For what happens to the carbon that is left behind when the oxygen is expelled? Just as the cells of chlorophyll set to work upon it when it came in, so when it is separated they instantly combine it with the ingredients brought up the ascending sap and awaiting treatment in the ante-chambers. The cavity of that wonderful cell not only decomposes carbon dioxide, it composes new compounds. The carbon is immediately transformed. By combining with other ingredients gathered from the soil it instantly becomes the raw material of sugar, starch, wood, flowers, and fruit. In this state it is known as the Descending Sap. The ascending sap carried up certain properties. Combined with what has been taken from the atmosphere, those properties, forged in the cellular furnace, have gone to make a final substance which flows down the plant distributing largesse as it goes – leaf-tissue for the leaves; colour and scent for the flowers; starch, sugar, and jelly for the fruit; fibres for the wood; cork for the bark; and gossamer for the roots.
Thus the sap’s circle is completed.
By mentioning ‘flowers’ above I have anticipated our story. The buds do not always open into green leaves which set at work those masters in the art of chemistry, the cells of chlorophyll, that weave the wood and build the twigs and feed the whole concern. These work unceasingly for a prosperous present. They care nothing for the future. But the buds also open into other leaves that do not toil and do not spin in that way, and yet are clothed, not in modest green, but in a softer raiment, embellished and perfumed, the admiration of the world. These are flowers. They also work of course – beauty is always incidental – but their work looks to the future.
These flowers are made from the same materials, based on the same architecture, and raised by the same labourers as the other buds. This is the more surprising when we observe how different their instruments are. The following must serve as a general example. Passing our eyes from without inwards we see first a few lovely soft leaves called petals, the total of which is well crowned by the name corolla. Next stand in a circle half a dozen little pillars called stamens, each terminating with a head called the anther, and full of dust called pollen. In the centre is another pillar like a walking stick with a good knob-handle and a sheath at the bottom – this is the pistil, the knob being the stigma, the shaft the style, and the sheath the ovary, which is full of rudimentary seeds called ovules. We should add that the whole flower may be protected by some green tongues called in sum the calyx.
Such is a full flower. Any flower can get on with less than this, with only stamens and pistil if necessary. Thus some plants, lacking the gorgeous paraphernalia of petals, may give the impression that they have no flowers, though all plants have flowers, all plants have fruit, and to talk about flowers as if they appear on some plants and not on others, and to talk of fruit trees as if any tree or shrub could fail to bear fruit, is to suggest that Nature moves with a view to man’s aesthetic tastes and gastronomic desires.
The purpose of the erection is to work for the future – to make seeds. Given the above instruments, how is it done? Briefly, by an exchange between the stamens and the pistil: more accurately, by the pollen reaching the ovules and striking up with them the spark of life – which we call the moment of fertilization. Inside the anthers of the stamens the pollen is found in the shape of countless grains each consisting of a single cell with a double envelope harbouring a viscous liquid in which float numbers of minute granulations called the fovilla – for, as we are constantly finding out, Nature delights in the utterly and increasingly minute no less than in the gigantic.
One thing more we should observe since it bears so much upon the pleasure we get from looking at flowers. At various places in the interior of the corolla there are pockets or pouches of nectar in order to attract insects who shall come and disperse the pollen, should the wind fail to do so. And in order to signify the presence of these tempting morsels the petals serve as painted flags.
When the flower is fully blown and the anthers have let loose the dusty pollen to be scattered by the wind or carried by the insects, then the stigma proceeds to exude a liquid slightly thinner than the liquid held within the grains of pollen, so that when the latter falls upon it, it sticks, and while it sticks there the action of endosmosis is again set going so that the liquid of the stigma passing into the grains of pollen pushes out the fovilla, handsomely packed in a painted tube, which, penetrating the stigma and passing down the style, enters the ovary and reaches the chamber of ovules. And then – how is the vivifying influence brought about, by what means is the flame of life enkindled? At this point all great scientists are silent and give up the chase, declaring – ‘No one knows. Before these mysteries of life reason bows, helpless, and abandons itself to an impulse of adoration to the Author of these ineffable miracles.’
