it by the simple device of wings or feathery projections. Every variety
of plan or dodge or expedient has been adopted in turn to secure the
self-same end; and provided only it succeeds in securing it, any
variety of them all is equally satisfactory. One might parallel it with
the case of hatching birds' eggs. Most birds sit upon their eggs
themselves, and supply the necessary warmth from their own bodies. But
any alternative plan that attains the same end does just as well. The
felonious cuckoo drops her foundlings unawares in another bird's nest:
the ostrich trusts her unhatched offspring to the heat of the burning
desert sand: and the Australian brush-turkeys, with vicarious maternal
instinct, collect great mounds of decaying and fermenting leaves and
rubbish, in which they deposit their eggs to be artificially incubated,
as it were, by the slow heat generated in the process of putrefaction.
Just in the same way, we shall see in the case of seeds that any method
of dispersion will serve the plant's purpose equally well, provided
only it succeeds in carrying a few of the young seedlings to a proper
place in which they may start fair at last in the struggle for
existence.
As in the case of the fertilization of flowers, so in that of the
dispersal of seeds, there are two main ways in which the work is
effected--by animals and by wind-power. I will not insult the
intelligence of the reader at the present time of day by telling him
that pollen is usually transferred from blossom to blossom in one or
other of these two chief ways--it is carried on the heads or bodies of
bees and other honey-seeking insects, or else it is wafted on the wings
of the wind to the sensitive surface of a sister-flower. So, too, seeds
are for the most part either dispersed by animals or blown about by the
breezes of heaven to new situations. These are the two most obvious
means of locomotion provided by nature; and it is curious to see that
they have both been utilized almost equally by plants, alike for their
pollen and their seeds, just as they have been utilized by man for his
own purposes on sea or land, in ship, or windmill, or pack-horse, or
carriage.
There are two ways in which animals may be employed to disperse
seeds--voluntarily and involuntarily. They may be compelled to carry
them against their wills: or they may be bribed and cajoled and
flattered into doing the plant's work for it in return for some
substantial advantage or benefit the plant confers upon them. The first
plan is the one adopted by burrs and cleavers. These adhesive fruits
are like the man who buttonholes you and won't be shaken off: they are
provided with little curved hooks or bent and barbed hairs which catch
upon the wool of sheep, the coat of cattle, or the nether integuments
of wayfaring humanity, and can't be got rid of without some little
difficulty. Most of them, you will find on examination, belonged to
confirmed hedgerow or woodside plants: they grow among bushes or low
scrub, and thickets of gorse or bramble. Now, to such plants as these,
it is obviously useful to have adhesive fruits and seeds: for when
sheep or other animals get them caught in their coats, they carry them
away to other bushy spots, and there, to get rid of the annoyance
caused by the foreign body, scratch them off at once against some
holly-bush or blackthorn. You may often find seeds of this type
sticking on thorns as the nucleus of a little matted mass of wool, so
left by the sheep in the very spots best adapted for the free growth of
their vigorous seedlings.
Even among plants which trust to the involuntary services of animals in
dispersing their seeds, a great many varieties of detail may be
observed on close inspection. For example, in hound's-tongue and
goose-grass, two of the best-known instances among our common English
weeds, each little nut is covered with many small hooks, which make it
catch on firmly by several points of attachment to passing animals.
These are the kinds we human beings of either sex oftenest find
clinging to our skirts or trousers after a walk in a rabbit-warren. But
in herb-bennet and avens each nut has a single long awn, crooked near
the middle with a very peculiar S-shaped joint, which effectually
catches on to the wool or hair, but drops at the elbow after a short
period of withering. Sometimes, too, the whole fruit is provided with
prehensile hooks, while sometimes it is rather the individual seeds
themselves that are so accommodated. Oddest of all is the plan followed
by the common burdock. Here, an involucre or common cup-shaped
receptacle of hooked bracts surrounds an entire head of purple tubular
flowers, and each of these flowers produces in time a distinct fruit;
but the hooked involucre contains the whole compound mass, and, being
pulled off bodily by a stray sheep or dog, effects the transference of
the composite lot at once to some fitting place for their germination.
