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Romance of Plant Life

<h2>CHAPTER XXVI PLANTS WHICH PREY ON PLANTS</h2> The kinds of cannibals—Bacteria—Spring flowers—Pale, ghostly Wood-flowers—Their alliance with fungi—Gooseberries growing on trees—Orchid-hunting—The life of an orchid—The mistletoe—Balder the Beautiful—Druids—Mistletoe as a remedy—Its parasitic roots—The trees it prefers—The Cactus Loranthus—Yellow Rattle and Eyebright, or Milk-thief, and their root-suckers—Broomrape and toothwort—Their colour and tastes—The scales of the toothwort which catch animalcula—Sir Stamford Raffles—A flower a yard across—The Dodder—Its twining stem and sucker-roots—Parasites rare, degenerate and dangerously situated. THE word cannibal is often used in a very loose and unscientific way. Amongst some savage tribes it is the custom to eat old people and young children; but this is only in seasons of famine and scarcity, when there is no other food available, and not because they are specially fond of them. But amongst other tribes wars are made for the special purpose of capturing fat young people to cook. Sometimes they have become so accustomed to such delicacies that they are unable to get their food in any other way. Of course, when tribes become "pure cannibals" of this last type they have to be destroyed like wild beasts. Among plants we find all sorts of transitions and degrees of cannibalism. There are plants which sometimes, and, as it were, accidentally, attack others. But there are also real cannibal plants which live entirely on the life-juices and 328 sap of other plants, and cannot exist by their own labours at all. Moreover, we can find almost every conceivable state of transition. These can be clearly and definitely traced from those plants which depend on the labour of their own roots and leaves to others which have no leaves, and which consist merely of one large flower and a large adhesive sucker fixed on some one else's root. The difficulty is very often to know where to draw the line. Probably no flowering plant is quite independent of the labour and work of its neighbours. As we have tried to show in another chapter, a long preliminary cultivation by bacteria, lichens, and mosses is required before flowering plants can develop on bare rock. That is also necessary in all cases where the soil is mineral or inorganic, without any organic dust or fragments of vegetable or animal matter. Bacteria must always begin the work by preparing nitrates and other salts. So that only those bacteria which weather rocks can be called really free and independent. But other bacteria, such as those which cause typhoid, anthrax, hydrophobia, etc., are the best possible examples of pure cannibals, or, as they are usually described, parasites. This last word is derived from a peculiar class of people in ancient classical times, who used to appear whenever a meal was going to begin, and received food without giving anything in return. They are represented by our tramps or by the "sundowners" in Australia, who appear as soon as the evening meal is ready and when there is no possibility of going any further on their journey. The way in which plants became parasites or cannibals is a very interesting part of plant life, and we shall try to trace some of the various stages. 329 To begin with, if one looks out for them in spring one is sure to find a whole series of beautiful spring flowers. There is the Primrose, with its bright, hardy, yellow flowers; the Violet, whose strong perfume much annoys the huntsman, for it spoils the "scent" and shows him that the end of winter has come; the delicate little Moschatel, the Lesser Celandine, the Bluebell or Hyacinth, Dog's Mercury, the Male and the Lady Fern, and many others. Most of these begin to grow and are in flower early in the season. That is because they are living on the dead leaves of the last year, or rather of two or three years ago. Their roots are breaking up and devouring, with the help of worms, beetles, and insects, the leaf-mould of past seasons. They are quite dependent on the trees; they cannot exist except where such leaf-mould is formed. But it is very difficult to tell whether these humble little herbs which live on the scraps that fall from the tall trees are either parasites or clients, which last do some good in return for their share. Probably they are distinctly useful and good for the forest if this is considered as a whole establishment. They use light which would otherwise be wasted, and their own dead leaves increase the annual deposit of leaf-mould. There are other plants, such as the Bird's-nest (Neottia) and Coralroot[144] Orchids, as well as Monotropa and others, which also live on the rich, decaying leaf-mould of forests, but these are generally pale in colour, for they possess but little green chlorophyll. They are more directly dependent on the mould and have ceased to do much work for themselves. 