Chapter V: Part 5

As a preliminary canter I shall trot out first the valley of the Po, the existing mud flat best known by personal experience to the feet and eyes of the tweed-clad English tourist. Everybody who has looked down upon the wide Lombard plain from the pinnacled roof of Milan Cathedral, or who has passed by rail through that monotonous level of poplars and vines between Verona and Venice, knows well what a mud flat due to inundation and gradual silting up of a valley looks like. What I want to do now is to inquire into its origin, and to follow up in fancy the same process, still in action, till it has filled the Adriatic from end to end with one great cultivable lowland.

Once upon a time (I like to be at least as precise as a fairy tale in the matter of dates) there was no Lombardy. And that time was not, geologically speaking, so very remote; for the whole valley of the Po, from Turin to the sea, consists entirely of alluvial deposits--or, in other words, of Alpine mud--which has all accumulated where it now lies at a fairly recent period. We know it is recent, because no part of Italy has ever been submerged since it began to gather there. To put it more definitely, the entire mass has almost certainly been laid down since the first appearance of man on our earth: the earliest human beings who reached the Alps or the Apennines--black savages clad in skins of extinct wild beasts--must have looked down from their slopes, with shaded eyes, not on a level plain such as we see to-day, but on a great arm of the sea which stretched like a gulf far up towards the base of the hills about Turin and Rivoli. Of this ancient sea the Adriatic forms the still unsilted portion. In other words, the great gulf which now stops short at Trieste and Venice once washed the foot of the Alps and the Apennines to the Superga at Turin, covering the sites of Padua, Ferrara, Bologna, Ravenna, Mantua, Cremona, Modena, Parma, Piacenza, Pavia, Milan, and Novara. The industrious reader who gets out his Baedeker and looks up the shaded map of North Italy which forms its frontispiece will be rewarded for his pains by a better comprehension of the district thus demarcated. The idle must be content to take my word for what follows. I pledge them my honour that I'll do my best not to deceive their trustful innocence.

It may sound at first hearing a strange thing to say so, but the whole of that vast gulf, from Turin to Venice, has been entirely filled up within the human period by the mud sheet brought down by mountain torrents from the Alps and the Apennines.

A parallel elsewhere will make this easier of belief. You have looked down, no doubt, from the garden of the hotel at Glion upon the lake of Geneva and the valley of the Rhone about Villeneuve and Aigle. If so, you can understand from personal knowledge the first great stage in the mud-filling process; for you must have observed for yourself from that commanding height that the lake once extended a great deal farther up country towards Bex and St. Maurice than it does at present. You can still trace at once on either side the old mountainous banks, descending into the plain as abruptly and unmistakably as they still descend to the water's edge at Montreux and Vevey. But the silt of the Rhone, brought down in great sheets of glacier mud (about which more anon) from the Furca and the Jungfrau and the Monte Rosa chain, has completely filled in the upper nine miles of the old lake basin with a level mass of fertile alluvium. There is no doubt about the fact: you can see it for yourself with half an eye from that specular mount (to give the Devil his due, I quote Milton's Satan): the mud lies even from bank to bank, raised only a few inches above the level of the lake, and as lacustrine in effect as the veriest geologist on earth could wish it. Indeed, the process of filling up still continues unabated at the present day where the mud-laden Rhone enters the lake at Bouveret, to leave it again, clear and blue and beautiful, under the bridge at Geneva. The little delta which the river forms at its mouth shows the fresh mud in sheets gathering thick upon the bottom. Every day this new mud-bank pushes out farther and farther into the water, so that in process of time the whole basin will be filled in, and a level plain, like that which now spreads from Bex and Aigle to Villeneuve, will occupy the entire bed from Montreux to Geneva.