Those plants, on the other hand, which depend rather, like London
hospitals, upon the voluntary system, produce that very familiar form
of edible capsule which we commonly call in the restricted sense a
fruit or berry. In such cases, the seed-vessel is usually swollen and
pulpy: it is stored with sweet juices to attract the birds or other
animal allies, and it is brightly coloured so as to advertise to their
eyes the presence of the alluring sugary foodstuff. These instances,
however, are now so familiar to everybody that I won't dwell upon them
at any length. Even the degenerate schoolboy of the present day, much
as he has declined from the high standard set forth by Macaulay, knows
all about the way the actual seed itself is covered (as in the plum or
the cherry) by a hard stony coat which 'resists the action of the
gastric juice' (so physiologists put it, with their usual frankness),
and thus passes undigested through the body of its swallower. All I
will do here, therefore, is to note very briefly that some edible
fruits, like the two just mentioned, as well as the apricot, the peach,
the nectarine, and the mango, consist of a single seed with its outer
covering; in others, as in the raspberry, the blackberry, the
cloudberry, and the dew-berry, many seeds are massed together, each
with a separate edible pulp; in yet others, as in the gooseberry, the
currant, the grape, and the whortleberry, several seeds are embedded
within the fruit in a common pulpy mass; and in others again, as in the
apple, pear, quince, and medlar, they are surrounded by a quantity of
spongy edible flesh. Indeed, the variety that prevails among fruits in
this respect almost defies classification: for sometimes, as in the
mulberry, the separate little fruits of several distinct flowers grow
together at last into a common berry: sometimes, as in a fig, the
general flower-stalk of several tiny one-seeded blossoms forms the
edible part: and sometimes, as in the strawberry, the true little nuts
or fruits appear as mere specks or dots on the bloated surface of the
swollen and overgrown stem, which forms the luscious morsel dear to the
human palate.
Yet in every case it is interesting to observe that, while the seeds
which depend for dispersion upon the breeze are easily detached from
the parent plant and blown about by every wind of doctrine, the seeds
or fruits which depend for their dispersion upon birds or animals
always, on the contrary, hang on to their native boughs to the very
last, till some unconscious friend pecks them off and devours them.
Haws, rose-hips, and holly-berries will wither and wilt on the tree in
mild winters, because they can't drop off of themselves without the aid
of birds, while the birds are too well supplied with other food to care
for them. One of the strangest cases of all, however, is that of the
mistletoe, which, living parasitically upon the forest-boughs and
apple-trees, would of course be utterly lost if its berries dropped
their seeds on to the ground beneath it. To avoid such a misfortune,
the mistletoe berries are filled with an exceedingly viscid and sticky
pulp, surrounding the hard little nut-like seeds: and this pulp makes
the seeds cling to the bills and feet of various birds which feed upon
the fruit, but most particularly of the missel thrush, who derives his
common English name from his devotion to the mistletoe. The birds then
carry them away unwittingly to some neighbouring tree, and rub them
off, when they get uncomfortable, against a forked branch--the exact
spots that best suits the young mistletoe for sprouting in. Man, in
turn, makes use of the sticky pulp for the manufacture of bird-lime,
and so employs against the birds the very qualities which the plant
intended as a bribe for their kindly services.
Among seeds that trust for their disposal to the wind, the commonest,
simplest, and least evolved type is that of the ordinary capsule, as in
the poppies and campions. At first sight, to be sure, a casual observer
might suppose there existed in these cases no recognisable device at
all for the dissemination of the seedlings. But you and I, most
excellent and discreet reader, are emphatically _not_, of course, mere
casual observers. _We_ look close, and go to the very root of things.
And when we do so, we see for ourselves at once that almost all
capsules open--where? why, at the top, so that the seeds can only be
shaken out when there is a high enough wind blowing to sway the stems
to and fro with some violence, and scatter the small black grains
inside to a considerable distance. Furthermore, in many instances, of
which the common poppy-head is an excellent example, the capsule opens
by lateral pores at the top of a flat head--a further precaution which
allows the seeds to get out only by a few at a time, after a distinct
jerk, and so scatters them pretty evenly, with different winds, over a
wide circular space around the mother plant. Experiment will show how
this simple dodge works. Try to shake out the poppy-seed from a ripe
poppy-head on the plant as it grows, without breaking the stem or
bending it unnaturally, and you will easily see how much force of wind
is required in order to put this unobtrusive but very effective
mechanism into working order.