330 Most of them in fact have entered into an alliance with fungi, and use these fungi to get their food material from the dead leaves. Such fungi are always abundant in good, well-grown forests (see p. 86). These Orchids and Monotropa have their roots and underground stems covered and wrapped round by the fungus threads, which extend from them in every direction, breaking up and decomposing the dead leaves. The colour of Monotropa is a pale waxen yellow, that of the others is usually a ghostly pale, opalescent, steel-blue or coral-like hue, which makes them very distinct in the dim, mysterious shades of the forest. These plants are undoubtedly of use, for they break up and decompose the leaf-mould. Another very interesting group are not well represented in this country. Sometimes one may see on an old tree a Gooseberry bush in full foliage quite high up the trunk in the fork of the branches. In sheltered woody ravines, Polypody ferns are often established on old moss-clad branches, where their green fronds hang over to catch as much as they can of the sunlight. But Orchids, Bromeliads, and Ferns which grow upon the branches of great trees are one of the most conspicuous and beautiful features of tropical woods. It is for these tree-orchids that the orchid-hunter braves the head-hunters of Borneo or traverses the precipices and rugged forests of Guatemala and Brazil. It is often necessary to cut down a tall tree in order to get the orchids in its higher branches. Often, however, this is unsuccessful, for the tree is so held up by creepers and other giants of the forest that it never reaches the ground! <div></div> <div class="figcenter"> <ANTIMG class="mw" src="images/i_331.jpg" alt="" /> <div class="caption"> PhotoSkeen and Co. Cinnamon Peeling in Ceylon </div> </div> Then, after being stripped from the branches, in some 331 out-of-the-way forest-clad range of Burma, Celebes, South America, or Madagascar, these orchids are dried, put up in crates and packed off to London, where they are carefully cultivated in hot-houses and persuaded to flower. They may be worth sixpence or they may be worth £500 each, but no one can tell until they have flowered in London. But the romance of the orchid-hunter is not exactly what we have to describe here. It is rather the romance of the life of the orchid itself. It is perched high up on the branches of the tallest trees in the forest, exposed to sun, exposed to wind, and quite unable to gather either salts or rain from the soil. How, then, does it manage to live? These orchids, it must be remembered, are only found in out-of-the-way and feverish, unhealthy places, where the aboriginal savages still lurk and endure a dreadful existence of hunger and starvation in dense tropical forests. Now the word "dense" explains the whole story. Those forests are so thick, so full of giant trees and exuberant growth, that civilized man even to-day in 1906 can make nothing of them, and leaves them to the savage. The reason why vegetation is so luxuriant is simply that there are both plentiful moisture and a hot, tropical sun. That makes the life of the orchid possible, and also ensures malaria for the hunter. It hangs out into the moist air long pendulous roots which act as so many sponges absorbing and soaking in moisture. The tremendous energy of growth covers bark and branches with creeping plants innumerable, with a profusion of moss, liverworts, and ferns such as we cannot imagine from our own experiences in this country. So the roots of our orchid find on the branches rich leaf-mould, 332 and it lives happily and contentedly on the salts and moisture accumulated by the mosses and other plants. Its leaves are fleshy and succulent, rather like those of a desert plant, so that it can store up water against a season of drought. These plants which grow in this way on other plants, do not, as a rule, greatly injure them, but many have not stopped at this stage. Take, for instance, the Gooseberry growing in the fork of an old tree. Some bird has been eating gooseberries and dropped the seed there. The roots of the gooseberry will grow down into the rotten part of the trunk. Earth and leaf-mould will accumulate there, and it is quite probable that the whole inside of the tree will decay away. The roots of the gooseberry will, if only indirectly, help in this decay. But it is far otherwise with another set of plants—the Mistletoe and its allies. There is plenty of romance connected with the mistletoe. Dr. M. T. Masters says as follows: "The origin of the modern custom connected with mistletoe is not very clear. Like many other customs, its original significance is only guessed at. If known, perhaps, the innocent merriment now associated with the plant would be exchanged for a feeling of stern disapproval, and the mistletoe would be banished from our homes. In such a case ignorance is bliss." It will be remembered that all the gods of Iceland were once gathered together so that a general oath might be exacted of every plant "that grew upon the earth," that they would do no harm to Balder the Beautiful. The Mistletoe did not take the oath, because it does not grow upon the earth but upon a tree. Then the enemy fashioned an arrow out of the mistletoe, and killed Balder. 