Turn mentally to the upper feeders of the Po itself, and you find the same causes equally in action. You have stopped at Pallanza--Garoni's is so comfortable. Well, then, you know how every Alpine stream, as it flows, full-gorged, into the Italian lakes, is busily engaged in filling them up as fast as ever it can with turbid mud from the uplands. The basins of Maggiore, Como, Lugano, and Garda are by origin deep hollows scooped out long since during the Great Ice Age by the pressure of huge glaciers that then spread far down into what is now the poplar-clad plain of Lombardy. But ever since the ice cleared away, and the torrents began to rush headlong down the deep gorges of the Val Leventina and the Val Maggia, the mud has been hard at work, doing its level best to fill those great ice-worn bowls up again. Near the mouth of each main stream it has already succeeded in spreading a fan-shaped delta. I will not insult you by asking you at the present time of day whether you have been over the St. Gothard. In this age of _trains de luxe_ I know to my cost everybody has been everywhere. No chance of pretending to superior knowledge about Japan or Honolulu; the tourist knows them. Very well, then; you must remember as you go past Bellinzona--revolutionary little Bellinzona with its three castled crags--you look down upon a vast mud flat by the mouth of the Ticino. Part of this mud flat is already solid land, but part is mere marsh or shifting quicksand. That is the first stage in the abolition of the lakes: the mud is annihilating them.

Maggiore, indeed, least fortunate of the three main sheets, is being attacked by the insidious foe at three points simultaneously. At the upper end, the Ticino, that furious radical river, has filled in a large arm, which once spread far away up the valley towards Bellinzona. A little lower down, the Maggia near Locarno carries in a fresh contribution of mud, which forms another fan-shaped delta, and stretches its ugly mass half across the lake, compelling the steamers to make a considerable detour eastward. This delta is rapidly extending into the open water, and will in time fill in the whole remaining space from bank to bank, cutting off the upper end of the lake about Locarno from the main basin by a partition of lowland. This upper end will then form a separate minor lake, and the Ticino will flow out of it across the intervening mud flat into the new and smaller Maggiore of our great-great-grandchildren. If you doubt it, look what the torrent of the Toce, the third assailing battalion of the persistent mud force, has already done in the neighbourhood of Pallanza. It has entirely cut off the upper end of the bay, that turns westward towards the Simplon, by a partition of mud; and this isolated upper bit forms now in our own day a separate lake, the Lago di Mergozzo, divided from the main sheet by an uninteresting mud bank. In process of time, no doubt, the whole of Maggiore will be similarly filled in by the advancing mud sheet, and will become a level alluvial plain, surrounded by mountains, and greatly admired by the astute Piedmontese cultivator.

What is going on in Maggiore is going on equally in all the other sub-Alpine lakes of the Po valley. They are being gradually filled in, every one of them, by the aggressive mud sheet. The upper end of Lugano, for example, has already been cut off, as the Lago del Piano, from the main body; and the _piano_ itself, from which the little isolated tarn takes its name, is the alluvial mud fiat of a lateral torrent--the mud flat, in fact, which the railway from Porlezza traverses for twenty minutes before it begins its steep and picturesque climb by successive zigzags over the mountains to Menaggio. Similarly the influx of the Adda at the upper end of Como has cut off the Lago di Mezzola from the main lake, and has formed the alluvial level that stretches so drearily all around Colico. Slowly the mud fiend encroaches everywhere on the lakes; and if you look for him when you go, there you can see him actually at work every spring under your very eyes, piling up fresh banks and deltas with alarming industry, and preparing (in a few hundred thousand years) to ruin the tourist trade of Cadenabbia and Bellagio.

If we turn from the lakes themselves to the Lombard plain at large, which is an immensely older and larger basin, we see traces of the same action on a vastly greater scale. A glance at the map will show the intelligent and ever courteous reader that the 'wandering Po'--I drop into poetry after Goldsmith--flows much nearer the foot of the Apennines than of the Alps in the course of its divagations, and seems purposely to bend away from the greater range of mountains. Why is this, since everything in nature must needs have a reason? Well, it is because, when the mud first began to accumulate in the old Lombard bay of the Adriatic, there was no Po at all, whether wandering or otherwise: the big river has slowly grown up in time by the union of the lateral torrents that pour down from either side, as the growth of the mud flat brought them gradually together. Careful study of a good map will show how this has happened, especially if it has the plains and mountains distinctively tinted after the excellent German fashion. The Ticino, the Adda, the Mincio, if you look at them close, reveal themselves as tributaries of the Po, which once flowed separately into the Lombard bay; the Adige, the Piave, the Tagliamento farther along the coast, reveal themselves equally as tributaries of the future Po, when once the great river shall have filled up with its mud the space between Trieste and Venice, though for the moment they empty themselves and their store of detritus into the open Adriatic.

