Popular Science Monthly/Volume 30/March 1887/Animal-Plants and Plant-Animals
IF we examine the bright bow of Iris painted on the heavens by the sunbeams that break through the parting storm-clouds, no matter how closely we may scan it, we shall not be able to determine where the colors begin or end. As in this arch the blue gradually passes over into a green, and the green in turn changes insensibly into a yellow, even thus we find, in the countless forms in which Nature delights, the most delicate gradations, the most gradual transitions. Natura non facit saltus: this saying of Linné's is realized everywhere in the ever-changeful realm of life.
How difficult a matter it is to decide whether the lung-fish of Brazil and Senegambia belong to the amphibia or to the fishes, which in other instances are known to always breathe by their gills! In the rainless season of the year the swamps, the homes of these animals, dry out; they then coat themselves with a crust of earth, and are dependent on their lungs for every breath they draw. During the rest of the year they can use either these or their gills.
The close relation between fish and amphibia is established in yet another way by the Caudata, which retains its gills and does not lose them, as do its relatives, the frog and salamander. The olm of the Adelsberg grottoes also belongs to this class; it is an animal of a pale-red color, which spends its existence in subterranean darkness. Its eyes, as is also the case with other animals that live in constant darkness, are not developed, there being no possible use to which they could be put; they are very small, and lie beneath the skin.
A connecting link between the birds and the reptiles is found in the fossil archæopteryx brought to light in the slate-quarries at Solnhofen; the feathers denote a bird, the rest of the body is that of a reptile. The Ornithorhynchus paradoxus of Australia serves to connect the feathered tribe with the mammalia. It lives in seclusion in dreary regions on river-banks, and builds its subterranean home in such a manner that one of the two exits is always submerged by the stream. It has four feet, and a broad bill, with horn plates on the edges like that of the duck, and seeks its food like this fowl. At the foot of the male there is a spur corresponding to that of a rooster; between the toes are webs like those of water-fowl. It would hardly seem surprising to find this strange creature, in many respects so like the birds, propagating its kind by eggs; but it is a true mammal, and gives birth to live young.
The transition from the palms of the tropics to the palms of the north—the fir-trees—is made by the shining cycadees, whose leaves, as emblems of peace, are placed on tombs. The guetacea must also be regarded as intermediate between the lower and the higher orders of plants. To these belongs the curious "welwitschia" of Africa, the thickness of whose stem exceeds by three times the height. During its whole life—over a century in duration—it bears only two, but very large, leaves, fully two metres in length and one metre broad; it is well named "the wonderful."
At first sight the assertion may seem strange, that the dividing line between the animal and the vegetable kingdom is not definite, and that one may sometimes be in a quandary to know whether he is dealing with an animal or a plant. That the rose must be accounted a plant there can be no doubt; and that the gaudy butterfly, coyly hovering above it, must be classed with the animal kingdom, remains unquestioned. But it is by no means so easy a matter to determine the nature of that peculiar being which we find in damp moss. It is a slimy mass, but little colored; it moves slowly and in every direction, yet no feet are discernible. After a long dispute the botanists have had to accept into their realm these slime-fungi, for during a part of their existence they are distinctively plants, and propagate by spores.
Since the oldest times attempts have been made to find some features characteristic respectively of animals and of plants. But all of these criterions, one by one, have had to be abandoned. Finally, Haeckel, of Jena, severed the Gordian knot. He created an intermediate realm to which all is consigned that is not distinctively a plant or an animal. Now, however, the difficulty is only greater than it was before. Formerly the question was. Animal or vegetable kingdom? Now it has become, Animal, protista (for thus Haeckel named this new division), or vegetable kingdom?
This system of classification at least affords us a general view over those organisms which are, as it were, the connecting links between the vegetable and the animal world, between which, at first sight, there seems to be an impassable chasm.
The slime-fungi have before been alluded to; the class of fungi embraces yet other groups that, as animal-plants, call for some notice on our part. Above all must be named the bacteria; in 1853 these organisms were relegated to the vegetable kingdom. In the case of many bacteria, motion can be observed; some move quietly about, others slide and glide to and fro like snakes or eels. A few species are provided with special thread-like filaments for this purpose. Some bacteria, as well as many other kinds of organisms, can withstand—that is to say, survive—considerable heat. There are, for instance, the algæ in the waters of the Carlsbad Sprudel; they attain luxuriant growth at a temperature of 54°C. Other species of this kind live though exposed to the hot vapors (about 65°C.) of Ischia and Liparia. This is all the more remarkable as protoplasm, the albuminoid substance on which the phenomena of life depend, curdles at a much lower temperature.