Once the ovules have been given life and have achieved the status of seeds, then the life of the flower is over; the beautiful petals that advertised the pollen, the stamens that pillared it, the pistil that received it, fall to the ground, disregarded now in their withered and scarred disgrace of ruin. But the ovary, at first so thin, swells with increasing pride of colour and shape, until it seems to us as we gaze upon the astounding apple, that the petiole cannot possibly bear such a weight without breaking. Finally the seed is loosened and leaves the parent plant, and is dispersed by a hundred different methods across the land.
8 The Plant: Apostrophe to an Urban Gentleman
It is past five-thirty in the afternoon. For us on the land work is over. We can rest. But when we have gone home, the workshop we have left behind does not close down. We can go home and leave Nature to it, knowing that she will not rest, she will not take off.
Recently I heard a man who was visiting his wife in the country, say – ‘Give me the plant at home any day.’ He was a progressive man with far more use for a piston than a pistil. By the plant he meant the factory, and it was clear that for him factories constituted the only plants worthy of the name.
If Nature were not so silent he might have changed his opinion. There is nothing like noise for suggesting importance. Had we a finer sense of sound we might be able to hear the natural movements. Could he have heard all that was going on around him that man might have been impressed.
Even so, without hearing anything, could such a man contrive to gaze upon the work in progress here with concentrated attention over a period of time, looking down upon it from the Hill of Knowledge, as it were; could he cast his eyes from above the earth to beneath the surface of the soil and attend at the first movement after the seed is sown and see the approach of the water, the cracking of the envelopes, the swelling of the perisperm, the awakening of the embryos from their slumber in the dormitories of the seeds; could he see the translation of the hoarded starch into the magic liquid of glucose from which proceed stems that press up to the light and roots that dig down in the dark; could he see the roots select from the great storehouse of chemical foods flowing within the soil those which they need while rejecting those which they do not, and then under the pressure of endosmosis and by the power of capillarity raise up whole reservoirs of water to the skies; could he see that sap ascend creating as its fluid flows the extra limbs and mouths that soon shall feed the whole; could he see those leaves open out their blades to embrace the sunshine’s beaming blows and seek the air for gases while the roots explore the darkness of the earth for liquids; could he see the stomata on the leaves spraying forth to heaven the tented tons of water which have carried up the chemicals into the antechambers of the epidermis; could he see those same stomata taking in the carbon acid gas so that the leaves may pasture on our poison; could he draw closer and observe the operations carried out by those master miracle workers, the cells of chlorophyll, in the laboratory of the parenchyma where oxygen is separated from carbon and restored to the atmosphere, where carbon is compounded with other elements and turned into other things, where the hard branches reaching up to the loftiest brightness are first boiled together in this burning cauldron of cr
eation; could he see that sap after ascension being thus combined and treated then descending through the ribbed corridors of the nervures on the leaves through the green-paved passages of the petioles, through the fluted pillars and the twisted towers of the stems, down into the roots, distributing good as it goes; could he see these toilers for the present erecting those toilers for the future whose coloured petals and glorious perfumes are the delight of all mankind; could he, still standing on his Hill, still standing there, making use of the divine gift that has been bestowed upon men, the gift to learn, to see, to comprehend something of the Mystery and the Law, could he now turn his gaze upon those flowers in their maturity and see the clouds of pollen borne from the anthers on the wings of the wind or the backs of bees, throw down their fovilla on to the receiving stigmas; could he see the penetration of the pollinic tubes as they pierce the sticky surface of the pistil and then pass down the style into the ovary at the base; could he see this final act, more powerful than that which happens within the perisperm of the grain, more wonderful even than the elaborations in the laboratory of the parenchyma, the final act or the First Act, the moment when the ovule in the ovary becomes a seed, when the spark of a new life is kindled and the Wheel revolves again; could he gaze upon this Plant tirelessly toiling for us and spinning for us, it might happen that he would come to think that it compares not unfavourably with his factory at home.
