Paxton's Magazine of Botany (1849)
GOETHE'S ESSAY ON THE METAMORPHOSIS OF PLANTS.
(Translated from the German by EDWARD ORTGIES)
"Lo, he goeth by me, and I see him not;
he passeth on also, but I perceive him not."—Job, ix. 11.
"Voir venir les choses, est le meilleur moyen de les expliquer."—Turpin.
1. EVERY one who has studied even to but a little extent the vegetation of plants, will easily observe, that sometimes certain external parts will transform themselves, and, in a greater or less degree, pass into the shape of those parts nearest to them.
2. So we see, for example, that the single flower transforms itself into a double one, when, instead of stamens and anthers, there appear petals, either quite the same in shape and colour with the other petals, or still bearing evident marks of their origin.
3. If we observe that, in this manner, it is possible for a plant to make a step backwards, and to invert the order of vegetation, then we shall become more attentive to the regular way which nature goes, and we shall learn those laws of transformation by which nature produces one part through and out of the other, and forms the most diversified shapes merely by the modification of a single organ.
4. The secret affinity existing among the different external parts of plants, as leaves, calyx, corolla, and stamens, which develope themselves after and out of each other, has, in general, been noticed by naturalists long ago; and has been the subject of special attention, and this phenomenon, by which one and the same organ presents itself to our eye under so many modifications, has been called the Metamorphosis of Plants. (Morphology.)
5. This metamorphosis presents itself in three different ways: regular, irregular, and accidental.
6. We may just as well call the regular metamorphosis a progressive one; for it may be traced from the first seminal leaves gradually upwards to the last development of the fruit; by transferring one form into another as on an intellectual ladder, progressing towards the highest point of nature. It is this metamorphosis which I have attentively studied for several years, and to explain which I Undertake the present essay. We shall therefore, in the following order, consider the plant only so far as it is annual, and notice its progress from the seed onwards to its fructification, without interruption.
7. The irregular metamorphosis may be considered as retrograde; for as nature in the former case hurries on to its great destination, so here, in this case, it goes backwards one or more steps. There she produces flowers as by an irresistible propensity and with mighty efforts fits them out for fructification; here, on the contrary, nature seems enervated, and her powers feeble, and though perhaps agreeable to our eyes, still inwardly deprived of power and action. By the experience, with which this kind of metamorphosis furnishes us, we shall be enabled to discover what is secreted by the regular metamorphosis; we shall also see clearly here what we could suppose only before, and in this manner we are enabled sooner to attain our aim.
8. From that kind of metamorphosis, however, which as accidental originates in external causes, chiefly by insects, we shall turn our attention away, as it might induce us to leave the simple road we intend to follow, and to displace our aim. Perhaps we shall find occasion another time to speak of these monstrous excrescences, which are still kept in fixed limits.
9. I have ventured to give this present essay without reference to explanatory figures, which in many instances might be found necessary. I reserve to myself to add them in future, which may be done so much easier, as there is plenty of materials left to explain and complete this present small and merely preliminary essay. In that case I shall not be obliged to take such measured steps as now. I shall be able to add other analogous subjects and passages, taken from authors, partake of my views. Particularly, I shall not forget to make use of all the works of those contemporary authors who are the pride and honour of this noble science; it is to them that I deliver and dedicate these pages.
[This essay was first published in the year 1790; it was reprinted in 1831, but Goethe did not fulfill the promises given in the above paragraph. It is greatly to be regretted that this truly great man—great as a poet, philosopher, naturalist, and historian, equally excelling in most of the different branches of science and literature—was prevented from bestowing more time and attention to morphology in his latter years. Finding himself unable to carry out his former intentions, and distracted by other literary and scientific pursuits, which completely occupied his time and thoughts, he added no original matter in the second edition, excepting a very interesting relation of his early life and botanical studies, in order to explain how he was led by degrees to conceive first the idea of a metamorphosis, and how he followed it out. And then he gives a compilation of passages from other authors, to show the influence and development of his original ideas by other scientific botanists. Note of the Translator.]
