Have plants Nerves: AUGUST STRINDBERG HAVE PLANTS NERVES P By AUGUST STRINDBERG - Office of publication: Rooms 2128-29-30-31, Park Row Building HAVE PLANTS NERVES > * “It is certain that multicellular plants and animals are de- scended from the Protista.” In this sentence Haeckel has had the courage to affirm that plants are descended from animals; and, as his demonstration appears to me irrefutable, I do not hesitate to lay down a posteriori the proposition that plants possess nerve-centres. The skin of the gastraea, low as it is, includes a rudiment- ary nervous tissue; zoöphytes (“ animal-plants”) have nerve- muscle-cells, and in echinoderms nerve-cells and muscle-cells are separated. People have wanted to put plants below the lower animals, on the ground of their incapacity to move from their place; but, if in truth the faculty of changing one’s place marked a higher round on the ladder of existence, one would have to consider birds and insects as supernumanly gifted, and put the zoöspores of algae in a higher grade than orchids. Let us call to mind the ascidian, which has been misused for so various purposes; it begins with a nomadic life and is endowed with a spinal cord; weary of sterile vagabondage, it finally fastens itself to the bottom of the sea, where it awaits its prey. When this occurs, it has lost its spinal cord, but not its nervous system; and its skin has been transformed into a sort of cellular tissue that is like the epidermis of plants. - | Originally printed in “Die Zukunft.” 3 4. HAVE PLANTS NERVES 2 Might the ascidian perhaps put us on the right track? Was it perhaps formerly a vertebrate, which, weary of com- bat, developed back into a tunicate, put forth a sort of root, and took on the cellular skin of plants? From what are plants descended, since they have preserved the manner of reproduction of mammals, and imitate their organs, male as well as female, to such a point that one might be taken for the other? Is the sea-wrack, whose epidermis bears gelatine and whose zoöspores possess voluntary motion, nearer to animals than the immovable beings that are covered with cellulose? Apparently not, though it is often very hard to make sure what in nature is progress and what is retrogression. If the snail becomes a mussel, as Haeckel has shown, that does in- deed mean a retrogression from the morphological standpoint, but, on the other hand, a useful progress for the mussel, which now, by its two shells hermetically closed and by its relative immobility, is much better protected than the snail was before. An insect that should settle on a plant to leave off its mobile life suddenly would without doubt be transformed into an aphis; it would gradually lose its finely-organized feelers and the wings that had now become useless, and its mouth would become an organ of suction, which would correspond to the root of a plant. If a branch of ivy that has wound about the trunk of a tree should begin to put forth adventitious roots, and these should practise functioning as organs of nutrition,-which perhaps” HAVE PLANTS NERVES 2 5 really takes place in ivy that climbs up on mortared walls, then the branch would finally be alienated little by little from the main root, and would become a parasite. I once tried the experiment with an ivy that was twining about a fir-tree with its adventitious roots; I cut it off, and the branch thus cut off lived twenty-two days. The dodder that fastens on nettles breaks off all relations with the earth as soon as it has taken root in its new host, — but at the same time it simplifies itself entirely. The mistletoe, which at first had to creep up trees, has in the sequel become completely a parasite. Its leaves are like cotyledons, and its manner of propagation approaches that of the cryptogams, since the stamens are in the parenchyma of the flower-leaves and the ovaries in that of the fruit-leaves. Nobody thinks of denying to plants the five animal func- tions,—to wit, nutrition, digestion, circulation, breathing, and propagation. The root is the plant’s stomach, and the hairs of the rootlets excrete, besides carbonic, acetic, and hydrochloric acids, several other organic acids. The fact that the root secretes hydrochloric acid gives it a striking re- semblance to the stomach of the higher animals. Has the root of the plant excretory glands which correspond to the liver and pancreas, and without which no digestion can take place? Botany answers: No. - In the lower animals the epithelial cells of the intestines ex- crete what we should call bile, and in insects the mucous - canals take the place of the liver. It seems very probable that roots have no liver; on the other 6 HAVE PLANTS NERVES : hand, it seems that the root-hairs, the digestion-sacs, and per- haps also the root-cap, possess the faculty of digestion, and that to such a degree that they can even digest stones. In short, the outer coat of the root, which is always glan- dular, excretes and absorbs like an intestine, and brings the