The devices of this character employed by various plants for the
dispersal of seeds even in ordinary dry capsules are far too numerous
for me to describe in full detail, though they form a delightful
subject for individual study in any small suburban garden. I will only
give one more illustrative case, just to show the sort of point an
amateur should always be on the look-out for. There is an extremely
common, though inconspicuous, English weed, the mouse-ear chickweed,
found everywhere in flower-beds or grass-plots, however small, and
noticeable for its quaint little horn-shaped capsules. These have a
very odd sort of twist or cock-up in the middle, just above the part
where the seeds lie; and they open at the top by ten small teeth,
pointed obliquely outward for no apparent reason. Yet every point has a
meaning of its own for all that. The plant is one that lies rather
close upon the ground; and the effect of this twist in the capsule is
that the seeds, which are relatively heavy, and well stored with
nutriment, can never get out at all, unless a very strong wind is
blowing, which sweeps over the herbage in long quick waves, and carries
everything it shakes out for great distances before it. So much design
have even the smallest weeds put into the mechanism for the dispersion
of their precious seeds, the hope of their race and the earnest of
their future!
Artillery marks a higher stage than the sling and the stone. Just so,
in many plants, a step higher in the evolutionary scale as regards the
method of dispersion, the capsule itself bursts open explosively, and
scatters its contents to the four winds of heaven. Such plants may be
said to discharge their grains on the principle of the bow and arrow.
The balsam is a familiar example of this startling mode of moving to
fresh fields and pastures new: its capsule consists of five long
straight valves, which break asunder elastically the moment they are
touched, when fully ripe, and shed their seeds on all sides, like so
many small bombshells. Our friend the squirting cucumber, which served
as the prime text for this present discourse, falls into somewhat the
same category, though in other ways it rather resembles the true
succulent fruits, and belongs, indeed, to the same family as the melon,
the gourd, the pumpkin, and the vegetable-marrow, almost all of which
are edible and in every way fruit-like. Among English weeds, the little
bittercress that grows on dry walls and hedge-banks forms an excellent
example of the same device. Village children love to touch the long,
ripe, brown capsules on the top with one timid finger, and then jump
away, half laughing, half terrified, when the mild-looking little plant
goes off suddenly with a small bang and shoots its grains like a
catapult point-blank in their faces.
It is in the tropics, however, that these elastic fruits reach their
highest development. There they have to fight, not merely against such
small fry as robins, squirrels, and harvest-mice, but against the
aggressive parrot, the hard-billed toucan, the persistent lemur, and
the inquisitive monkey. Moreover, the elastic fruits of the tropics
grow often on spreading forest trees, and must therefore shed their
seeds to immense distances if they are to reach comparatively virgin
soil, unexhausted by the deep-set roots of the mother trunk. Under such
exceptional circumstances, the tropical examples of these elastic
capsules are by no means mere toys to be lightly played with by babes
and sucklings. The sand-box tree of the West Indies has large round
fruits, containing seeds about as big as an English horsebean; and the
capsule explodes, when ripe, with a detonation like a pistol,
scattering its contents with as much violence as a shot from an
air-gun. It is dangerous to go too near these natural batteries during
the shooting season. A blow in the eye from one would blind a man
instantly. I well remember the very first night I spent in my own house
in Jamaica, where I went to live shortly after the repression of
'Governor Eyre's rebellion,' as everybody calls it locally. All night
long I heard somebody, as I thought, practising with a revolver in my
own back garden: a sound which somewhat alarmed me under those very
unstable social conditions. An earthquake about midnight, it is true,
diverted my attention temporarily from the recurring shots, but didn't
produce the slightest effect upon the supposed rebel's devotion to the
improvement of his marksmanship. When morning dawned, however, I found
it was only a sand-box tree, and that the shots were nothing more than
the explosions of the capsules. As to the wonderful tales told about
the Brazilian cannon-ball tree, I cannot personally endorse them from
original observation, and will not stain this veracious page with any
second-hand quotations from the strange stories of modern scientific
Munchausens.
