The Romance of Plant Life

In some Sarracenias the vase is brought up into a sort of hood or dome with the entrance at one side and below. There are thin patches on this dome or cupola, and small insects, attracted by the light which comes through these bare places, remain dashing themselves against them or crawling over them just as flies do on a window-pane, until they become tired and fall down into the water below.

There is something horrible in the cold and careful way in which this plant arranges its baits for "confiding insects. The latter are fed with honey, even on the very border of the assassin's den, but after this farewell revel they generally slip upon the smooth edge, and are hurled, like lost souls, down into the abyss."150

In another plant, the Pitcher Plant (Nepenthes, so called from the drug which produces the sleep of death), we find an even more beautifully arranged pitcher which acts in very much the same way. It is, however, only the end of a rather long leaf, or rather of its midrib, that is turned up to act as a pitcher. There are similar stiff hairs pointing downwards, and honey is plentifully secreted. But, in Nepenthes, there is also a distinct secretion which digests the bodies of the drowning insects. The ferment resembles the active principle of the gastric and pancreatic juices of the human body, and, as acids are also present, the insect's body becomes changed into nutritious juices which readily diffuse into the plant.151 Dr. Macfarlane found that when the pitchers were stimulated by being given insects, the liquid inside them could digest fibrin to jelly in from three-quarters to one hour's time.152 But certain insects have somehow managed to educate their larvæ to resist the gastric juices of Nepenthes.

Near Fort Dauphin, in Madagascar, I found great quantities of Nepenthes madagascariensis. Almost every pitcher was one-third to two-thirds full of corpses, but in some of them large, fat, white maggots, of a very unprepossessing appearance, were quite alive and apparently thriving. These must have been the larvæ of a blowfly similar to that which has been mentioned by others as inhabiting Sarracenia. At the same place a white spider was very often to be seen. Its web was spun across the mouth of a pitcher, and its body was quite invisible against the bleached remains inside.

It had suited its colour to the corpses within, in order that it might steal from the Nepenthes the due reward of all its ingenious contrivances!

A totally different arrangement is found in an inconspicuous and ugly little marsh and ditch plant called Utricularia or Bladderwort. It is very difficult to see, for unless it happens to be in flower it is entirely submerged in the water. The flowers, which are purple, are conspicuous and easily seen even at a distance. On these submerged leaves there are hundreds of small bladders. They are about the size of a pea, and are most ingeniously contrived to catch small water-animalcula. The general idea of the bladderwort is exactly that of the eel-pots so common in some parts of the Thames. There is a small flap which acts as a trapdoor. Small creatures probably take refuge in the bladders when pursued by the larger water-fleas, etc., for it must seem to them to be a safe and secure retreat.

But once within the door, they are imprisoned and cannot find their way out again. They perish inside and their bodies are digested by the plant; on the inside of the bladder there are gland hairs which also secrete a digestive fluid.

The bladderwort is dangerous to fish, for the little fry, when quite small, run their heads and gills into the bladders and are suffocated.

There are a great many kinds of Utricularia, and they occur in most of the great floral regions.

One of them has chosen a very extraordinary and curious situation. It lives inside the little cups of water which, as we have already mentioned, are formed by the leaves of some Bromeliads. The insects in the water which ought to nourish the Bromeliad (Tillandsia) are really used by the Utricularia. Other Utricularias live in damp earth, moss, etc.

It is not only by traps and pitfalls that plants catch insects: many have specially modified hairs which are quite efficient insect-catchers.

Hairs are used by plants for many different purposes, and it is rather interesting to see how quite a simple organ like a hair can be altered. The stinging hair of the nettle has already been mentioned; many grasses possess minute, rough, flinty hairs, which probably prevent snails from eating them. That also is probably the reason of the strong, rough, coarse hairs which cover the Borage and the Comfrey.