I. Of the Cotyledons.
10. As we are determined to observe the gradual development of vegetable growth, we have to direct our attention to the plant in that very moment that it bursts forth from the seed. In this period we may correctly and easily distinguish all its proper parts. It leaves its envelopes more or less behind in the ground; of these we shall take no further notice for the present. As soon as the radicle has taken hold in the ground, it pushes on and exposes to light the first organs of growth, which have been present already in the seed.
11. These first organs are known as Cotyledons, or seminal leaves.
12. They often appear deformed, as if filled with a raw matter, swelling out just as much in thickness as in breadth; their vessels are hardly distinguishable from the mass of the whole; they have little resemblance to a true leaf, and we might feel inclined to consider them as organs quite distinct from seed leaves.
13. In many plants, however, they approach nearer to the shape of leaves; they become more flat, and, exposed to light and air, assume the green colour to a greater degree; their vessels become more distinct, and begin to resemble the ribs of leaves.
14. Lastly, they appear to us as real leaves; their vessels are capable of the most delicate development; their resemblance with the succeeding leaves not allowing us to take them for proper organs, we call them, therefore, the first leaves of the stem.
15. It is impossible to imagine a leaf without a node, and a node without a bud (gem), so we may come to the conclusion, that the point where the cotyledons join must be the first true budding point of a plant. This opinion is justified by plants which send forth branches immediately out of the axillae of the cotyledons, as Vicia, Faba, &c.
16. The cotyledons are mostly double and opposite, and this causes us to make an observation which will as we proceed, appear of still greater importance. These leaves of the first bud are placed opposite, even when the succeeding leaves of the stem will be alternate. Here, therefore, appears a contraction and connexion of parts, which afterwards are standing aloof and separated. Still more curious it is when the cotyledons appear as many small leaves, collected around an axis, from where the stem rise, bearing the succeeding leaves solitary and alternate around itself; which case may be closely examined in the Coniferae. Here we see the cotyledons form a sort of calyx, and we shall in future have to remember the present case when we shall find other analogous phenomena.
17. Plants, which germinate with one seminal leaf only (Monocotyledones), we pass unnoticed for the present.
18. But we have to observe that even such cotyledons as approach nearest to the formation of leaves, if compared with them, will always be found of less perfect development. Particularly their margin is more simple, and presents few traces of incisions, as their surface is void of hair or other proper vessels of perfect leaves.
II. Development of the Cauline Leaves from Node to Node.
19. We may now closely watch the successive development of the leaves, as the gradually progressing actions of nature are now open before our eyes. Some few of the leaves have been present already in the seed-corn, folded up between the cotyledons, and in this state are called the plumule (gemmule, or primordial leaves). Their shape, if compared with the cotyledons and succeeding leaves, is different in different plants; but still, in general, they differ from the cotyledons in being flat, tender, and, in short, more like true leaves, of a green colour, with a bud at their base; so that their affinity with the other leaves is no more to be doubted: generally they are inferior to true leaves, by not having their margin so completely developed.
20. Meanwhile the ulterior development goes on from node to node throughout the whole leaf, elongating the central rib and spreading out side ribs, more or less inclining towards the sides. The different relations of the ribs towards each other are the principal cause of those many varieties of shape in leaves. Now the leaves may appear crenate, deeply incised, or composed of several smaller leaves, in which case they seem to form a perfect little twig. The Date Palm furnishes us with a striking example of the progressive modification from the most simple form to the most complicated. After several succeeding leaves, integral and simple, the middle rib begins to push on and elongate, the fan-shaped simple leaf is torn, separated into many leaflets, and another highly complicated twig-like leaf is developed.
21. In the same degree, that the leaf becomes more developed, the leaf-stalk developes itself, either as an immediate part of the leaf, or as a distinct organ, which afterwards may be easily separated from the leaf.
22. That this proper leaf-stalk (petiole) has a great inclination to assume the shape of the leaf, we may see in different plants, as in the Orange for example; and its organisation will give occasion to some observations, which we shall pass by for the present.
23. At the same time we shall not yet take any notice of the stipules; we only remark here, that if they form part of the petiole, they will likewise in the most remarkable manner be transformed with the metamorphosis of the leaf stalk.