333 There is a modern idea that the story is a myth representing the death of Spring, for a great many similar stories occur in widely distant places. However, it seems pretty certain that the plant was a sacred one to the Druids in the time of the Romans. Ovid speaks of this in the line, "Ad Viscum Druidæ cantare solebant." At their solemn meetings, which were held in remote sacred groves, a Druid clad in white robes cut the mistletoe with a golden sickle. Then, apparently, human sacrifices were offered and a general festival took place. Some remnant of this custom seems to have persisted in Herefordshire until recent times, for the tune "Hey derry down, down down derry" (which means in a circle move we round the oak) is supposed to be a relic of the hymn chanted by the Druids when they had found mistletoe on the oak. It was said in the Middle Ages to be a useful cure for apoplexy, madness, and giddiness. That is not at present the general view. Indeed, under present conditions it might conceivably promote the last and even the second of these disorders, though in an agreeable way! The Mistletoe and its allies, Loranthus and Arceuthobium, grow upon the branches of trees like the orchids and gooseberries already mentioned, but they differ altogether in having a special kind of absorbing root which sinks down into the bark until it reaches the wood of the "host" tree. The sap running up the tree is then tapped by this root, and goes to supply the mistletoe with water and salts in solution. It has, however, its own green leaves. Thrushes eat the berries of the mistletoe; they will be left upon a branch with the guano; as the latter dries up, the seed is drawn to the underside of the branch, and sticks in a crack 334 or crevice; it then sends the sinker-root mentioned above into the branch. Every year afterwards new mistletoe "roots" are formed which grow through the soft part of the bark and send down sinkers into the wood. Cases of Mistletoes forty years old have been recorded. The trees which they prefer are the Apple, and after that Black Poplar, though mistletoe may be found on Silver Fir, various Pines, and others. It is more difficult to get it to grow on the Oak than on any other tree. Indeed, only seven cases of mistletoe growing on oak have been recorded in this country.[145] It is quite a valuable crop in some places, and is sent in tons to the London market. There are many species of Mistletoe, and at least one kind attacks, and is parasitic upon, another species of Mistletoe. Most Mistletoes and Loranthus have their own green leaves, and only take from the plant to which they are attached sap and mineral salts. But in Chile there is a beautiful Loranthus that has practically no green leaves at all. Its blood-red flowers grow in dense masses upon the giant Cactus, which is common on the drier hills, and these are always mistaken for the Cactus's own flowers, which are quite different. These almost leafless Loranthus, and the curious Arceuthobium are more parasitic than ordinary mistletoes, for they obviously take other food material (probably sugar and albuminoids) from their "host." Another series of parasites or cannibals are quite common in Great Britain. One often sees in some meadow that the grasses are growing in a scanty and unhealthy manner; one then notices amongst them numbers of the Yellow Rattle or the Eyebright (which the Germans call Milk-thief). These 335 plants are not very remarkable in any way, but if one examines them closely one sees that the leaves and stems are more purplish-red than is at all usual with our ordinary flowering plants. But if you dig up some specimens very carefully, then the wickedness of the Yellow Rattle and Eyebright becomes apparent; every here and there upon their roots are little whitish swellings which are firmly attached to the roots of other plants (generally of grasses). These two robber plants send from these swellings minute sucker-roots which pierce into the grass-root and intercept the water which the grass has been absorbing for itself. They are therefore parasites, and indeed they may cause a considerable loss of forage in a meadow. A good many other British plants are root thieves. Besides these two, there are the Cow-wheat, Red Rattles, Toadflax, Broomrapes, and Toothwort. A curious point about them is that they differ amongst themselves in the degree in which they are dependent on the work of others. Some are able to grow quite well without any such extraneous help, but the Broomrape and Toothwort are entirely dependent on others' labours. They have extremely little chlorophyll and very small leaves, and are clearly parasites "pure and simple." There are about 180 species of Broomrape (Orobanche). All of them attack roots, and most confine their attentions to one particular flowering plant. Their colours are generally very striking and unusual. Our British species are reddish, flesh-coloured, or dirty white, but some of the foreign kinds are blue or violet, yellow, or yellowish to dark brown. Generally the seedling Broomrape worms its way down into the earth till its root-tip touches the root of its special favourite host, then the root of the Broomrape fixes 336 itself for life; its suckers grow into the host and absorb all the food material which it requires. Those kinds which attack Tobacco and Hemp are dangerous pests and do considerable damage. The Toothwort (Lathraea) is so called because its scales have a sort of resemblance to human teeth. With the curious superstition which prevailed in medieval times, it was supposed that the plant must be a remedy for toothache because it resembled teeth. Unfortunately this is not the case. It is, generally, quite like the Broomrape in its method of growth, but it sends out long thread-like branching roots with suckers on the ends, which become fastened on the Hazel roots. For several years the plant remains underground and forms very odd-looking, white, scaly branches. These scales are rolled back in such a way as to form peculiar and irregular cavities which open to the outside near the tip of the leaf. There is no doubt that animalcula of sorts get into these cavities and probably die there. In that case, their remains will form a