half-prepared material into the central cylinder, in which the ascent begins, and which one might call a lacteal. This vessel terminates in the collar—in dicotyledons in the periphery of the stem—and, like the veins, transports the nutritious juice into the lungs or leaves, where what is called oxidation takes place. At least I will assume that the proc- ess in the leaf-lungs is an oxidation, though it might just as well be called an evaporation, an excretion of carbonic acid, water, ammonia, and nitrogen. So far all botanists are at one; but here their ways part. Some believe that the nutritious juice oxidized in the leaves descends through the plant to the special vessels; others, like Sachs and Van Tieghem, are of the opposite opinion. As the circulation thus far resembles perfectly the circula- tion of the blood in the higher animals, it is a very obvious suggestion to seek in plants too for arteries that spread the juices through the whole organism. - That it has not, however, hitherto been possible to clear up this point, comes from the fact that perhaps the nutrition takes place only periodically. Fruit-trees have two flows of sap, the one in spring and the other toward the end of summer. And the winter-sleep of plants that drop their leaves might very well be only a period of working up the sap. HAVE PLANTS NERVES 2 7 All this is still so little cleared up scientifically that one is compelled to go to school to farmers, gardeners, and apothe- caries in order to get in some measure a notion of how nature works. It is supposed to-day that in plants the circulation is regu- lated not by a heart, but by mechanical forces: as if the heart too were not mechanically active, like a pump! Fifty years ago it was believed that certain cells or vessels pos- sessed a movement of systole and diastole; to-day that is denied. A little-known author mentions in passing that the wind plays a special part in the life of plants. I cannot here discuss this in detail, but refer to the two flows of sap that I just now mentioned, and their remarkable chronological coincidence with the equinoctial storms of spring and autumn. Finally, as regards the reproduction of plants, it can be not only compared with that of the higher animals, but in a cer- tain sense even regarded as identical with it. - But, if one then asks how it is possible that such different - functions, each of which has its own organ, could be active without different centres of energy or organs of innervation, botany leaves us without an answer. Botany sticks to this, - that plants have no nerves, and their energy is everywhere in the protoplasm. Yet in reality this holds good only in the one-celled zoöphytes. Even the gastrula has under its skin a nervous tissue; and the hydra has sensory nerves which receive the impression, and motor nerves which execute the action. * See De Candolle’s “La Botanique.” 8 HAVE PLANTS NERVES 2 If we deny to plants consciousness and the senses, we cancel the brain; if we deny to them voluntary motion, we cancel the cerebellum and a certain part of the spinal cord. But, since we cannot deny to them either organized nutrition, digestion, circulation, or respiration, we must concede to them a part of the prolongation of the spinal cord, a part of the spinal cord, and the solar plexus, the sympathetic system of nerves. Darwin, it is well known, wanted to ascribe certain faculties to the cap that protects the tip of the root; nay, on this oc- casion he speaks directly of a brain. This little, tenderly- built organ seemed to him to be able to choose, feel, and dis- tinguish. He held it to be capable even of a conscious volun- tary motion. I do not know whether he is right; but I recom- mend the following to the consideration of botanists. I had for a long time sought with the microscope for the nerves of plants, and finally, in order to facilitate the dis- covery of the fibres invisible to the naked eye, I asked a - specialist in nerve-physiology “in connection with what mor- bid phenomena the nerves of animals become hypertrophied or ºtherwise abnormally developed?” His answer gave me the occasion for an experiment. I put a hyacinth-bulb in a vase so that the roots could not reach the surface of the water; this was to increase their activity, for they seek the water greedily. I often sprinkled the roots with the water, in which I had put starch and sugar. The strongest roots now pushed straight toward the water, without turning away from the light; but, as soon as they reached the water, I lowered the level, so that the roots, deceived in their hopes, were com- HAVE PLANTS NERVES : 9 pelled to continue their efforts. . . . When, after this, I opened the root-cap and treated it with osmic acid, it showed in black, under the microscope, nerve-elements that were com- pletely identical with the sympathetic nervous system of mam- mals. Osmic acid, it is well known, is the reagent for the nervous tissue of animals." - One day I laid vegetable tissues before a