Then on the Chickweed and the Bird's-eye Speedwell there are lines of rather long, flexible hairs which at first sight appear to be of no use at all. But if you take either of these plants, and, holding it upright, place a large drop of water on the leaves, you will see that these hairs are intended to carry the water down the stem. The water runs along them. It is a very pretty little experiment, especially if done in artificial light, so that these hairs are, like the root hairs, intended to absorb or suck up water as it passes over them. Then the Edelweiss and the Lammie's Lug (Stachys lanata) are entirely covered with white cotton-woolly hairs: these are intended to keep the water in the plant, and do so as effectually as a rough woollen coat will keep out rain and mist. Silky hairs, downy hairs, and others are found wrapping up the tiny baby leaves in the bud: they probably keep them warm, and perplex and ward off objectionable insects.

But, perhaps, the sticky or glutinous hairs are the most wonderful of all. They are found on many plants, such as Salvia glutinosa,153 Plumbago, and Catchfly. One can see insects stuck on them and vainly struggling to be free, and the hairs undoubtedly prevent green-fly and other such pests from interfering with the honey of the flower. In some of these cases it has been shown that the body of the insect is actually used as food, but that is more obvious with two interesting plants which specially devote themselves to the capture of insect prey. One of these is very often kept in the Boer farmhouses near Tulbagh, in South Africa, simply to attract the flies, which are a perfect pest in those dry valleys. Another Drosophyllum, the Fly-Catcher, grows on sandy and rocky ground in Portugal and Morocco. This is also used by the peasants near Oporto as a convenient fly-paper.

In both of these plants large drops of a sticky, glistening liquid are secreted by the hairs which cover the leaves. Any small insect alighting on the latter is sure to get covered by the liquid, and in trying to get away will become hopelessly involved in it. It is probably soon suffocated, for the gummy matter will choke the small air-holes by which it breathes. Both these plants are said to secrete both an acid and a digestive secretion.

But we have two plants which are even more interesting in this country.

Walking over the rough marshy pastures or moors of Scotland one is sure to notice, generally on wet peaty and barren soil, a little rosette of bright, yellow-green, glistening leaves. If it is the right season there will be a handsome purple flower whose stalk springs from them. This is the Butterwort (Pinguicula), and it is not a bad name, for the leaves remind one of butter. The whole upper surface of the leaves is covered with tiny glands secreting a sticky, glistening matter. It is said that there will be as many as fifty thousand of these glands on a square inch of the upper surface.

Now in such places every one knows that there are quantities of midges, and also that these insects are always exceedingly thirsty. They prefer blood, it is true, but when they see these bright yellowish leaves they naturally go to them. When, however, the midge touches the leaf, the sticky liquid clings to its wings and legs, and it cannot escape.

So far this does not differ from the Fly Catchers mentioned above, but another very curious action then begins. If the midge or fly is near the margin of the leaf, the edge of the latter begins to curl or roll inwards over it. It does so very slowly, and may not finish rolling over the insect for some hours. Whilst this is going on acids and "gastric juice," or ferments which act in the same way, are being poured over the body of the midge, which is finally completely digested. Next day, having finished the midge, the leaf majestically unrolls itself again and waits for another.

The juice contains rennet, and is used by the Lapps in making a horrible delicacy called Tätmiölk. It has also been used by the Swiss shepherds for at least two hundred years, to cure sores on cows' udders.

The other British plant is the Sundew (Drosera). Every one who has been on peat-mosses and moors probably knows its little reddish rosettes of small rounded or spoon-shaped leaves lying on bare peat or wet mossy ground. Each leaf seems to be covered by hundreds of glittering little dewdrops (whence the name).

The hairs or tentacles which cover the leaf secrete this glistening, sticky fluid. There must be about two hundred of them on a single leaf.

An insect flying about near the Sundew is sure to be attracted by the conspicuous glittering, reddish leaves, and probably alights upon it. Then it finds itself caught and begins to struggle, but this simply brings it against more tentacles.

Now happens the most wonderful part of the whole performance. All the neighbouring tentacles, although they have not been touched, bend over towards the struggling insect and pin it down in the middle of the leaf. They do not bend over very quickly. In two or three minutes they will bend over towards it through an angle of forty-five degrees, and it takes them ten minutes to bend over ninety degrees.