Still higher in the evolutionary scale than the elastic fruits are
those airy species which have taken to themselves wings like the eagle,
and soar forth upon the free breeze in search of what the Americans
describe as 'fresh locations.' Of this class the simplest type may be
seen in those forest-trees, like the maple and the sycamore, whose
fruits are flattened out into long expansions or parachutes,
technically known as 'keys,' by whose aid they flutter down obliquely
to the ground at a considerable distance. The keys of the sycamore, to
take a single instance, when detached from the tree in autumn, fall
spirally through the air owing to the twist of the winged arm, and are
carried so far that, as every gardener knows, young sycamore trees rank
among the commonest weeds among our plots and flower-beds. A curious
variant upon this type is presented by the lime, or linden, whose
fruits are in themselves small wingless nuts; but they are born in
clusters upon a common stalk, which is winged on either side by a large
membranous bract. When the nuts are ripe, the whole cluster detaches
itself in a body from the branch, and flutters away before the breeze
by means of the common parachute, to some spot a hundred yards or more,
where the wind chances to land it.
The topmost place of all in the hierarchy of seed life, it seems to me,
is taken by the feathery fruits and seeds which float freely hither and
thither wherever the wind may bear them. An immense number of the very
highest plants--the aristocrats of the vegetable kingdom, such as the
lordly composites, those ultimate products of plant evolution--possess
such floating feathery seeds; though here, again, the varieties of
detail are too infinite for rapid or popular classification. Indeed,
among the composites alone--the thistle and dandelion tribe with downy
fruits--I can reckon up more than a hundred and fifty distinct
variations of plan among the winged seeds known to me in various parts
of Europe. But if I am strong, I am merciful: I will let the public off
with a hundred and forty-eight of them. My two exceptions shall be
John-go-to-bed-at-noon and the hairy hawkweed, both of them common
English meadow-plants. The first, and more quaintly named, of the two
has little ribbed fruits that end in a long and narrow beak, supporting
a radial rib-work of spokes like the frame of an umbrella; and from rib
to rib of this framework stretch feathery cross-pieces, continuous all
round, so as to make of the whole mechanism a perfect circular
parachute, resembling somewhat the web of a geometrical spider. But the
hairy hawkweed is still more cunning in its generation; for that clever
and cautious weed produces its seeds or fruits in clustered heads, of
which the central ones are winged, while the outer are heavy, squat,
and wingless. Thus does the plant make the best of all chances that may
happen to open before it: if one lot goes far and fares but ill, the
other is pretty sure to score a bull's-eye.
These are only a few selected examples of the infinite dodges employed
by enlightened herbs and shrubs to propagate their scions in foreign
parts. Many more, equally interesting, must be left undescribed. Only
for a single case more can I still find room--that of the subterranean
clover, which has been driven by its numerous enemies to take refuge at
last in a very remarkable and almost unique mode, of protecting its
offspring. This particular kind of clover affects smooth and
close-cropped hillsides, where the sheep nibble down the grass and
other herbage almost as fast as it springs up again. Now, clover seeds
resemble their allies of the pea and bean tribe in being exceedingly
rich in starch and other valuable foodstuffs. Hence, they are much
sought after by the inquiring sheep, which eat them off wherever found,
as exceptionally nutritious and dainty morsels. Under these
circumstances, the subterranean clover has learnt to produce small
heads of bloom, pressed close to the ground, in which only the outer
flowers are perfect and fertile, while the inner ones are transformed
into tiny wriggling corkscrews. As soon as the fertile flowers have
begun to set their seed, by the kind aid of the bees, the whole stem
bends downward, automatically, of its own accord; the little corkscrews
then worm their way into the turf beneath; and the pods ripen and
mature in the actual soil itself, where no prying ewe can poke an
inquisitive nose to grub them up and devour them. Cases like this point
in certain ways to the absolute high-water-mark of vegetable ingenuity:
they go nearest of all in the plant-world to the similitude of
conscious animal intelligence.