A similar tenacity of life has been observed also in plants of a higher order. Wheat-kernels, for instance, if they have been previously well dried, lose the property of germinating only at 72°C, barley at 65°C.; if moist, however, they die at a temperature of about 50°C. The seeds of many leguminous plants can not survive a temperature of 35°C. Pouchet, however, has observed that seeds which were found in the unwashed wool of Brazil sheep resisted for four hours the action of boiling water. The hard seed-shells had prevented the entering of the water. Haberlandt in 1863 made experiments with the seeds of eighty-eight different kinds of cultivated plants, and found that some of them could, when in a perfectly dry condition, stand, for forty-eight hours, exposure to a temperature of 100°C.; in some instances, in fact, germination was hastened by the higher temperature. Nor is the power of germination always destroyed by intense cold. This is demonstrated by the fact that, of three hundred wheat-kernels which were left north by the Polaris in 1871, some sixty germinated in 1877.
Let us now turn our attention to a different group of organisms, before briefly referred to, and which formerly were regarded as belonging to the animal kingdom—some species of algæ.
In 1843 the botanist Unger, while examining certain green plantfibers under the microscope, suddenly noticed some sphere-like bodies dart out of these fibers and move to and fro in the water, kept in rapid motion through the aid of cilia.
This wonderful sight (for up to this time nothing like it had been observed) surprised him greatly, and he announced his discovery to his collaborators in an essay bearing the title, "The Plant in the Act of Transformation into an Animal."
To the algæ belong those minute organisms that sometimes give to water a bluish-green color, that redden snow, and that change ordinary rain into a rain of "blood." Ehrenberg states that the Red Sea takes its name from the algæ which it sometimes throws far up on its shores. Reports of "blood-rains" are not at all infrequent in the records of the past. Chinese history, written eleven hundred and fifty-four years before the Christian era, makes mention of such a phenomenon; the Bible writers speak of similar occurrences, and Livy also reports an event of this kind.
But only one group of these organisms, the diatoms, will receive our closer attention. They surpass the bacteria in size; still, a good microscope is needed to observe them. Whereas the bacteria present only few, and at that, simple forms, but colors of varied hue, the reverse is true of the diatom family. Their color, when they possess any, is a more or less dark brown or a green, but the delicacy and beauty of their forms is striking. Some look like minute gondolas, others resemble fans, or approach in form an S, a circle, or an ellipse. If a higher magnifying power be employed, most dainty linear tracings will be seen on their shells, for these beings are enveloped in shells which consist chiefly of silica.
Linné's expression, "Natura in minimis maxima" (with her smallest agents Nature accomplishes her greatest works), is especially borne out by the diatoms, for they have been active agents in the formation of the crust of our globe; rocks, ocean-beds, in short, entire geological formations, are the results of their labors. The polishing-slate of Bilin consists only of diatoms—one litre containing something like two billions of them. A considerable part of Berlin, the capital of the German Empire, is built upon a bed of diatoms, the uppermost layer of which is still alive.
Thus far we have noticed the power of locomotion—this prime characteristic of animal life—only in the lower orders of plants, the algæ and fungi. Might we not expect to meet with this also in plants of a higher order? Motion, perfectly free and unrestrained, we should here of course seek in vain, but many plants possess the power of moving some of their parts. In this connection we would recall the Mimosa, which, in response to the slightest touch, will immediately fold her leaflets. This same effect is also induced by cold and darkness.
The flowers of many plants are found in certain ways to be greatly dependent on temperature and on light. They open in the morning when the sun has reached a certain place in the heavens, and close again at a stated time at night.
Some plants can open their flowers or parts of them very quickly. For instance, the Martha of the tropics, on the approach of an insect, ejects its pollen suddenly, and then as quickly closes the entrance to the flower, and refuses the insect admission. Motion of a different nature is shown by the climbing plants that were so closely studied by Darwin.
