conditions of air, climate, and rainfall are practically identical. But
soil differs greatly from place to place. Here it's black; there it's
yellow; here it's rich loam; there it's boggy mould or sandy gravel.
And some soils are better adapted to growing certain plants than
others. Rich lowlands and oolites suit the cereals; red marl produces
wonderful grazing grass; bare uplands are best for gorse and heather.
Hence everything favours for the practical man the mistaken idea that
plants and trees grow mainly out of the soil. His own eyes tell him so;
he sees them growing, he sees the visible result undeniable before his
face; while the real act of feeding off the carbon in the air is wholly
unknown to him, being realizable only by the aid of the microscope,
aided by the most delicate and difficult chemical analysis.
Nevertheless French chemists have amply proved by actual experiment
that plants can grow and produce excellent results without any aid from
the soil at all. You have only to suspend the seeds freely in the air
by a string, and supply the rootlets of the sprouting seedlings with a
little water, containing in solution small quantities of manure-stuffs,
and the plants will grow as well as on their native heath, or even
better. Indeed, nature has tried the same experiment on a larger scale
in many cases, as with the cliff-side plants that root themselves in
the naked clefts of granite rocks; the tropical orchids that fasten
lightly on the bark of huge forest trees; and the mosses that spread
even over the bare face of hard brick walls, with scarcely a chink or
cranny in which to fasten their minute rootlets. The insect-eating
plants are also interesting examples in their way of the curious means
which nature takes for keeping up the manure supply under trying
circumstances. These uncanny things are all denizens of loose, peaty
soil, where they can root themselves sufficiently for purposes of
foothold and drink, but where the water rapidly washes away all animal
matter. Under such conditions the cunning sundews and the ruthless
pitcher-plants set deceptive honey traps for unsuspecting insects,
which they catch and kill, absorbing and using up the protoplasmic
contents of their bodies, by way of manure, to supply their quota of
nitrogenous material.
It is the literal fact, then, that plants really eat and live off
carbon, just as truly as sheep eat grass or lions eat antelopes; and
that the green leaves are the mouths and stomachs with which they eat
and digest it. From this it naturally results that the growth and
spread of the leaves must largely depend upon the supply of carbon, as
the growth and fatness of sheep depends upon the supply of pasturage.
Under most circumstances, to be sure, there is carbon enough and to
spare lying about loose for every one of them; but conditions do now
and again occur where we can clearly see the importance of the carbon
supply. Water, for example, contains practically much less carbonic
acid than atmospheric air, especially when the water is stagnant, and
therefore not supplied fresh to the plant from moment to moment. As a
consequence, almost all water-plants have submerged leaves very narrow
and waving, while floating plants, like the water-lilies, have them
large and round, owing to the absence of competition from other kinds
about, which enables them to spread freely in every direction from the
central stalk. Moreover, these leaves, lolling on the water as they do,
have their mouths on the upper instead of the under surface. But the
most remarkable fact of all is that many water plants have two entirely
different types of leaves, one submerged and hair-like, the other
floating and broad or circular. Our own English water-crowfoot, for
example, has the leaves that spring from its stem, below the surface,
divided into endless long waving filaments, which look about in the
water for the stray particles of carbon; but the moment it reaches the
top of its native pond the foliage expands at once into broad lily-like
lobes, that recline on the water like oriental beauties, and absorb
carbon from the air to their heart's content, The one type may be
likened to gills, that similarly catch the dissolved oxygen diffused in
water; the other type may be likened to lungs, that drink in the free
and open air of heaven.
Equally important to the plant, however, with the supply of carbonic
acid, is the supply of sunshine by whose aid to digest it. The carbon
alone is no good to the tree if it can't get something which will
separate it from the oxygen, locked in close embrace with it. That
thing is sunshine. There is nothing, therefore, for which herbs, trees,
and shrubs compete more eagerly than for their fair share of solar
energy. In their anxiety for this they jostle one another down most
mercilessly, in the native condition, grasses struggling up with their
hollow stems above the prone low herbs, shrubs overtopping the grasses
in turn, and trees once more killing out the overshadowed undershrubs.
One must remember that wherever nature has free play, instead of being
controlled by the hand of man, dense forest covers every acre of ground
where the soil is deep enough; gorse, whins, and heather, or their
equivalents grow wherever the forest fails; and herbs can only hold
their own in the rare intervals where these domineering lords of the
vegetable creation can find no foothold. Meadows or prairies occur
nowhere in nature, except in places where the liability to destructive
fires over wide areas together crushes out forest trees, or else where
goats, bison, deer, and other large herbivores browse them ceaselessly
down in the stage of seedlings. Competition for sunlight is thus even
keener perhaps than competition for foodstuffs. Alike on trees, shrubs,
and herbs, accordingly the arrangement of the leaves is always exactly
calculated so as to allow the largest possible horizontal surface, and
the greatest exposure of the blade to the open sunshine. In trees this
arrangement can often be very well observed, all the leaves being
placed at the extremities of the branches, and forming a great
dome-shaped or umbrella-shaped mass, every part of which stands an even
chance of catching its fair share of carbonic acid and solar energy.