A DESERT FRUIT.
Who knows the Mediterranean, knows the prickly pear. Not that that
quaint and uncanny-looking cactus, with its yellow blossoms and
bristling fruits that seem to grow paradoxically out of the edge of
thick fleshy leaves, is really a native of Italy, Spain, and North
Africa, where it now abounds on every sun-smitten hillside. Like Mr.
Henry James and Mr. Marion Crawford, the Barbary fig, as the French
call it, is, in point of fact, an American citizen, domiciled and half
naturalised on this side of the Atlantic, but redolent still at heart
of its Columbian origin. Nothing is more common, indeed, than to see
classical pictures of the Alma-Tadema school--not, of course, from the
brush of the master himself, who is impeccable in such details, but
fair works of decent imitators--in which Caia or Marcia leans
gracefully in her white stole on one pensive elbow against a marble
lintel, beside a courtyard decorated with a Pompeian basin, and
overgrown with prickly pear or "American aloes." I need hardly say
that, as a matter of plain historical fact, neither cactuses nor agaves
were known in Europe till long after Christopher Columbus had steered
his wandering bark to the sandy shores of Cat's Island in the Bahamas.
(I have seen Cat's Island with these very eyes, and can honestly assure
you that its shores _are_ sandy.) But this is only one among the many
pardonable little inaccuracies of painters, who thrust scarlet
geraniums from the Cape of Good Hope into the fingers of Aspasia, or
supply King Solomon in all his glory with Japanese lilies of the most
recent introduction.
At the present day, it is true, both the prickly-pear cactus and the
American agave (which the world at large insists upon confounding with
the aloe, a member of a totally distinct family) have spread themselves
in an apparently wild condition over all the rocky coasts both of
Southern Europe and of Northern Africa. The alien desert weeds have
fixed their roots firmly in the sunbaked clefts of Ligurian Apennines;
the tall candelabrum of the western agave has reared its great spike of
branching blossoms (which flower, not once in a century, as legend
avers, but once in some fifteen years or so) on all the basking
hillsides of the Mauritanian Atlas. But for the origin, and therefore
for the evolutionary history, of either plant, we must look away from
the shore of the inland sea to the arid expanse of the Mexican desert.
It was there, among the sweltering rocks of the Tierras Calientes, that
these ungainly cactuses first learned to clothe themselves in prickly
mail, to store in their loose tissues an abundant supply of sticky
moisture, and to set at defiance the persistent attacks of all external
enemies. The prickly pear, in fact, is a typical instance of a desert
plant, as the camel is a typical instance of a desert animal. Each lays
itself out to endure the long droughts of its almost rainless habitat
by drinking as much as it can when opportunity offers, hoarding up the
superfluous water for future use, and economising evaporation by every
means in its power.
If you ask that convenient fiction, the Man in the Street, what sort of
plant a cactus is, he will probably tell you it is all leaf and no
stem, and each of the leaves grows out of the last one. Whenever we set
up the Man in the Street, however, you must have noticed we do it in
order to knock him down again like a nine-pin next moment: and this
particular instance is no exception to the rule; for the truth is that
a cactus is practically all stem and no leaves, what looks like a leaf
being really a branch sticking out at an angle. The true leaves, if
there are any, are reduced to mere spines or prickles on the surface,
while the branches, in the prickly-pear and many of the ornamental
hot-house cactuses, are flattened out like a leaf to perform foliar
functions. In most plants, to put it simply, the leaves are the mouths
and stomachs of the organism; their thin and flattened blades are
spread out horizontally in a wide expanse, covered with tiny throats
and lips which suck in carbonic acid from the surrounding air, and
disintegrate it in their own cells under the influence of sunlight. In
the prickly pears, on the contrary, it is the flattened stem and
branches which undertake this essential operation in the life of the
plant--the sucking-in of carbon and giving-out of oxygen, which is to
the vegetable exactly what the eating and digesting of food is to the
animal organism. In their old age, however, the stems of the prickly
pear display their true character by becoming woody in texture and
losing their articulated leaf-like appearance.