At times one hears or reads of the wandering of plants. But how is it possible that firmly rooted plants should be capable of changing their position? And yet this is so. In most cases, it is true, the removals are made merely by the seeds and not by the plant as a whole. Sometimes, however, the whole plant starts out to travel; this is generally accomplished by the friendly aid of the wind. The world-famed Anastatica, the rose of Jericho, comes in for mention here. It has the peculiar property of spreading out its branches, that at other times are folded to a ball, whenever its roots are moistened by water. In its dreary home, the deserts surrounding the Red Sea, it is but slightly fastened in the loose sand. Without much trouble it is torn from its bed by the winds and borne to great distances.
Some species of algæ, which form green or yellowish-green masses on the surface of placid waters, are thrown on the land by inundations, and are kept back after the waters have subsided, and finally dry into a peculiar matted substance not unlike coarse packing-paper. This is taken up by a strong wind and carried away. These wandering masses, which some people have readily connected with superstitious conceptions, are called "meteor paper." The water-pest is another plant that spreads itself in the same manner; as far as can be ascertained, it was transplanted in 1835 from North America to Ireland, and from there to the European Continent.
The majority of plants, however, are spread by the aid of their seeds, which are covered with hair or a fine woolen fiber, and can thus be easily scattered about by the winds, just as some varieties of spiders, in spring and autumn time, clinging to a silken thread, intrust to the winds the choice of their future home.
Let us now turn to a group of plants which claim interest by being possessed of a faculty generally attributed to animals only. Not satisfied with the nourishment which the humidity of the soil and the atmosphere afford, they seek to obtain a kind of food which Nature has, strictly speaking, denied them. I mean the insect-eating plants.
The knowledge of the existence of these curious beings is not really of a recent date, but former investigations remained unheeded. Only after Darwin had made his researches were they recalled, and at once commanded the interest of naturalists to such a degree that, at present, there are known over three hundred plants that feed on insects. They belong to various families, and are found in all parts of the globe. But how can the firmly rooted plant capture and grasp the light-winged insect; how can it retain the same sufficiently long to let the digestive juices act upon it? Naturally, in many cases, the sticky substance which is secreted by the leaves is the active agent, as, for instance, one may observe small animals adhering to the resinous stem of the "flytrap." But many plants are provided with special organs for this purpose, and they are able to catch the most nimble of insects with ease and dispatch.
One of the best known of these insect-eating plants found here, as well as in Lapland and Scandinavia, is the Sun-dew (Drosera), discovered about a century ago. Another plant, the so-called Flytrap of Venus (Dionœa) of America, which was brought to England one hundred and twenty years ago, has received the name of Venus for the reason that, like the goddess of Beauty, it attracts and captivates everything that heedlessly approaches it. At the bottom of the plant the leaves cluster like a rosette; from the center of this arises the flower-stalk. The edge of the leaf, which is nearly circular, is overgrown with strong bristles, while its surface is covered with small glands, at either side of which are three long hairs. A fly approaches; carelessly it settles on the leaf, and perchance touches one of the six long hairs: suddenly the leaf folds, the bristles interlace, and the insect is caught. Oftentimes the whole tragedy takes but ten seconds. The sensitive hairs have performed their duty; now begins the work of the glands. These discharge a large quantity of a colorless acid slime—the digestive fluid, pepsin—and the closed leaf changes at once into a stomachic organ. After a lapse of eight or nine days the leaf reopens, the insect has disappeared, the prey has been consumed. The above-mentioned facts constitute the main features of the process of digestion, but in connection with it many questions arise. What happens, for instance, if a non-edible object irritate the hairs, perhaps a stone or a piece of wood? The leaf closes with the greatest possible swiftness, but soon discovers its mistake, and does not discharge the digestive juice; after a lapse of twenty-four hours it again unfolds, ready for another capture. This does away with the marks of distinction thus far generally accepted, namely, that "plants live, animals live and feel" (plantœ vivunt, animalia vivunt et sentiunt), for the Dionæa distinguishes quite readily, by taste and feeling, that which is digestible from that which is not. By experiment, it has been ascertained that nitrogenous nourishment is preferred by the Dionæa; hence every kind of meat (beef, pork, and veal, either raw, fried, or stewed) is digested by the plant; also albumen and cheese; the latter, however, causes disturbances during digestion, and the leaf easily ails. If nourishment be again offered to the same leaf, will it be able to digest a second time? Yes; but the process of digestion is much more tardy, and, if the plant outlive this exertion, it certainly perishes in making a third or fourth attempt. Too large a quantity of food will kill the plant immediately. This property, apparently so startling a one in plants—namely, their being capable of digesting animal food—loses in strangeness if we look about us more carefully in the vegetable kingdom. There we find not unfrequently this power of digesting nitrogenous—i.e., animal substances, or at least of changing them from a solid to a more soluble condition. For instance, the seeds of many plants store up food for the purpose of nourishing the young plant in the beginning of its existence. Albumen, a substance particularly rich in nitrogen, is first changed into soluble material by the young bud, and is then by degrees absorbed, or, in other words, digested. Other plants possess similar dissolving juices, but up to the present it has not been ascertained what advantages the plant derives from their possession.