Fix your eyes for a moment on Venetia proper, and you will see how this has all happened and is still happening. Each mountain torrent that leaps from the Tyrolese Alps bring down in its lap a rich mass of mud, which has gradually spread over a strip of sea some forty or fifty miles wide, from the base of the mountains to the modern coast-line of the province. Near the sea--or, in other words, at the temporary outlet--it forms banks and lagoons, of which those about Venice are the best known to tourists, though the least characteristic. For miles and miles between Venice and Trieste the shifting north shore of the Adriatic consists of nothing but such accumulating mud banks. Year after year they push farther seaward, and year after year fresh islets and shoals grow out into the waves beyond the temporary deltas. In time, therefore, the gathering mud banks of these Alpine torrents must join the greater mud bank that runs rapidly seaward at the delta of the Po. As soon as they do so the rivers must rush together, and what was once an independent stream, emptying itself into the Adriatic, must become a tributary of the Po, helping to swell the waters of that great united river. The Adige has now just reached this state: its delta is continuous with the delta of the Po, and their branches interosculate. The Mincio and the Adda reached it ages since: the Piave and the Livenia will not reach it for ages. In Roman days Hatria was still on the sea: it is now some fifteen miles inland.

From all this you can gather why the existing Po flows far from the Alps and nearer the base of the Apennines. The Alpine streams in far distant days brought down relatively large floods of glacial mud; formed relatively large deltas in the old Lombard bay; filled up with relative rapidity their larger half of the basin. The Apennines, less lofty, and free from glaciers, sent down shorter and smaller torrents, laden with far less mud, and capable therefore of doing but little alluvial work for the filling in of the future Lombardy. So the river was pushed southward by the Alpine deposits of the northern streams, leaving the great plains of Cisalpine Gaul spread away to the north of it.

And this land-making action is ceaseless and continuous. About Venice, Chioggia, Maestra, Comacchio, the delta of the Po is still spreading seaward. In the course of ages--if nothing unforeseen occurs meanwhile to prevent it--the Alpine mud will have filled in the entire Adriatic; and the Ionian Isles will spring like isolated mountain ridges from the Adriatic plain, as the Euganean hills--those 'mountains Euganean' where Shelley 'stood listening to the pæan with which the legioned rocks did hail the sun's uprise majestical'--spring in our own time from the dead level of Lombardy. Once they in turn were the Euganean islands, and even now to the trained eye of the historical observer they stand up island-like from the vast green plain that spreads flat around them.

Perhaps it seems to you a rather large order to be asked to believe that Lombardy and Venetia are nothing more than an outspread sheet of deep Alpine mud. Well, there is nothing so good for incredulity, don't you know, as capping the climax. If a man will not swallow an inch of fact, the best remedy is to make him gulp down an ell of it. And, indeed, the Lombard plain is but an insignificant mud flat compared with the vast alluvial plains of Asiatic and American rivers. The alluvium of the Euphrates, of the Mississippi, of the Hoang Ho, of the Amazons would take in many Lombardies and half-a-dozen Venetias without noticing the addition. But I will insist upon only one example--the rivers of India, which have formed the gigantic deep mud flat of the Ganges and the Jumna, one of the very biggest on earth, and that because the Himalayas are the highest and newest mountain chain exposed to denudation. For, as we saw foreshadowed in the case of the Alps and Apennines, the bigger the mountains on which we can draw the greater the resulting mass of alluvium. The Rocky Mountains give rise to the Missouri (which is the real Mississippi); the Andes give rise to Amazons and the La Plata; the Himalayas give rise to the Ganges and the Indus. Great mountain, great river, great resulting mud sheet.

