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Ferns and Tree Ferns
The earliest traces of
vegetable life yet discovered in the most ancient fossiliferous rocks,
consist of fragments of sea-weed, accompanying graptolites, or sea-pens,
in the anthracite beds of the Silurian system, which in all probability
owed their origin to the decomposition of plants of this description, once
forming submarine meadows, where zoophytes nestled and trilobites swam. So
far as geological investigation has yet gone, it does not appear that a
terrestrial flora flourished on the shores of the primeval sea till the
age of the old red sandstone, when fishes of singular conformation,such as
the pterichthys, with its wing-like arms, disported in the waters. The
first indications of land plants are found in the lower beds of that
series of rocks, and consist of the remains of lycopodiums or club -
mosses, of tree-ferns, and the wood of coniferous trees, resembling the
modern araucaria, or Norfolk Island pine. The deposits of this era, both
in Ireland and Scotland, have yielded fragments of the fronds or leaves of
a tree-fern named Cyclopteris Hibernica, which disappeared before the dawn
of the carboniferous period, when, as we have seen, ferns and their allies
prevailed over a great portion of the surface of the earth, laying up, for
the use of distant ages, beds of coal, deriving their carbon from the
carbonic acid gas floating in the then existing atmosphere, and their
hydrogen from the decomposition of water, which, descending in rain,
mottled, with its drops, the yielding sand; while, upon the same shores,
the ripple of the rising and receding tide was tracing the curving and
anastomosing lines now so frequently observable on slabs of building and
paving stones. We thus learn, from the traces of life-history in the
ancient rocks, that, however varied the forms of animals and plants
existing in successive geological epochs, the conditions of life have been
uniform in all ages. Geology teaches us, to use the words of Professor
Owen, that "the globe allotted to man has revolved in its orbit through a
period of time so vast, that the mind, in the endeavour to realise it, is
strained by an effort like that by which it strives to conceive the space
dividing the solar system from the most distant nebulae." The pages of the
rocky science bear evidence not less equivocal to the conditions in which
organised beings existed upon the earth's surface during all the different
eras which it is the province of the geologist to investigate and define.
The light and heat of the sun reached the earth through an atmosphere not
different from that by which the surface of the globe at present receives
the same vivifying influences. The eye of the trilobite was constructed
upon the same optical principles, and adapted to the same conditions of
light and vision, as the eye of the existing crustacean and insect.
Vaporised moisture ascended from earth and sea, and became condensed in
the atmosphere, whence it was precipitated in fertilising showers of rain.
These showers have not only left, in the strata of successive systems, the
casts of rain-marks, indicating by their slope or shape the direction from
which they were blown by the wind; but the little rills formed by the
gathering drops, as they rolled along the surface of the sand or mud, have
also had their traces preserved—a phenomenon which has been detected in
Lower Canada in rocks so early as those of the old red sandstone,
contemporaneous with the first vestiges of terrestrial vegetation, and
recording the most ancient showers of rain of which we have any geological
memorial. The study of fossil botany shews, in like manner, that the
extinct vegetables of the palæozoic flora must have existed in conditions
of the air and earth, such as are still essential to the growth and
development of the plant. But while we thus derive from the rocks
incontestable proofs of the uniformity of the laws of nature throughout
prolonged and successive epochs, we are called to contemplate an
astonishing variety in the productions existing at different times in the
organised world. Entire races of animals and plants were again and again
extinguished, and replaced by new tribes, which have no specific
representatives in our present flora and fauna. Yet amidst boundless
diversity of form and function in the animal and vegetable kingdoms,
viewed along the entire course of creation, we are able to discover an
undeviating adherence to typical unity in the glorious plan of the
Almighty's handiwork. In evolving this great central principle of the
organic creation, science occupies its true position as the handmaid of
religion. From the realms of living nature, and the records of past
creations, it brings, as a tribute to the altar of the Christian faith, a
confirmation of the personal unity of the adorable " I AM," revealed in
the pages of eternal truth ; and in demonstrating the unity of the
Creator, by tracing through creation the archetypical idea which must have
dwelt for ever in the Divine Mind, it has also enriched natural theology
with fresh and vivid illustrations of the wisdom and goodness of God, in
adapting the typical forms of animals and plants to an endless diversity
of benevolent purposes. The science of geology is a history of successive
miracles of creation. The subtle sceptic who demanded the testimony of
experience to convince him of the possibility of a miracle, lived before
geology had borne evidence on the subject such as no rational man will be
hardy enough to gainsay. It was a shrewd remark of Hugh Miller's —"Hume is
at length answered by the severe truths of the stony science. He was not,
according to Job, in league with the stones of the field,' and they have
risen in irresistible warfare against him in the Creator's behalf."
Ferns, and tree-ferns, have
descended to our time from the remotest period of vegetable life, although
they nowhere exist in such abundance as they appear to have done during
the carboniferous era, when, although the vegetation was scanty in the
variety, it was profuse in the number, of species. Of 500 plants
discovered in the coal measures, 346 were ferns and their allies, nearly
300 being true ferns. Many of these are preserved in the shales of the
coal mines, with their fossilised fronds and minute venation as distinctly
defined as if the plants had been laid up in a botanist's herbarium. In
the mines of Bohemia, Dr Buck-land found the ferns and other vegetable
remains of the coal exceeding in beauty the most elaborate imitations of
living" foliage upon the painted ceilings of Italian palaces. The roofs of
the mines were covered as with a canopy of gorgeous tapestry, enriched
with festoons of most graceful foliage, flung in wild, irregular profusion
over every portion of the surface, the effect being heightened by the
contrast between the shining black colour of the coal plants and the light
hues of the rocks to which they were attached. The ferns of the English
coal-fields number about 140. The existing British species of ferns,
including varieties raised to the rank of species, are under 50. In
tropical countries, especially those having an insular climate, such as St
Helena and the Society Islands, ferns preponderate over flowering plants.