Five grammes of the milk-juice of the fig, diluted with sixty grammes of water, will dissolve ten grammes of fibrin in twelve hours, and in a month's time can gradually digest as much as ninety grammes. In this respect the "melon-tree" (Carica papaya), a small tree of South America, has, above all others, claimed the attention of botanists. A few drops of the milk-juice, which fills all parts of this tree, are said to soften in a short time the meat of even old animals, and if we may credit the tales some travelers tell, it is sufficient to roll the meat up in these leaves for several hours to render it soft and palatable. From the milk-juice of the Carica there has been obtained a compact substance called "papaiine," three grammes of which will dissolve one hundred grammes of fibrin in two days, and it has furthermore been found that the action can be made a continuous one.
Let us now leave the domain of plants and enter into that of animals, so much more varied in number and form. We shall still fancy ourselves in the kingdom of flowers when we turn our attention to those variegated beings which cluster about the subaqueous rocks in wild profusion. There seem to be brilliant flower-calyxes of hyacinths, carnations, anemones, gently rocked to and fro by the water—calyxes which, even had they grown under the genial warmth of sunlight, could hardly bloom more beautifully. But should one try to gather a bouquet from among these magic flower-beds, he would scarcely have touched a bud, when a sharp, stinging pain, more disagreeable than the burning of the nettle, would be felt. Even the sea-rose defends itself, and stings; very quickly it sends forth from their resting-place filaments charged with a corrosive fluid, filaments that, until then, had remained spirally incased like a spring wound up and ready for use. And how enormous is the number of these weapons of defense; some individuals are capable of sending forth six thousand millions! In the last century the plant-like nature of these sea-flowers was so generally accepted that Réaumur, in the Academy of Sciences, did not disclose the name of Peysonnell, a physician of Marseilles, who first declared them to be animals, for fear of his being ridiculed. For what Aristotle, the founder of the descriptive natural sciences, had written more than two thousand years ago, had passed into oblivion.
And how much greater is the resemblance which is borne to plants by those little animals that build the immense coral reefs; which turn again into rock that which the solvent power of the waters had at one time extracted from the cliffs! Very early in the history of the world, these little builders entered into the thoughts of man. Mythology attributed their origin to plants, which were said to have been thus transformed, as is related in the following legend: When Perseus had released the beautiful Andromeda from the terrible monster, he placed the head of the Medusa, whose frightful aspect turned to stone everything that beheld it, on some plants which he had taken from the ocean. But lo! these plants were immediately turned to stone. The water-nymphs soon came to satisfy their curiosity, and to marvel at the wonder. Playfully they scattered the seeds of these stone-plants into the ocean, and behold, the corals were created!
Not unfrequently hidden coral reefs prove a source of great danger to navigation. Two hundred and fifty years ago only thirty coral islands had been located in the strait between New Holland and New Guinea; now they number over one hundred and fifty, and soon, perhaps, this channel will become impassable. But is it not probable that other forces, besides the growth of the corals, are here actively at work? One of the most changeable parts of the globe is the neighborhood of that wonderful island, Australia. Numerous are the islets which there slowly arise from beneath the waters; numerous those which gradually disappear. Darwin was the first to show how sure a proof of geological changes such coral reefs are. The polyps which build them die at a depth of thirty metres, and the contact with the atmosphere is fatal to them. Hence, very deep coral structures denote a sinking, those above the water, on the contrary, an upheaval of the earth's crust.
And as the Jura, a part of the Alps and the Carpathian Mountains, display marks of such animal structures, it is a proof that all those mountain-ranges have, in the past ages, arisen from the ocean. They must have risen from a warm ocean, warmer than the climate of those regions is to-day, for the tropics only are the home of the reef-building coral-polyps. And how enormously they multiply under favorable circumstances is shown by the barrier-reef, four hundred miles in length, near the northern shore of Australia. Between it and the mainland there is a channel, over six miles in width, the water of which is calm, and always affords to vessels a refuge from the wildest storms.