The shapes of the leaves themselves are also largely due to the same
cause, every leaf being so designed in form and outline as to interfere
as little as possible with the other leaves on the same stem, as
regards supply both of light and of carbonaceous foodstuffs. It is only
in rare cases, like that of the water-lily, that perfectly round leaves
occur, because the conditions are seldom equal all round, and the
incidence of light and the supply of carbon are seldom unlimited. But
wherever leaves rise free and solitary into the air, without mutual
interference, they are always circular, as may be well seen in the
common nasturtium and the English pennywort. On the other hand, among
dense hedgerows and thickets, where the silent, invisible struggle for
life is fierce indeed, and where sunlight and carbonic acid are
intercepted by a thousand competing mouths and arms, the prevailing
types of leaf are extremely cut up and minutely subdivided into small
lace-like fragments. The plant in such cases can't afford material to
fill up the interstices between the veins and ribs which determine its
underlying architectural structure. Often indeed species which grow
under these hard conditions produce leaves which are, as it were, but
skeleton representatives of their large and well filled-out compeers in
the open meadows.
It is only by bearing vividly in mind this ceaseless and noiseless
struggle between plants for their gaseous food and the sunshine which
enables them to digest it that we can ever fully understand the varying
forms and habits of the vegetable kingdom. To most people, no doubt, it
sounds like pure metaphor to talk of an internecine struggle between
rooted beings which cannot budge one inch from their places, nor fight
with horns, hoofs, or teeth, nor devour one another bodily, nor tread
one another down with ruthless footsteps. But that is only because we
habitually forget that competition is just as really a struggle for
life as open warfare. The men who try against one another for a
clerkship in the City, or a post in a gang of builder's workmen, are
just as surely taking away bread and butter out of their fellows'
mouths for their own advantage, as if they fought for it openly with
fists or six-shooters. The white man who encloses the hunting grounds
of the Indian, and plants them with corn, is just as surely dooming
that Indian to death as if he scalped or tomahawked him. And so too
with the unconscious warfare of plants. The daisy or the plantain that
spreads its rosette of leaves flat against the ground is just as truly
monopolizing a definite space of land as the noble owner of a Highland
deer forest. No blade of grass can spring beneath the shadow of those
tightly pressed little mats of foliage; no fragment of carbon, no ray
of sunshine can ever penetrate below that close fence of living
greenstuff.
Plants, in fact, compete with one another all round for everything they
stand in need of. They compete for their food--carbonic acid. They
compete for their energy--their fair share of sunlight. They compete
for water, and their foothold in the soil. They compete for the favours
of the insects that fertilize their flowers. They compete for the good
services of the birds or mammals that disseminate their seeds in proper
spots for germination. And how real this competition is we can see in a
moment, if we think of the difficulties of human cultivation. There,
weeds are always battling manfully with our crops or our flowers for
mastery over the field or garden. We are obliged to root up with
ceaseless toil these intrusive competitors, if we wish to enjoy the
kindly fruits of the earth in due season. When we leave a garden to
itself for a few short years, we realize at once what effect the
competition of hardy natives has upon our carefully tended and unstable
exotics. In a very brief time the dahlias and phloxes and lilies have
all disappeared, and in their place the coarse-growing docks and
nettles and thistles have raised their heads aloft to monopolize air
and space and sunshine.
Exactly the same struggle is always taking place in the fields and
woods and moors around us, and especially in the spots made over to
pure nature. There, the greenwood tree raises its huge umbrella of
foliage to the skies, and allows hardly a ray of sunlight to struggle
through to the low woodland vegetation of orchid or wintergreen
underneath. Where the soil is not deep enough for trees to root
securely, bushes and heathers overgrow the ground, and compete with
their bell-shaped blossoms for the coveted favour of bees and
butterflies. And in open glades, where for some reason or other the
forest fails, tall grasses and other aspiring herbs run up apace
towards the free air of heaven. Elsewhere, creepers struggle up to the
sun over the stems and branches of stronger bushes or trees, which they
often choke and starve by monopolizing at last all the available carbon
and sunlight. And so throughout; the struggle for life goes on just as
ceaselessly and truly among these unconscious combatants as among the
lions and tigers of the tropical jungle, or among the human serfs of
the overstocked market.
An ounce of example, they say, is worth a pound of precept. So a single
concrete case of a fierce vegetable campaign now actually in progress
over all Northern Europe may help to make my meaning a trifle clearer.