The extra-tropical island of New Zealand is preeminently the region of
ferns, many of them arborescent, and of their allies the club-mosses,
which give a luxuriant aspect to the vegetation, where flowering plants
are comparatively rare. Within an area of a few acres, Dr Joseph Hooker
observed thirty-six kinds of ferns, while the same space produced scarcely
twelve flowering plants and trees. Hence, New Zealand is supposed to
possess a climate somewhat resembling that of the carboniferous period,
which is believed to have been humid, mild, and equable.
The lowly ferns of this
country, whose graceful fronds adorn our hillsides and valleys, and fringe
the shady banks of burn and rivulet with their luxuriant verdure, are
characterised by having a creeping stem, or rhizome, running along or
under the surface of the ground. The stem of the tree-fern of other lands
rises into the air, in the form of a slender but stately trunk, surmounted
by a crown of elegant drooping fronds, and resembles a palm in its
appearance and habit of growth. When fully formed, the trunk is hollow,
and is marked on the outside with the scars or cicatrices left by the
falling fronds, which, along with the peculiar appearance of the cellular
tissue and vascular bundles of the interior, enable the botanist to
identify their fossilised remains in the rocks. The stem is formed by the
union of the bases of the leaves, which carry up with them the growing
point; and as the fern-stem, whether horizontal or vertical, increases
only by additions to the summit, this family of plants is called acrogens,
or summit-growers. In the young state, the fronds are rolled up in a
crosier-like manner, familiar to all who have observed the development of
ferns in spring and early summer; and the fronds of tree-ferns, in their
native haunts and in our conservatories, exhibit the same curious
arrangement. The so-called circinate or spiral mode in which the frond is
coiled up, affords an instructive example of provident care in preserving
the tender parts of the young plant from the danger they would incur by
sudden exposure to the atmosphere. Each leaflet is rolled up towards the
rib supporting it,—the rib again toward the midrib,—and the midrib toward
the footstalk. In many species, the crosier-like coil is closely invested
with brownish scales, serving still further to protect the delicate frond
from the chills of early spring, as well as to bar the access of moisture
and the invasion of insects. The whole arrangement presents a beautiful
instance of the "packing" of plants, during the stage of venation, or when
the tender leaf is in the bud; and may readily be studied by any one who
will pick up a fern frond, while it is leisurely unfolding its green
leaflets to the genial airs of spring.
In the tropical zone of
vegetation, tree-ferns grow at an elevation of two or three thousand feet
above the level of the sea, and in favourable circumstances their trunks
attain a height of forty or fifty feet. They can only be imported into
this country in their young state, and then not without difficulty; but
even in their most developed form, they exhibit, on a diminished scale, in
the conservatory, the majesty and grace of their structure and habits in
the warm and humid climate of tropical regions, and even the more
temperate parts of the southern hemisphere, where they give a marked
character to the physiognomy of vegetation. Humboldt describes the
arborescent ferns growing in the shaded clefts on the slopes of the
Cordilleras, as standing out in bold relief against the azure of the sky,
with their thick cylindrical trunks, and delicate lace-like foliage, and
where they are associated with the cinchona tree, yielding the Peruvian
bark. The Cyathea arborea, known in our collections, is a native of the
West Indies, where it grows to a height of twenty-five feet. St Helena
produces the Dicksonia arborescens, which has been observed nowhere else
in the world. One of the most magnificent is Alsophylla excelsa, a native
of Norfolk Island, where it attains to a height of fifty to eighty feet,
with a trunk scarcely a foot in diameter, and a coronet of long pensile
fronds. Speaking of tree-ferns in Australia, twenty feet high, Captain
Mundy remarks:—"When I left England, some of my friends were fern-mad, and
were nursing microscopic varieties with vast anxiety. Would that I could
place them for a minute beneath the patulous umbrella of this magnificent
species of cryptogamia." One familiar arborescent species (Aspidium
baromez), the barometz, or baranetz, called also the Scythian lamb,
possesses a woolly rhizome; and when the fronds are cut off, leaving a
small portion of the stalk, and the specimen is turned upside down,
credulous people have been persuaded, by its appearance, that in the
deserts of Scythia there existed creatures half-animal, half-plant. Sir
Hans Sloane, who founded the British Museum, described and figured it, in
the Philosophical Transactions, under the name of the Tartarian Lamb.
Darwin introduces this fantastic fiction into the "Loves of the Plants:"—
"Cradled in snow, and fann'd
by arctic air,
Shines, gentle Barometz! thy golden hair;
Rooted in earth, each cloven hoof descends,
And round and round her flexile neck she bends;
Crops the gray coral moss and hoary thyme,
Or laps with rosy tongue the melting rime;
Eyes with mute tenderness her distant dam,
Or seems to bleat, a Vegetable Lamb." |