There is something rather horrible in the sight of a large insect struggling with these slow, remorseless, well-aimed tentacles; most people free the insect unless, at least, it happens to be a midge. The point which is so difficult to understand is to know how those untouched tentacles know that the insect is there and exactly where it is. There is no doubt that they do know, for they behave exactly as if they were the arms of a spider.

If you put two insects on either side of the middle of the leaf, half the tentacles will pin down one and the other half will deal with the other insect.

At the same time acids and ferments are poured out which digest the insect. It takes about two days for a leaf to finish off an insect, and then the tentacles again unclose.

Moreover it is difficult to deceive those tentacles. They will bend in for the tiniest piece of useful substance; for instance, a length of one-seventy-fifth of an inch of woman's hair will make them secrete digestive fluid. One millionth part of a pound of ammonium phosphate will also produce secretion. But a shower of heavy rain, grains of sand, or other useless material, will not cause any secretion, and even if they do bend in a little, they soon discover their mistake and stand out again. If you try the same experiment under a bell-glass from which the oxygen has been withdrawn by an air-pump, nothing happens; or if you chloroform the Sundew it will pay no attention to small pieces of meat until it recovers from the effects of the chloroform.

When these Droseras are taken to a greenhouse and experiments are made on them, they run into very great danger. They are almost certain to die of overfeeding or indigestion. It is impossible to keep people from giving them too much to eat.

This wonderful little plant shows quite distinctly that there must be some way of sending messages in its leaves. Somehow the message travels from the tentacle which the fly has touched, down the stalk into the leaf, and up into the other tentacles, and tells them that there is something worth stooping for.

No one has explained this, and probably no one will ever do so.

The last, and in some ways the most interesting, of all these carnivorous plants is Venus' Fly-trap (Dionæa muscipula), which grows in North America from Rhode Island to Florida.

It is a quite small herb with a small circle of leaves which lie flat on the ground. Each leaf ends in a nearly circular piece which is divided by a very marked midrib. The two semicircular halves have a series of teeth along their edges; these margin teeth are stiff and a little bent upwards. In the centre of each half there are three small hairs. On looking closely at these hairs one finds that each has a joint near the base; all over the centre of these leaf halves there are scattered glands which secrete ferments intended to digest any animal matter.

The really interesting point is connected with these central jointed or trigger hairs; they are extremely sensitive. But when they are touched it is not they themselves that are affected, but the entire circular end of the leaf!

Suppose an insect wanders on to the leaf and reaches one of these semicircular halves, nothing happens until it touches one of these hairs, but then both halves suddenly close together, exactly like an ordinary rat-trap! The teeth on the edges of the halves interlock like the teeth of a trap, and the insect is caught and imprisoned.

Its body is slowly digested away and goes to nourish the plant. The use of the joint in the sensitive hairs can be easily perceived, for when the two halves shut up together, the hairs fold down exactly like the funnel of a river steamboat when it passes under a bridge.

The closing of the two halves, which has been well compared to shutting up a half-open book, is very quick, as it does not take more than ten to thirty seconds. There is an abundant flow of "gastric juice," but the leaf takes a long time to digest its food. It may require three weeks to finish one insect. Moreover, if overfed, it may turn a bilious or dyspeptic yellow colour, and wither or even die. It only shuts for a short time if a grain of sand touches the sensitive hair, and, like Drosera, is not deceived in its food.

The Dionæa, Drosera, the Sensitive Plant, Mimulus, Barberry, and others, all show us clearly that plants somehow or other act as if they were conscious of what they ought to do. In fact, in all these cases, it is scarcely possible to help believing in some sort of rudimentary nervous system. At any rate Wordsworth comes near this belief, for he has written: —

"It is my faith, that every flower that blowsEnjoys the air it breathes."

CHAPTER XXVIII

MOSSES AND MOORS

Peat-mosses and their birds – Moorlands – Cotton-grass – Scotch whisky – Growth of peat-moss – A vegetable pump – Low-lying and moorland mosses – Eruptions and floods of peat – Colonizing by heather and Scotch fir – Peat-mosses as museums – Remains of children and troopers – Irish elk – Story of the plants in Denmark – Rhododendrons and peat – Uses of peat – Reclaiming the mosses near Glasgow.