At a very remote period, so long ago that we cannot reduce it to any common measure with our modern chronology, the southern table-land of India--the Deccan, as we call it--formed a great island like Australia, separated from the continent of Asia by a broad arm of the sea which occupied what is now the great plain of Bengal, the North-West, and the Punjaub. This ancient sea washed the foot of the Himalayas, and spread south thence for 600 miles to the base of the Vindhyas. But the Himalayas are high and clad with gigantic glaciers. Much ice grinds much mud on those snow-capped summits. The rivers that flowed from the Roof of the World carried down vast sheets of alluvium, which formed fans at their mouths, like the cones still deposited on a far smaller scale in the Lake of Geneva by little lateral torrents. Gradually the silt thus brought down accumulated on either side, till the rivers ran together into two great systems--one westward--the Indus, with its four great tributaries, Jhelum, Chenab, Ravee, Sutlej; one eastward, the Ganges, reinforced lower down by the sister streams of the Jumna and the Brahmapootra. The colossal accumulation of silt thus produced filled up at last all the great arm of the sea between the two mountain chains, and joined the Deccan by slow degrees to the continent of Asia. It is still engaged in filling up the Bay of Bengal on one side by the detritus of the Ganges, and the Arabian Sea on the other by the sand-banks of the Indus.

In the same way, no doubt, the silt of the Thames, the Humber, the Rhine, and the Meuse tend slowly (bar accidents) to fill up the North Sea, and anticipate Sir Edward Watkin by throwing a land bridge across the English Channel. If ever that should happen, then history will have repeated itself, for it is just so that the Deccan was joined to the mainland of Asia.

One question more. Whence comes the mud? The answer is, Mainly from the detritus of the mountains. There it has two origins. Part of it is glacial, part of it is leaf-mould. In order to feel we have really got to the very bottom of the mud problem--and we are nothing if not thorough--we must examine in brief these two separate origins.

The glacier mud is of a very simple nature. It is disintegrated rock, worn small by the enormous millstone of ice that rolls slowly over the bed, and deposited in part as 'terminal moraine' near the summer melting-point. It is the quantity of mud thus produced, and borne down by mountain torrents, that makes the alluvial plains collect so quickly at their base. The mud flats of the world are in large part the wear and tear of the eternal hills under the planing action of the eternal glaciers.

But let us be just to our friends. A large part is also due to the industrious earth-worm, whose place in nature Darwin first taught us to estimate at its proper worth. For there is much detritus and much first-rate soil even on hills not covered by glaciers. Some of this takes its origin, it is true, from disintegration by wind or rain, but much more is caused by the earth-worm in person. That friend of humanity, so little recognized in his true light, has a habit of drawing down leaves into his subterranean nest, and there eating them up, so as to convert their remains into vegetable mould in the form of worm-casts. This mould, the most precious of soils, gets dissolved again by the rain, and carried off in solution by the streams to the sea or the lowlands, where it helps to form the future cultivable area. At the same time the earthworms secrete an acid, which acts upon the bare surface of rock beneath, and helps to disintegrate it in preparation for plant life in unfavourable places. It is probable that we owe almost more on the whole to these unknown but conscientious and industrious annelids than even to those 'mills of God' the glaciers, of which the American poet justly observes that though they grind slowly, yet they grind exceedingly small.

In the last resort, then, it is mainly on mud that the life of humanity in all countries bases itself. Every great plain is the alluvial deposit of a great river, ultimately derived from a great mountain chain. The substance consists as a rule of the débris of torrents, which is often infertile, owing to its stoniness and its purely mineral character; but wherever it has lain long enough to be covered by earth-worms with a deep black layer of vegetable mould, there the resulting soil shows the surprising fruitfulness one gets (for example) in Lombardy, where twelve crops a year are sometimes taken from the meadows. Everywhere and always the amount and depth of the mud is the measure of possible fertility; and even where, as in the Great American Desert, want of water converts alluvial plains into arid stretches of sand-waste, the wilderness can be made to blossom like the rose in a very few years by artificial irrigation. The diversion of the Arkansas River has spread plenty over a vast sage scrub; the finest crops in the world are now raised over a tract of country which was once the terror of the traveller across the wild west of America.