9 The Imperialism of the Plants
One July day while hoeing in a beanfield which had become badly overrun with thistles, I was surprised to find myself suddenly caught in a blizzard. The flakes whirled about, very thick, not falling from above but rising from below. It was thistle-seed, of course, which had become suddenly airborne in a gust of wind. A very remarkable sight all the same; and it set me thinking of the various ways by which plants disperse themselves throughout the world.
The great aim of any given plant, it would seem, is not only the continuation of the species, but colonization and empire. Few are content with local habitation. They wish to spread themselves across the world. To this end they employ many means of transport. They charter the birds to chariot them across continents and seas. They engage animals and insects to transfer them from place to place. They use floating driftwood and logs and barges on river and lake. They harness the wind and become their own aeroplanes. They surrender to the currents of the ocean and become their own ships. They encourage mankind to administer to their imperial needs. Some even move along the ground unaided.
Let us imagine an island somewhere in the ocean – in the Pacific, say – which has been let down from the sky for our benefit. We will suppose that it had no plants on it. And there we stand, awaiting the arrival of seeds. They will come; for if Nature hates a vacuum, she detests a piece of soil with nothing on it.
Looking out to sea we soon catch sight of a swimmer, making for the beach – evidently a shipwrecked native. His brown head is clearly seen. But when it reaches shore we find that this brown head is really a coconut. The nut contains a large seed packed in oakum and so protected by the strong hard shell that it is safe from the violence of the waves for long periods, voyaging from one island to another, landing and germinating.
Following the coconut many other seeds will make port, their germs protected by every kind of impermeable apparatus, their envelopes turned into boats by pockets of air. Some can sail for over a year and still germinate. Some have been known to cover three thousand miles before their pilgrimage was completed. Others will be shipped to our island on rafts of dead bamboo and sugar-cane, logs and other vegetable remains which glide along in the currents that encircle the seas and wash the shores. It is known that on rafts like these, rats and lizards, snails and slugs and ants have reached remote islands; and it is certain that such Arks likewise lend hospitality to seeds.
So much we might expect, and a good deal more, from the ocean as a means of transport for seeds. At the same time, while they have thus been arriving by sea, others will have confided their dissemination to the winds. For many kinds of plants send their fruits round the world by parachute. We have all seen the dandelion sailing off – its seed ballasting the most delicate aeronautical appliances. Such seeds may go a few yards or a few miles or hundreds of miles. There is no reason why we on our island might not expect a visit from that famous little creeping composite, Chevreulia stolonifera, which has been known to carry its message across five thousand five hundred miles from Montevideo to the island of Tristan da Cunha.
Many grasses would also arrive by air. I would hope to see the Spinifex squarrosus coming along. Its fruit looks like a porcupine. It can travel by air over four hundred miles, and if necessary cover part of its journey by sea – for the porcupine is so buoyant that it floats very lightly and spreads some of its spikes for sails. Such airborne arrivals would doubtless be followed or accompanied by various spores of mosses and ferns and orchids, travelling from fifty to nine hundred miles to join us.
Thus already our island has been considerably recruited with seeds arriving by water and air. A third service will also be employed, perhaps the most popular – namely, carriage by bird. The procedure is well known. First of all the seeds are introduced into the crop of the bird. To ensure this the plants hold up flags, called berries, to attract attention both as to presence and ripeness of fruit – the red flags being the most popular, though yellow, white, black, blue, and pink are used as the occasion demands. The bird eats the fruit but cannot digest the seed, which in due course will be passed out intact. Meanwhile, safely cabined, it can be charioted across ranges of mountains and arms of the sea. Since over forty different kinds of birds are said to eat any one species of fruit, this bird-mail, however irregular and haphazard in the delivery of its envelopes of seed can and does make a vast distribution throughout the world. Plants anxious to promote colonization in far distant realms charter birds that fly up to two thousand four hundred miles. But in this case the seeds do not reside inside but outside their vehicles. They adhere to the feathers by means of hooks and brackets and claws. Or they reside within clods of earth carried away by the birds – a ball of earth which had stuck in the feet of a bird, on being examined by Charles Darwin, was found to contain eighty-two seeds of five different species.