physician who was very proficient in the matter of tissues and of nerves in general, but little versed in botany. He was surprised to find that plant-cells multiplied by karyokinesis just like animal cells. He was astonished at meeting this wealth of tissue- types in organisms which stand so low in the scale, and of which he had read that under the microscope they showed only a wearisome uniformity. But, when I showed him the linear fibres of the pine, with their alveolar punctations, he noted their identity with the heart-muscles of mammals. He compared the sclerenchyma of the walnut-shell with the lamel- lar tissue of bone. The vessels with valves correspond to the veins and lymphatics. Neither were muscular fibres lacking; and he did not at all doubt the presence of air-tubes, or an- nular and spiral vessels, especially such as in insects open into the stomach. When I finally showed him the sieve- tubes, he confirmed my old assertion that they were so like the myelin-nerves of vertebrates that the one might be taken for the other. And yet, even when I informed him that these Any one who wishes to repeat the experiment may, if he is not a histolo- gist, compare with his preparation of the hyacinth root-cap Figure 97 of Klein’s “Histologie,” which represents a fascicle of the sympathetic nerve of a rabbit. 10 HAVE PLANTS NERVES 2 mysterious and much-debated vessels of plants had been by me colored violet with chloride of gold and black with osmi- um,-like the elements of the nerves of animals, -he dared not believe that plants had nerves. I appealed to a renowned botanist who had observed how the tubes made serpentine motions when the leaves of the mimosa were irritated. I as- sured him that an authority like Sachs had denied that these tubes transported the prepared sap into the leaves, so that they could be neither an aorta nor other arteries. I explained to him that they carried albuminates and fats, and that even fibrin had been found. All in vain! Plants had no nerves for him, for . . . they must not have any In order to bring more light into this matter, I would re- quest zoölogists to occupy themselves for a moment with the physiology of plants, and to examine these sieve-tubes, which resemble the myelin-nerves not only in the construction of the tubes with the fibre running in a sheath, but also in that they possess a ring which closes them, an annex-cell, and a motor plate, which in plants is called sieve plate. º These sieve-tubes—so it is asserted—transport albumi- nates, and serve only to spread the descending sap. But this - is not true, since every cell—and especially the nucleus—con- tains albuminous substances and fats. And even the rising sap contains albumen, as one can ascertain in spring if one cuts a grape-vine before the leaves are formed, or bleeds a birch-tree. Climbing and trailing plants have the largest sieve-tubes. Does this come from the fact that the beginning of independ- HAVE PLANTS NERVES : 11 ent motion demands motors? And are these tubes with their fibres therefore degenerated spinal cord? At the back of the eye there is a sieve plate through the middle of which the optic nerve goes. The outer layer con- tains a sieve-substance and a great number of oval nuclei. The brain contains, among other things, a substance that is called inosite, Cº Hº O'. One finds it again in certain plants, especially climbing plants. It has been supposed that plants were in general not sensi- tive, with some striking exceptions like the mimosa. In reality plants are sluggish, but very sensitive; only great patience is necessary to see their movements. The experiment that Claude Bernard tried with the mimosa, which he chloro- formed and thereby put into a condition of tetanus, is famous. As is well known, chloroform works first on the gray matter of the brain–consciousness is extinguished; then on the sensory nerves; the entire vegetative apparatus goes on performing its functions. Judge from this whether the mimosa does not possess other than purely vegetative functions. I would ad- vise people who are fond of comparing plants with hairs, nails, and feathers, which grow without feeling, to chloroform hairs, and see whether they then show any analogy with plants, -quite aside from the enormous difference that the hair does not propagate itself. It is hard to decide whether the nerves of plants possess ten- dencies to form ganglia, but it is not improbable. I can re- port facts that at least indicate something of that sort. The oxalis, as is well known, shows at the base of the pet- 12 HAVE PLANTS NERVES 2 iole a motor-organ for the movement of the leaves. I have found it in a specimen that had lived through the winter, which I had treated with hyposulphite of soda. My notes fur- nish this among other things: Oxalis, put into water that con- tained muriatic acid, did not close its leaves again when it was shut in by day in a dark closet; in water without the acid it always took place. When with the help of a lens I burned