IN Great Britain in this present year one finds exceedingly few places where the influence of man cannot be traced. Over most of the country, indeed, it is impossible to discover a single acre of land where Nature has been allowed to go on working at her own sweet will without interference or restraint.

But near Stirling, between the Lake of Monteith and the sea, there is a wide, desolate valley which is probably in exactly the same condition as it was when the Roman legions halted to reconnoitre before Agricola passed onwards to Perth and Aberdeen.

Indeed, this great peat-moss has been probably in very much the same condition for some 200,000 years, which is a nice round number to represent the ages that have passed since the Great Ice Age.

Now, as then, it is inexpressibly dreary and desolate; everywhere saturated with water, and only to be traversed in dry seasons and with much agility. Even with the greatest care the pedestrian may sink to the waist in a hole of black, slimy, peaty water. Moss, Heather clumps, Sedges, Rushes, and occasionally Cotton-grass, almost at one dead level, stretch right across from the one side of the huge valley to the other.

Even grouse are not common. In summer great numbers of gulls lay their eggs upon the moss. This also is one of the few places in Britain where great flocks of wild geese can be heard and seen, but only at a distance.

It is almost impossible to get near them, for the upright neck of the sentinel cannot be seen by the stalker as he wriggles towards the flock on his face, until long after the stalker himself has been plainly visible to the bird.

Of all useless stretches of barren waste, such a moss as this seems one of the worst. It would, of course, be possible to reclaim it; probably, fertile fields and rich meadows could be formed over the whole valley, but it would not pay nowadays. There is so much good land available in Canada, the United States, and Australia, that this great stretch of our native country will probably remain as useless as it was in Agricola's days.

In the Scottish Lowlands and Highlands the moorlands are almost as desolate. At a height of 1500 to 1600 feet in Southern Scotland there is nothing to be seen but the undulating lines of hills, all dark purple with heather or with the peculiar scorched reddish green of Deer's Hair and dried sedges.

Perhaps on the nearer hills small streams may have cut a whole series of intersecting ravines in the black peat. They may be six to ten feet deep, and here and there the bleached white stones which underlie them are exposed. Now and then the "kuk-kuk-kuk" of an irate cock grouse, and much too frequently the melancholy squawking of the curlew, irritates the pedestrian as he stumbles over clumps of heather, plunges in and out of the mossy holes, or circumvents impossible peat-haggs.

It is indeed a remarkable fact that though these islands support 44,000,000 of inhabitants, including at least 1,000,000 paupers and unemployed, one-seventh of Ireland and many square miles in Scotland are still useless peat-bogs!

The Bog of Allen alone covers 238,500 acres, and the peat is twenty-five feet deep.

In some few places the peat is still used for fuel, and there is a theory to the effect that peat reek is necessary for the best kinds of Scotch whisky, but neither grouse nor black-faced sheep, which live on the young shoots of the heather, employ in at all a satisfactory way these great stretches of land.

Many attempts have been made to spin the silky threads of the Cotton-grass which grows abundantly on the Scotch lowlands. It is neither a grass, nor does it supply cotton, but is called Eriophorum. It is perhaps the one really beautiful plant to be found on them, for its waving heads of fine silky-white hairs are exceedingly pretty.

The heather itself gives a splendid red and purple shade, which in summer and autumn is always changing colour, but it is monotonous. Neither the little Bog Asphodel with its yellowish flowers, nor red Drosera, or butter-coloured Butterwort, are particularly beautiful.

After seeing such a country one understands something of the Cameronian Covenanters who held their conventicles and took refuge therein.

The manner in which these mosses and moors have developed is most interesting, and yet difficult to explain.

There are two kinds of peat-mosses, which, although there are many intermediate types, may be kept apart.

The first, like the one near Stirling, Lochar and Solway Moss, near Dumfries, and Linwood, near Glasgow, have been formed in low-lying flat estuarine marshes.