There is one bird which seems to specialize in its planting to such an extent that one might think it deliberate! This is the Eichelhäher in Germany – the name meaning acorn-carrier. It is a famous planter of oak trees. According to Herr Johannes W E Schmoll, it likes nothing better than to carry an acorn in its goitre and subsequently spit it out. It is said that wherever the Eichelhäher plants an acorn it flourishes, though foresters planting in the same area must risk the destruction of the seed by mice or boars: for the Eichelhäher’s acorn appears to be distasteful to all acorn-eating animals. The soil of the Grunewald in the Potsdam district was found to be poor for the cultivation of all but pine-trees, and the forestry commission planted only pine; but if you take a walk through the wood you sometimes come across lonely but mighty oaks, which were all planted, according to the foresters, by the Eichelhäher – whose call can often be heard in the district.
After about twenty years our island will have begun to display considerable vegetation in the shape of grasses, shrubs and even trees. It is not a particularly small island; it is over two hundred square miles, containing mountains, rivers, and plains. There is no feasible spot on this land which the vegetation will not attempt to inhabit; no fertile cranny or crevice into which it will not creep. Thus we must be prepared to see many more devices for transit.
If at any season of the year there are fields of ice or glaciers, then certain seeds like poppy, willow, and saxifrage will skate to a further place propelled on the wings of the wind. And plenty of others, with the wind behind them, will be blown across the plains, scattering seeds as they go and by stages of colonization carry their empire to the confines of the land.
Meanwhile the rivers and the floods will carry on the work of d
ispersal. At least ninety species will travel by water. Some will drift by themselves. Others, brought on to logs by ants, will be ferried for long distances. But there is one plant which is singular in the execution of its designs – the Lotus Lily. Growing by the side of a river, it creates a wooden basin on the top of its stalk in which the nuts reside. When the nuts are ripe the wooden cradle breaks off from the stalk and sails downstream. And as it travels the nuts germinate and the boat becomes a navigating nursery, a floating flower-pot.
We are assuming that by now this attractive island is by no means devoid of animals. Here is another means of plant distribution. According to the number of animals, we may count additional vehicles for seed. And again it is as if we saw determination, intelligence, will, deliberate contrivance to ensure means of transportation. We are all familiar with the simple burr that clings to our clothes in an embrace impossible to shake off. The burdock growing by the wayside or the goose-grass in the hedges fasten their fruits to anything that brushes against them, be it fur, feather, or cloth. There is a frightful plant called the Grapne which has harpoon-like spikes several inches long so that any animal lying on one will be driven frantic with pain and will gallop wildly about until it gets rid of it. Certain seeds exude a viscid or glutinous liquid so that they stick to an animal as with gum – to such an extent that a bird gorging on the species aculeata can be found lying helpless with its wings stuck together. And of course a sticky seed may adhere to a dead leaf and ride the wind as on a magic carpet.
A considerable number of animals are employed one way or another. The elephant, the alligator, the rhinoceros, the lizard, if handy, will serve; the grasshopper, the termite, and the ant are extremely useful; while the dormouse, the fieldmouse, and the squirrel are inveterate tree-planters, having a convenient habit of storing seed in the ground and then forgetting all about them. When the sky rains flesh and blood with a plague of locusts there will be another highly favoured means of migration. And, again, birds discharge their duty for short as well as long distances, sometimes whisking seeds from one spot to another at three hundred miles an hour. At the same time, more pedestrian-minded plants, such as the Cacti, may be seen to go by tortoise – perhaps winning the race in the end against another fruit mounted on a hare. The spores of fungi make their excursion by slug, changing later to toad, when they progress faster. Geraniums, stocks, and strawberries may employ the snail, advancing at the rate of one mile in twenty-two days. Some prefer to go by fish. Perch, eels, and cat-fish eat waterside plants and migrate down rivers – often changing from one river or lake to another. Any seed engaging this submarine service must be prepared to complete its expedition by air – that is, if in company with its vessel, it passes down the throat of an eagle, a stock, or a pelican. In the same way an orchid, starting its odyssey by earth-worm, will frequently continue by blackbird or thrush.
The Worm Forgives the Plough Page 29