24. As the leaves derive their principal food from the sap of the stem, more or less watery and undigested, so they derive their greater development and refinement from light and air. When we see the cotyledons produced in the seed corn not at all or very incompletely organised and developed, and as if filled with raw and undigested sap, so we shall see the leaves of aquatic plants, which grow under the surface of water, not so perfectly organised as those exposed to the free air. Plants will even produce smoother and less organised leaves in confined, low, and moist situations, which, if removed to more exposed places, will become rough, hairy, and altogether of a finer organisation.
25. In the same manner, we find the anastomose of the vessels which produce the cellular tissue of a leaf, by springing from the ribs and trying to meet at their extremities, if not solely produced by the influence of rarefied gases, still greatly assisted by them. If leaves of plants growing under water assume the shape of filaments, of become ramified like antlers, we feel inclined to ascribe this formation to the absence of a perfect anastomose. The growth of the Ranunculus aquatilis illustrates this theory in an evident manner; those leaves which are produced under water consist of thread-like ribs only, but those produced above water have their ribs filled with the cellular tissue, combining them into one integral leaf, by the perfect action of the anastomose. We find even leaves where this action has been in operation only partly, that in consequence they are partly integral and partly filiform, thus clearly showing the transition.
26. Experience has taught us that leaves consume different gases, which enter into combination with their internal fluids, and there remains no doubt that this digested sap returns to the stem, and forms the chief food of the bud, in or near the axil of the leaf. Scientific men have analysed these gases, contained in leaves and stems, and have perfectly ascertained this fact.
27. We observe in some plants that one node comes out of another. With the Gramineae, where the haulm is closed at every node, it is quite evident. Not so in other plants, which are either quite hollow in the centre, or filled with pith, or, rather, with medullary tissue. As it has been doubted lately whether pith deserves the highest rank, in consequence of being supposed the principal seat and cause of growth and vitality, and as it is now asserted, and I think with good reasons, too, that the internal side of the second bark, called the liber, is in reality this seat of vitality, so we shall now sooner become convinced that a node, deriving its food from the lower one, will receive this fluid in a more purified and filtered state, at the same time deriving benefit from the lower leaves, and that it therefore will be enabled to develope itself to greater perfection in nourishing its leaves and buds with a more digested sap.
28. In this manner, as the raw and unprepared sap becomes digested and finer, the plant itself will gradually become more perfectly developed, till it arrives at the limits fixed by nature. We now see the leaves in their greatest perfection, and shall soon observe a new phenomenon, which implies that the period we observed till then is at an end, and a second one is approaching—the period of flowering.
III. Transition to the Flowering period.
29. This transition will arrive quicker or slower. In the last case we generally observe that the leaves begin to contract again, specially to lose all their different incisions of the margin, but expanding more or less towards their base, where they are connected with the stem; at the same time we observe the space from one node to another becoming longer, or the stem at least to become much thinner than before.
30. It has been observed, that abundant food hinders the flowering period, but, on the contrary, that a less plentiful, even scarce supply, will accelerate it. Hereby we see still clearer the action of the leaves, of which we treated in the preceding paragraphs. So long as there are raw fluids left to digest, so long the plant will continue to produce organs fit for digesting this food. If there is a surplus supply of food, this operation will necessarily be carried on, and a flowering period becomes almost impossible. In withdrawing food, therefore, we assist and accelerate nature; the organs become refined, the action of the digested sap is more powerful, the transformation of the organs becomes possible, and usually goes on without interruption.
IV. Formation of the Calyx.
31. Sometimes this transformation proceeds with great rapidity, and in this case the stem, from the base of the last perfect leaf, all at once shoots up, elongated and thinner, and collects at its extremity several leaves around its axis.
32. That the leaves of the calyx (sepals) are really quite the same organs which, until now, appeared to us stem leaves. They now, however, often assume a very different character, by being placed around a common centre; this may be proved in the most evident manner.
33. We have in the Cotyledons already observed a resembling action of nature, in seeing several leaves or even several buds collected around a common axis. Many species of Coniferae produce in germinating, a radiating circle of unmistakable leaves, which, contrary to the general formation of Cotyledons, are already greatly developed; and we see in the very infancy of these plants the first slight traces of that power of nature, by which at a more mature age the inflorescence is produced.