THE GREENWOOD TREE.

It is a common, not to say a vulgar error, to believe that trees and plants grow out of the ground. And of course, having thus begun by calling it bad names, I will not for a moment insult the intelligence of my readers by supposing them to share so foolish a delusion. I beg to state from the outset that I write this article entirely for the benefit of Other People. You and I, O proverbially Candid and Intelligent One, it need hardly be said, are better informed. But Other People fall into such ridiculous blunders that it is just as well to put them on their guard beforehand against the insidious advance of false opinions. I have known otherwise good and estimable men, indeed, who for lack of sound early teaching on this point went to their graves with a confirmed belief in the terrestrial origin of all earthly vegetation. They were probably victims of what the Church in its succinct way describes and denounces as Invincible Ignorance.

Now, the reason why these deluded creatures supposed trees to grow out of the ground, instead of out of the air, is probably only because they saw their roots there.

Of course, when people see a wallflower rooted in the clefts of some old church tower, they don't jump at once to the inane conclusion that it is made of rock--that it derives its nourishment direct from the solid limestone; nor when they observe a barnacle hanging by its sucker to a ship's hull, do they imagine it to draw up its food incontinently from the copper bottom. But when they see that familiar pride of our country, a British oak, with its great underground buttresses spreading abroad through the soil in every direction, they infer at once that the buttresses are there, not--as is really the case--to support it and uphold it, but to drink in nutriment from the earth beneath, which is just about as capable of producing oak-wood as the copper plate on the ship's hull is capable of producing the flesh of a barnacle. Sundry familiar facts about manuring and watering, to which I will return later on, give a certain colour of reasonableness, it is true, to this mistaken inference. But how mistaken it really is for all that, a single and very familiar little experiment will easily show one.

Cut down that British oak with your Gladstonian axe; lop him of his branches; divide him into logs; pile him up into a pyramid; put a match to his base; in short, make a bonfire of him; and what becomes of robust majesty? He is reduced to ashes, you say. Ah, yes, but what proportion of him? Conduct your experiment carefully on a small scale; dry your wood well, and weigh it before burning; weigh your ash afterwards, and what will you find? Why, that the solid matter which remains after the burning is a mere infinitesimal fraction of the total weight: the greater part has gone off into the air, from whence it came, as carbonic acid. Dust to dust, ashes to ashes; but air to air, too, is the rule of nature.

It may sound startling--to Other People, I mean--but the simple truth remains, that trees and plants grow out of the atmosphere, not out of the ground. They are, in fact, solidified air; or to be more strictly correct, solidified gas--carbonic acid.

Take an ordinary soda-water syphon, with or without a wine-glassful of brandy, and empty it till only a few drops remain in the bottom. Then the bottle is full of gas; and that gas, which will rush out with a spurt when you press the knob, is the stuff that plants eat--the raw material of life, both animal and vegetable. The tree grows and lives by taking in the carbonic acid from the air, and solidifying its carbon; the animal grows and lives by taking the solidified carbon from the plant, and converting it once more into carbonic acid. That, in its ideally simple form, is the Iliad in a nutshell, the core and kernel of biology. The whole cycle of life is one eternal see-saw. First the plant collects its carbon compounds from the air in the oxidized state; it deoxidizes and rebuilds them: and then the animal proceeds to burn them up by slow combustion within his own body, and to turn them loose upon the air, once more oxidized. After which the plant starts again on the same round as before, and the animal also recommences _da capo_. And so on _ad infinitum_.

But the point which I want particularly to emphasize here is just this: that trees and plants don't grow out of the ground at all, as most people do vainly talk, but directly out of the air; and that when they die or get consumed, they return once more to the atmosphere from which they were taken. Trees undeniably eat carbon.