useful supplement to the diet of the plant. The following remarks, however, taken from Kerner have been disputed by other botanists. Certain of the cells lining these cavities "appear to send out delicate filaments. "When small animals penetrate into the labyrinthine chambers of a Lathraea leaf and touch the organs just described, the protoplasmic filaments are protruded and lay themselves upon the intruders. They act as prehensile arms in holding the smaller prey, chiefly Infusoria, and impede the motion of larger animals so as to cut off their retreat. No special secretion has been observed to be exuded in the foliar chambers of Lathraea. But seeing that some time after the 337 creatures have entered the chambers, the only remains of them that one meets with are claws, legs, bristles, and little amorphous lumps, their sarcode-flesh and blood having vanished and left no trace, we must suppose that the absorption of nutriment from the dead prey here ensues...."[146] But strange as these Broomrapes and Toothworts may be, they are quite inconspicuous as compared with the gigantic parasites found in Sumatra and Java. In 1818, when Sir Stamford Raffles was making a tour in the interior of Sumatra, his party came across one of those extraordinary plants which have been called after him. Imagine a gigantic flower in shape resembling a very fleshy forget-me-not, but more than a yard across! The colour is a livid, fleshy tint, and the smell is like that of a charnel-house. This extraordinary Rafflesia Arnoldii is the biggest flower in the world. It has no proper stems or leaves, but consists merely of this huge flower-bud attached to the roots of Figs, etc., which traverse the ground in these forests. It is said to be only found in places frequented by elephants, which are supposed to carry its seeds on their feet. There are four other kinds known: all of them occur in Sumatra, Java, and other neighbouring islands. R. Padma for example, has a flower about eighteen inches across. The central part is a dirty blood-red, while the lobes have almost the colour of the human skin. This also has a "cadaverous smell, anything but pleasant." These weird Rafflesias seated on the roots "which wind about on the dark forest ground" have impressed every observer. Yet if one glances back, it is interesting to see how insensible are the transitional steps which lead from independent 338 life by the plant's own exertions to these last "pure parasites," which are entirely dependent on other plants for everything that they require. The only other flowering plant which we shall mention in this chapter is now fortunately very rare in Great Britain. This is the Dodder, Cuscuta. It belongs to the Convolvulus or Bindweed order, but is entirely different from the rest of the family. Some climbing plants do throttle or choke the trunks of young trees if they twine round them too closely, but the Dodder has an entirely special and peculiar way of supporting itself to the detriment of others. It has no roots, no leaves, and scarcely any green chlorophyll; the Dodder is just a twining, thread-like, yellowish stem which carries here and there small round clusters of little convolvulus-like flowers. Wherever the Dodder thread twines round a hop or other plant, it puts out small suckers which drive their way into the stem of the hop and take from it all the food which the Dodder requires. When well developed it forms dense yellowish tangles of intricately entwined threads, which may cover whole bushes and entirely destroy the supporting plants. The Flax, Clover, and Hop Dodders are perhaps the worst of them all. There are some rather interesting points in the history of the tiny dodder-seedling. It remains, quietly waiting, for about a month after most other plants have germinated. Then it begins to grow rapidly: its tip pierces the soil and becomes fixed in it; then the rest of the little thread-like seedling begins to curve round or revolve. If it touches a grass or even a nettle stem, it twines itself or coils round it, drives in its suckers, and, on the strength of the nourishment which it extracts, it goes on revolving or turning until it forms the dense tangled masses referred to. 339 Then an eruption of flowers appears, from which later on hundreds of tiny seeds are let loose which will become Dodders in their turn. The series of parasitic plants which have now been mentioned form a very interesting set. It must be pointed out that those which live merely on dead vegetable matter are "good" plants. They help on the quick and thorough employment of worn-out material. Nor can we say off-hand that other parasites are "bad." They do kill other plants and do them harm, but then, are they not like a cattle-breeder who sends his inferior cattle to the butcher, keeping only those which are the very best of their kind? Perhaps these plants, by destroying the weak and unhealthy kinds, are doing a great deal of good. Another interesting point about such parasites is that they are generally rare. They must be less common than their "host." Yet another is that they are all "degenerates." They show distinct traces of decay and bad development in their flowers and seed. That is also true in the case of parasitic animals. Whether they do good or harm to the world of plants is doubtful, but there is no doubt that they are doing harm to their own chances! 340 <div style="break-after:column;"></div>

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