the midrib of a leaf, the leaf was paralyzed. Injured at any other place, the leaves closed again. One of the most sensitive plants is certainly the wild yel- low balsam, or touch-me-not, Impatiens moll-me-tangere. When I first took occasion to touch a ripe pod, and it sprang out of my fingers like an insect, scattering its grains round about, I thought I had to do with a living creature that meant to save itself by flight. How wisely arranged, said I to myself, that this plant which grows in the shade of trees can throw its seeds out to the sun! An older friend explained to me that inside it there existed a mechanism that executed this man- ceuvre; but he would not believe in any mechanician. Since then I have investigated the mechanism of the spring more particularly; it is remarkably well built. But the balsam understands other tricks too. Living under the trees of parks and woods, it stretches its golden-yellow flowers out to the sunlight during the day, and draws them back under its leaves for the night. As the leaf springs from the node of the jointed stem, I suspected a centre of energy in the interior of the node, and tried the following experiment: I cut stems from two different plants of Impatiens. I wounded the one in HAVE PLANTS NERVES 2 13 the node, the other in the internode, and then put both in water. The stem wounded in the node died at the end of ten minutes; the one wounded in the internode went on living. To this it has been inconsiderately objected that the stem wounded in the articulation loses its swelling by the loss of water and air. But there is no sense in this, for then it could not wither further than to the upper node. Furthermore, every gardener knows that one must not take a cutting off at the node, even though he cannot tell why.’ In order to test the point, to drive out the water and let the air press in, I directed the flame of a blowpipe (a) on the node of an Impatiens, -and the stem wilted and bent at once; (b) on the internode,-and the stem remained upright. Fur- thermore, the mimosa becomes stiff under the air-pump. Sachs is of opinion that this comes from the lack of oxygen. I assume a centre of innervation in the nodes; and a modern author has, without meaning to do it, given my assumption supports, –only weak supports, to be sure. Adolphe Prunet, in his dissertation on the nodes and inter- nodes in dicotyledons (Paris, 1891), has noted, among other things, that the nodes are richer in fats and albuminoids than the internodes; the substance, says he, is regarded as the fundamental substance of nerves. - If I add that Golgi's famous reagent, bichromate of potash and nitrate of silver, gave me nerve-reactions on the nodes of plants that I studied, it seems to me worth while that the question be more particularly attended to. * The same holds good of the collar of plants, which one cannot wound without the plant’s dying ; gardeners are very heedful of this. 14 HAVE PLANTS NERVES > The chief reason why the nerves of plants have hitherto been neither sought nor found is without doubt that neither bipolar nor multipolar ganglia, which are considered decisive tokens of nerve-elements, have been met with. But these ganglion-cells, resembling those of the higher animals, are found in the chlorophyll of algae. And, if one studies the diagram of the strychnos-fruit, one sees that every cell-nucleus is united with its neighbor by nerve-fibres. If one then seeks further for elements that are like the nerves and ganglia of crustaceans, gasteropods, and insects, one can find them in many places. I name only the root-cap; the collar; the folds of the leaves; the nodes of the stalk; the receptacle of the flower; the epidermis, especially the hairs, which might fairly be called the olfactory organ of the plant, and which are constructed like the hairs of the crab. As regards the sieve-tubes once more, I have lately learned that the like are also found in the crustacean Palaemon. To all who would study the nerves of plants I recommend the dissertation of B. de Nabias on the nerve-centres of gas- teropods and that of Alfred Binet on the nerve-centres of in- sects. The marvelous pictures in both works are very well adapted to throw light on this dark subject. Haeckel found that the ganglia of the crab contained cells which resembled the ganglia of the great sympathetic nerve of vertebrates. From this he derived the statement that the nerve-tubes con- tain a glutinous, transparent substance, and that the cells are in connection with the nerve-tubes. Nabias concedes that, even though in the details of the protoplasm one cannot com- HAVE PLANTS NERVES : 15 pare the vegetable cell with the animal cell, there yet exists an analogy on the whole, since they gave the same chemical and physical reactions. And in another place: that compara- tive histology shows that the dimensions of the nerve-element diminished in proportion as one ascended the scale of animal life. If there is a scale, then where do plants belong? Where?