Of course, therefore, all the ordinary unscientific conceptions of how plants feed are absolutely erroneous. Vegetable physiology, indeed, got beyond these conceptions a good hundred years ago. But it usually takes a hundred years for the world at large to make up its leeway. Trees don't suck up their nutriment by the roots, they don't derive their food from the soil, they don't need to be fed, like babies through a tube, with terrestrial solids. The solitary instance of an orchid hung up by a string in a conservatory on a piece of bark, ought to be sufficient at once to dispel for ever this strange illusion--if people ever thought; but of course they don't think--I mean Other People. The true mouths and stomachs of plants are not to be found in the roots, but in the green leaves; their true food is not sucked up from the soil, but is inhaled through tiny channels from the air; the mass of their material is carbon, as we can all see visibly to the naked eye when a log of wood is reduced to charcoal: and that carbon the leaves themselves drink in, by a thousand small green mouths, from the atmosphere around them.

But how about the juice, the sap, the qualities of the soil, the manure required? is the incredulous cry of Other People. What is the use of the roots, and especially of the rootlets, if they are not the mouths and supply-tubes of the plants? Well, I plainly perceive I can get 'no forrarder,' like the farmer with his claret, till I've answered that question, provisionally at least; so I will say here at once, without further ado--the plant requires drink as well as food, and the roots are the mouths that supply it with water. They also suck up a few other things as well, which are necessary indeed, but far from forming the bulk of the nutriment. Many plants, however, don't need any roots at all, while none can get on without leaves as mouths and stomachs. That is to say, no true plantlike plants, for some parasitic plants are practically, to all intents and purposes, animals. To put it briefly, every plant has one set of aerial mouths to suck in carbon, and many plants have another set of subterranean mouths as well, to suck up water and mineral constituents.

Have you ever grown mustard and cress in the window on a piece of flannel? If so, that's a capital practical example of the comparative unimportance of soil, except as a means of supplying moisture. You put your flannel in a soup-plate by the dining-room window; you keep it well wet, and you lay the seeds of the cress on top of it. The young plants, being supplied with water by their roots, and with carbon by the air around, have all the little they need below, and grow and thrive in these conditions wonderfully. But if you were to cover them up with an air-tight glass case, so as to exclude fresh air, they'd shrivel up at once for want of carbon, which is their solid food, as water is their liquid.

The way the plant really eats is little known to gardeners, but very interesting. All over the lower surface of the green leaf lie scattered dozens of tiny mouths or apertures, each of them guarded by two small pursed-up lips which have a ridiculously human appearance when seen through a simple microscope. When the conditions of air and moisture are favourable, these lips open visible to admit gases; and then the tiny mouths suck in carbonic acid in abundance from the air around then. A series of pipes conveys the gaseous food thus supplied to the upper surface of the leaf, where the sunlight falls full upon it. Now, the cells of the leaf contain a peculiar green digestive material, which I regret to say has no simpler or more cheerful name than chlorophyll; and where the sunlight plays upon this mysterious chlorophyll, it severs the oxygen from the carbon in the carbonic acid, turns the free gas loose upon the atmosphere once more through the tiny mouths, and retains the severed carbon intact in its own tissues. That is the whole process of feeding in plants: they eat carbonic acid, digest it in their leaves, get rid of the oxygen with which it was formerly combined, and keep the carbon stored up for their own purposes.

Life as a whole depends entirely upon this property of chlorophyll; for every atom of organic matter in your body or mine was originally so manufactured by sunlight in the leaves of some plant from which, directly or indirectly, we derive it.

To be sure, in order to make up the various substances which compose their tissues--to build up their wood, their leaves, their fruits, their blossoms--plants require hydrogen, nitrogen, and even small quantities of oxygen as well; but these various materials are sufficiently supplied in the water which is taken up by the roots, and they really contribute very little indeed to the bulk of the tree, which consists for the most part of almost pure carbon. If you were to take a thoroughly dry piece of wood, and then drive off from it by heat these extraneous matters, you would find that the remainder, the pure charcoal, formed the bulk of the weight, the rest being for the most part very light and gaseous. Briefly put, plants are mostly carbon and water, and the carbon which forms their solid part is extracted direct from the air around them.