If one refers back to page 210, it will be seen how reeds and rushes and marsh plants may gradually fill up river backwaters. Eventually a saturated, marshy meadow is produced.

Then comes the chance of that wonderful moss the peat-moss, or Sphagnum. It is scarcely possible to appreciate its structure without the help of a microscope and a good deal of trouble in the way of imagination.

It is in a small way a sort of vegetable pump which raises water a few inches or so. Stem and leaves and branches possess little cistern cells, which act both as capillary tubes raising the water and also retain it. The stems are upright and develop many branches, so that they become a close-ranked or serried carpet of upright moss-stems squeezed together, which floats on the surface of the water. Each moss-stem is growing upwards and dying off below. In consequence, the bottom gets filled up by dead mossy pieces, which accumulate there, while the live moss-carpet remains floating on the surface of the loathly, black, peaty water.

In many peat-mosses the water gets entirely filled up, but that does not stop the formation of the peat-moss. It is now resting on the water-saturated remains of its forefathers, and if water is abundantly supplied it goes on developing.

Thus in these lowland or estuarine peat-mosses the moss eventually occupies the water, and goes on growing. After this it develops like the moorland mosses which cover most of the Lowlands and Highlands of Scotland. They cover the hills, and it looks exactly as if some giant had plastered all those hills with a layer of six to ten feet of black peat from 1250 feet upwards.

The soil would at first be covered by a saturated moss-carpet of Sphagnum and other mosses. Rainwater falling upon it was all retained, and very little could get away, for the Sphagnum carpet is just like a huge sponge soaking up and retaining the water.

But it sometimes happens in these great upland mosses that there are enormous falls of rain which continue for days. Then the water collects under the living moss-carpet and over the dead peat. It may be gathered together in such quantities that the carpet of living peat above it bursts, and a deluge of peaty water overflows the surrounding country, destroying and spoiling everything that it encounters.

The worst of these inundations of black mud that has happened in recent years was in December, 1896, near Rathmore, where 200 acres of bog burst and a horrible river of mud overflowed the country for ten miles. Nine people perished, and enormous destruction was caused.

There have been many other cases. In 1824 Crowhill Bog, near Keighley, burst; and in 1745, in Lancashire, a space a mile long and half a mile broad was covered by peaty mud. There was also a case in 1697, where forty acres of bog at Charleville burst in the same way.154

Attempts have often been made to calculate the rate of growth of such peat-mosses. A great many of them began to develop on the mud left by the ice-sheet when the glaciers retreated at the end of the Ice Age. Those mosses are therefore probably 200,000 years old. Some of our Scotch mosses are twenty to twenty-five feet in depth, which gives a foot in 10,000 years. By calculation of the weight of the peat formed, Aigner made out that a certain moss was 20,600 years old, and was growing at the rate of two inches in a century.

But in Denmark ten feet has been formed in 250 to 300 years, and in Switzerland three to four feet of peat-moss has been formed in twenty-four years.

This shows quite distinctly that there is no regular rate of growth, and indeed it is obvious that much must depend on the climate, on the rainfall, on the drainage, and other circumstances.

Sooner or later, however, a limit comes to the growth of the moss. The surface then becomes gently curved: it is highest in the centre, and slopes very gently down in every direction to the edges.

What happens next? The first sign is that the surface begins to dry up, and Heather, with grey Cladonia lichens, begins to grow on the projecting tufts and tussocks.

Occasionally, if gulls build their nests on such drying-up mosses, patches of bright green grass appear wherever the gulls are in the habit of resting. That is due to the lime in their guano.

But under quite natural conditions a much more important and interesting change begins.

Here and there scattered over the moss, miserable little seedling Birches and Scotch Firs begin to struggle for life. Of course, if there are hares and rabbits, or if sheep and cattle are allowed to graze upon the moss, those firs have no chance whatever. They are eaten down to the ground.

But if allowed to go on growing they would no doubt cover the whole moss with a wood of Birch and Scotch Fir. In time that wood would by its roots and its formation of fine leaf-mould so radically alter the ground that a forest of Oaks might be possible.