Till very lately the forests of the north were largely composed in
places of the light and airy silver birches. But with the gradual
amelioration of the climate of our continent, which has been going on
for several centuries, the beech, a more southern type of tree, has
begun to spread slowly though surely northward. Now, beeches are greedy
trees, of very dense and compact foliage; nothing else can grow beneath
their thick shade, where once they have gained a foothold; and the
seedlings of the silver birch stand no chance at all in the struggle
for life against the serried leaves of their formidable rivals. The
beech literally eats them out of house and home; and the consequence is
that the thick and ruthless southern tree is at this very moment
gradually superseding over vast tracts of country its more graceful and
beautiful, but far less voracious competitor.
FISH AS FATHERS.
Comparatively little is known as yet, even in this age of publicity,
about the domestic arrangements and private life of fishes. Not that
the creatures themselves shun the wiles of the interviewer, or are at
all shy and retiring, as a matter of delicacy, about their family
affairs; on the contrary, they display a striking lack of reticence in
their native element, and are so far from pushing parental affection to
a quixotic extreme that many of them, like the common rabbit
immortalised by Mr. Squeers, 'frequently devour their own offspring.'
But nature herself opposes certain obvious obstacles to the pursuit of
knowledge in the great deep, which render it difficult for the ardent
naturalist, however much he may be so disposed, to carry on his
observations with the same facility as in the case of birds and
quadrupeds. You can't drop in upon most fish, casually, in their own
homes; and when you confine them in aquariums, where your opportunities
of watching them through a sheet of plate-glass are considerably
greater, most of the captives get huffy under the narrow restrictions
of their prison life, and obstinately refuse to rear a brood of
hereditary helots for the mere gratification of your scientific
curiosity.
Still, by hook and by crook (especially the former), by observation
here and experiment there, naturalists in the end have managed to piece
together a considerable mass of curious and interesting information of
an out-of-the-way sort about the domestic habits and manners of sundry
piscine races. And, indeed, the morals of fish are far more varied and
divergent than the uniform nature of the world they inhabit might lead
an _à priori_ philosopher to imagine. To the eye of the mere casual
observer every fish would seem at first sight to be a mere fish, and to
differ but little in sentiments and ethical culture from all the rest
of his remote cousins. But when one comes to look closer at their
character and antecedents, it becomes evident at once that there is a
deal of unsuspected originality and caprice about sharks and flat-fish.
Instead of conforming throughout to a single plan, as the young, the
gay, the giddy, and the thoughtless are too prone to conclude, fish are
in reality as various and variable in their mode of life as any other
great group in the animal kingdom. Monogamy and polygamy, socialism and
individualism, the patriarchal and matriarchal types of government, the
oviparous and viviparous methods of reproduction, perhaps even the
dissidence of dissent and esoteric Buddhism, all alike are well
represented in one family or another of this extremely eclectic and
philosophically unprejudiced class of animals.
If you want a perfect model of domestic virtue, for example, where can
you find it in higher perfection than in that exemplary and devoted
father, the common great pipe-fish of the North Atlantic and the
British Seas? This high-principled lophobranch is so careful of its
callow and helpless young that it carries about the unhatched eggs with
him under his own tail, in what scientific ichthyologists pleasantly
describe as a subcaudal pouch or cutaneous receptacle. There they hatch
out in perfect security, free from the dangers that beset the spawn and
fry of so many other less tender-hearted kinds; and as soon as the
little pipe-fish are big enough to look after themselves the sac
divides spontaneously down the middle, and allows them to escape, to
shift for themselves in the broad Atlantic. Even so, however, the
juniors take care always to keep tolerably near that friendly shelter,
and creep back into it again on any threat of danger, exactly as
baby-kangaroos do into their mother's marsupium. The father-fish, in
fact, has gone to the trouble and expense of developing out of his own
tissues a membranous bag, on purpose to hold the eggs and young during
the first stages of their embryonic evolution. This bag is formed by
two folds of the skin, one of which grows out from each side of the
body, the free margins being firmly glued together in the middle by a
natural exudation, while the eggs are undergoing incubation, but
opening once more in the middle to let the little fish out as soon as
the process of hatching is fairly finished.
