measures testify to the important
place attained by the group of lycopods, or club mosses, in the
Palæozoic flora. To this family might very well have belonged
the archetype from which our modern blossom-bearing plants have
come. Our knowledge of this group is derived both from fossil
remains and from forms still extant. The selaginellas, so commonly
cultivated in greenhouses, are examples; also the little club moss
(Lycopodium selaginodes) of our highland moors. The last mentioned,
though a diminutive form, possesses special interest, being one of
the vascular cryptogams which produce two kinds of spores. This
heterosporous character was, however, a common feature of extinct
lycopods; both large and small spores have been detected in great
numbers in coal.