And when we turn our gaze on the fauna existing between the branches of the coral, we behold animated life; a world in itself is spread before us; here dwell most of the various inhabitants of the sea—snails, shells, and sea-urchins, fishes and crabs of the queerest shapes. Here in the domain of color, where everything seems brilliantly attired, they are less easily discovered by their enemies than in the ocean. In fact, one can often observe that the exterior of animals is in accordance with their surroundings. The inhabitants of the desert have a sand-like color; those of the polar regions are of light shade; some caterpillars resemble the twig of a tree; some butterflies look like dried leaves; and a grasshopper has, on account of the shape of its body, received the name of "wandering leaf."
But the beautiful aspect presented by a branch of coral, when under water, immediately vanishes when it is removed from its native element, as the many little arms are then contracted. The skeletons of various species are, however, much sought for as ornaments, above all the black coral of India, which is considered a talisman. Next in value ranks the red coral, found near Algiers, and third in rank comes the white.
Another kind of plant-animals, which build structures like those of the coral, only not so large, not so hard, nor so lasting, are the sponges, sea-animals in the strictest sense of the term. The eastern part of the Mediterranean, and the Red Sea particularly, abound in valuable sponge-beds, on rocky soil. Numerous vessels arrive there every summer to collect the crop. Recently the cultivation of artificial sponge-plantations has been tried by taking a piece of fresh sponge, which still contained the slimy bodies of the sponge-animals, and planting the same in a favorable spot. The experiment succeeded admirably.
It seems easy and natural enough to turn our attention from the sponges to chalk. This very important writing-material is, as is well known, an accumulation of minute animal remains, or, more correctly speaking, of their calcareous shells. What large deposits they are capable of forming is shown by the chalk-cliffs of Rügen, by those of Great Britain, to which the island owes the name of "Albion" (white), and by those of Crete, from which the German word "Kreide" (chalk) is derived.
The chalk-cliffs arose from the ocean, but their later upheaval is due to volcanic eruption. The minute animals, which form the masses of chalk, are of various shapes; some resemble the houses of snails, some the cone of a pine, others again are staff-like.
The largest of the existing three hundred kinds have been known since the oldest of times, for they were found in the stones used by the builders of the Pyramids. Their incasement is greatly perforated, and from their pores they send forth numerous fine, slimy feet, which constantly fluctuate to and fro. By adhering closely to one another they cover their food-supply, and then gradually assimilate the same.
As the aurora borealis flashes through the darkness of the polar region, the nights in the tropics are made light by a curious, brilliant phenomenon: particularly bright sparks flash out in the ocean, at places where the waves break over rocky cliffs. Over one hundred kinds of animals may co-operate in producing this magic effect. Among these are the Salpœ, the life-history of which Chamisso learned on his voyage around the world. He was the first to prove that the Salpœ which cling together in chains do not vary at all from those swimming about singly. Other agents of a phosphorescent sea are the Medusœ (sea-nettles)—many-colored animals, possessing the most weird of forms. Some kinds have the shape of a bell; long filaments hang down from the edge, and in the center they have long arms to capture and paralyze their prey; in this they are aided by a number of those nettle-like organs mentioned in connection with the polyps.
Occasionally these queer creatures become visible on the surface, in masses several miles in extent. The material of which the body is composed seems to be chiefly water, as a medusa, about twenty pounds in weight, yielded when dried only thirty grammes of gelatinous flakes.
After the ominous sea-serpent, one of the most interesting of the beings which inhabit the mysterious depths of the ocean is Huxley's Bathybius, made of nothing but shapeless, motionless slime. It has been supposed to be the common origin of the animal and the vegetable kingdom, from which all beings have gradually been developed. But lately science has become doubtful as to its true properties, and has begun to question its organic nature; many naturalists consider it nothing more than gelatinous gypsum. Another animal, somewhat of this nature, which several years ago crossed the path of science, like a flickering will-o'-the-wisp, is the Eozoön Canadensis; gradually it has become more and more deprived of the animal characteristics once ascribed to it, and has been again assigned to the inorganic world.
Many are the errors and pitfalls that mark the path along which ever-searching Science strives onward to truth; and yet even these, in their way, show a triumph gained by the divine power of the human mind over its human failings!—(Abstracted from Virchow and Holtzendorffer's "Sammlung gemeinverständlicher wissenschaftlicher Vorträge.")