So curious a provision for the safety of the young in the pipe-fish may
be compared to some extent, as I hinted above, with the pouch in which
kangaroos and other marsupial animals carry their cubs after birth,
till they have attained an age of complete independence. But the
strangest part of it all is the fact that while in the kangaroo it is
the mother who owns the pouch and takes care of the young, in the
pipe-fish it is the father, on the contrary, who thus specially
provides for the safety of his defenceless offspring. And what is odder
still, this topsy-turvy arrangement (as it seems to us) is the common
rule throughout the class of fishes. For the most part it must be
candidly admitted by their warmest admirer, fish make very bad parents
indeed. They lay their eggs anywhere on a suitable spot, and as soon as
they have once deposited them, like the ostrich in Job, they go on
their way rejoicing, and never bestow another passing thought upon
their deserted progeny. But if ever a fish _does_ take any pains in the
education and social upbringing of its young, you're pretty sure to
find on enquiry it's the father--not as one would naturally expect, the
mother--who devotes his time and attention to the congenial task of
hatching or feeding them. It is he who builds the nest, and sits upon
the eggs, and nurses the young, and imparts moral instruction (with a
snap of his jaw or a swish of his tail) to the bold, the truant, the
cheeky, or the imprudent; while his unnatural spouse, well satisfied
with her own part in having merely brought the helpless eggs into this
world of sorrow, goes off on her own account in the giddy whirl of
society, forgetful of the sacred claims of her wriggling offspring upon
a mother's heart.
In the pipe-fish family, too, the ardent evolutionist can trace a whole
series of instructive and illustrative gradations in the development of
this instinct and the corresponding pouch-like structure among the male
fish. With the least highly-evolved types, like the long-nosed
pipe-fish of the English Channel, and many allied forms from European
seas, there is no pouch at all, but the father of the family carries
the eggs about with him, glued firmly on to the service of his abdomen
by a natural mucus. In a somewhat more advanced tropical kind, the
ridges of the abdomen are slightly dilated, so as to form an open
groove, which loosely holds the eggs, though its edges do not meet in
the middle as in the great pipe-fish. Then come yet other more
progressive forms, like the great pipe-fish himself, where the folds
meet so as to produce a complete sac, which opens at maturity, to let
out its little inmates. And finally, in the common Mediterranean
sea-horses, which you can pick up by dozens on the Lido at Venice, and
a specimen of which exists in the dried form in every domestic museum,
the pouch is permanently closed by coalescence of the edges, leaving a
narrow opening in front, through which the small hippocampi creep out
one by one as soon as they consider themselves capable of buffeting the
waves of the Adriatic.
Fish that take much care of their offspring naturally don't need to
produce eggs in the same reckless abundance as those dissipated kinds
that leave their spawn exposed on the bare sandy bottom, at the mercy
of every comer who chooses to take a bite at it. They can afford to lay
a smaller number, and to make each individual egg much larger and
richer in proportion than their rivals. This plan, of course, enables
the young to begin life far better provided with muscles and fins than
the tiny little fry which come out of the eggs of the improvident
species. For example, the cod-fish lays nine million odd eggs; but
anybody who has ever eaten fried cod's-roe must needs have noticed that
each individual ovum was so very small as to be almost indistinguishable
to the naked eye. Thousands of these infinitesimal specks are devoured
before they hatch out by predaceous fish; thousands more of the young
fry are swallowed alive during their helpless infancy by the enemies of
their species. Imagine the very fractional amount of parental affection
which each of the nine million must needs put up with! On the other
hand, there is a paternally-minded group of cat-fish known as the genus
_Arius_, of Ceylon, Australia, and other tropical parts, the males of
which carry about the ova loose in their mouths, or rather in an
enlargement of the pharynx, somewhat resembling the pelican's pouch;
and the spouses of these very devoted sires lay accordingly only very
few ova, all told, but each almost as big as a hedge-sparrow's egg--a
wonderful contrast to the tiny mites of the cod-fish. To put it
briefly, the greater the amount of protection afforded the eggs, the
smaller the number and the larger the size. And conversely, the larger
the size of the egg to start with, the better fitted to begin the
battle of life is the young fish when first turned out on a cold world
upon his own resources.
This is a general law, indeed, that runs through all nature, from
London slums to the deep sea. Wasteful species produce many young, and
take but little care of them when once produced. Economical species
produce very few young, but start each individual well-equipped for its
place in life and look after them closely till they can take care of
themselves in the struggle for existence. And on the average, however
many or however few the offspring to start with, just enough attain
maturity in the long run to replace their parents in the next
generation. Were it otherwise, the sea would soon become one solid mass
of herring, cod, and mackerel.
These cat-fish, however, are not the only good fathers that carry their
young (like woodcock) in their own mouths. A freshwater species of the
Sea of Galilee, _Chromis Andreæ_ by name (dedicated by science to the
memory of that fisherman apostle, St. Andrew, who must often have
netted them), has the same habit of hatching out its young in its own
gullet: and here again it is the male fish upon whom this apparently
maternal duty devolves, just as it is the male cassowary that sits upon
the eggs of his unnatural mate, and the male emu that tends the nest,
while the hen bird looks on superciliously and contents herself with
exercising a general friendly supervision of the nursery department. I
may add parenthetically that in most fish families the eggs are
fertilised after they have been laid, instead of before, which no doubt
accounts for the seeming anomaly.