How does it come about then that a careless world in general, and more especially the happy-go-lucky race of gardeners and farmers in particular, who have to deal so much with plants in their practical aspect, always attach so great importance to root, soil, manure, minerals, and so little to the real gaseous food stuff of which their crops are, in fact, composed? Why does Hodge, who is so strong on grain and guano, know absolutely nothing about carbonic acid? That seems at first sight a difficult question to meet. But I think we can meet it with a simple analogy.

Oxygen is an absolute necessary of human life. Even food itself is hardly so important an element in our daily existence; for Succi, Dr. Tanner, the prophet Elijah, and other adventurous souls too numerous to mention, have abundantly shown us that a man can do without food altogether for forty days at a stretch, while he can't do without oxygen for a single minute. Cut off his supply of that life-supporting gas, choke him, or suffocate him, or place him in an atmosphere of pure carbonic acid, or hold his head in a bucket of water, and he dies at once. Yet, except in mines or submarine tunnels, nobody ever takes into account practically this most important factor in human and animal life. We toil for bread, but we ignore the supply of oxygen. And why? Simply because oxygen is universally diffused everywhere. It costs nothing. Only in the Black Hole of Calcutta or in a broken tunnel shaft do men ever begin to find themselves practically short of that life-sustaining gas, and then they know the want of it far sooner and far more sharply than they know the want of food on a shipwreck raft, or the want of water in the thirsty desert. Yet antiquity never even heard of oxygen. A prime necessary of life passed unnoticed for ages in human history, only because there was abundance of it to be had everywhere.

Now it isn't quite the same, I admit, with the carbonaceous food of plants. Carbonic acid isn't quite so universally distributed as oxygen, nor can every plant always get as much as it wants of it. I shall show by-and-by that a real struggle for food takes place between plants, exactly as it takes place between animals; and that certain plants, like Oliver Twist in the workhouse, never practically get enough to eat. Still, carbonic acid is present in very large quantities in the air in most situations, and is freely brought by the wind to all the open spaces which alone man uses for his crops and his gardening. The most important element in the food of plants is thus in effect almost everywhere available, especially from the point of view of the mere practical everyday human agriculturist. The wind that bloweth where it listeth brings fresh supplies of carbon on its wings with every breeze to the mouths and throats of the greedy and eager plants that long to absorb it.

It is quite otherwise, however, with the soil and its constituents. Land, we all know--or if we don't, it isn't the fault of Mr. George and Mr. A.R. Wallace--land is 'naturally limited in quantity.' Every plant therefore struggles for a foothold in the soil far more fiercely and far more tenaciously than it struggles for its share in the free air of heaven. Your plant is a land-grabber of Rob Roy proclivities; it believes in a fair fight and no favour. A sufficient supply of food it almost takes for granted, if only it can once gain a sufficient ground-space. But other plants are competing with it, tooth and nail (if plants may be permitted by courtesy those metaphorical adjuncts), for their share of the soil, like crofters or socialists; every spare inch of earth is permeated and pervaded with matted fibres; and each is striving to withdraw from each the small modicum of moisture, mineral matter, and manure for which all alike are eagerly battling.

Now, what the plant wants from the soil is three things. First and foremost it wants support; like all the rest of us it must have its _pou sto_, its _pied-à-terre_, its _locus standi_. It can't hang aloft, like Mahomet's coffin, miraculously suspended on an aerial perch between earth and heaven. Secondly, it wants water, and this it can take in, as a rule, only or mainly by means of the rootlets, though there are some peculiar plants which grow (not parasitically) on the branches of trees, and absorb all the moisture they need by pores on their surface. And thirdly, it wants small quantities of nitrogenous matter--in the simpler language of everyday life called manure--as well as of mineral matter--in the simpler language of everyday life called ashes. It is mainly the first of these three, support, that the farmer thinks of when he calculates crops and acreage; for the second, he depends upon rainfall or irrigation; but the third, manure, he can supply artificially; and as manure makes a great deal of incidental difference to some of his crops, especially corn--which requires abundant phosphates--he is apt to over-estimate vastly its importance from a theoretical point of view.

Besides, look at it in another light. Over large areas together, the 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.