34. Moreover, we find in several plants the stem leaves, without being greatly altered, brought together underneath the corolla, forming a sort of calyx. As they still bear their perfect shape, it will suffice to refer to our eyesight, and to the botanical term of "floral leaves" (bracts), which has been given to them.
35. With deeper attention we have to study the case already mentioned, where the transition to the flowering period proceeds slowly; the cauline leaves transforming and contracting by degrees, and as if gently insinuating themselves into the calyx; this we may readily observe in the calyx of the Sunflower, Calendula, and many others.
36. This power of nature, which collects several leaves around a common centre, shows us a still more intimate combination, and renders this collection of leaves still more indiscernible, by uniting them either partly or wholly. These leaves, lying so closely together, and touching each other in their infant state, become more or less united by anastomose through the influence of the greatly purified sap now contained in the plant, and thus form the campanulate, or so-called monosepalous calyx; but the incisions, more or less deep, show us still its compound origin. We may convince ourselves of this fact, by comparing a number of deeply-incised monosepalous calyxes with polysepalous ones; specially in watching the formation of the calyx in Synantherae. So we shall see that the calyx of Calendula officinalis, which in botanical terms is described as simple and multipartite, consists, in fact, of several united leaves, adding contracted cauline leaves, which, as it were, stole themselves into the formation of the calyx, as we have mentioned before.
37. In many plants the number and shape in which the leaves of the calyx (sepals), whether separate or compound, are placed around their axis, is constant, as well as the number of the following parts. In other plants the number and shape of these parts is not so constant; but even this irregularity could not escape the keen eyes of observant botanists, and they have succeeded in bringing these deviations of nature into a narrower compass, by a more careful inquiry into their character.
38. In this manner, therefore, nature forms the calyx, by producing several leaves, and consequently several buds, around a common centre, mostly of a certain fixed number and order, which otherwise would have been produced in succession, and at some distance from each other. If the flowering period had been hindered by a superfluous supply of nourishment, these leaves (sepals) would have remained separate, and have continued in their original shape. Therefore nature does not produce a new organ in the calyx, but merely combines and modifies those organs which we have known as leaves, and thereby approaches one step nearer to the great end of existence.
V. Formation of the Corolla.
39. We have seen that the calyx is developed by rarified sap, which by-and-by is produced in the plant, and that the calyx now in its turn becomes an organ for a still greater purification. This will become credible if we only consider its action as merely mechanical. For how very fine and fit for the most delicate filtration ought these vessels to become, which, as explained above, are contracted and drawn together almost to the highest degree possible.
40. The transition of the calyx into the corolla we may observe in more than one case, for though in general the colour of the calyx remains green, like the leaves, still it often changes colour in some parts, either at the points, margin, back, or inside, the outside still retaining the green colour; and we find this coloration always combined with a certain degree of refinement. In this manner an ambiguous calyx is often formed, which might with the same right be taken for a corolla.
41. After having observed that upwards from the Cotyledons a great expansion and development of the leaves takes place, chiefly at their circumference, and from thence to the calyx, a contraction of the leaves, we may now observe another expansion in the formation of the corolla. The leaves of the corolla (petals) are generally much larger than those of the calyx (sepals), and it may be shown that, as the organs in the calyx become contracted, they will expand in the corolla, refined to a great degree by the influence of purer sap, filtered by the calyx, as new and quite different organs. Their tender organisation, their colour and odour, would render their origin quite indiscernible, if we could not watch and surprise nature in several extraordinary cases.
42. So we find sometimes inside of the calyx of the Pink a second calyx, partly green, indicating the tendence to a monosepalous and partite calyx, partly lacerated, and at its points and margin bearing the rudiments of delicate and coloured petals, thus in this instance clearly showing the affinity of calyx and corolla.
43. The affinity of the corolla with the leaves shows itself in several ways; for the leaves of several plants become more or less coloured long before they approach to the state of inflorescence; others become completely coloured near the flowers.
44. Sometimes nature seems to omit the calyx only forming the corolla, and in this instance we have likewise the opportunity to observe the transmutation of leaves to petals. So we find sometimes a Tulip-leaf become a petal of perfect shape and colour. It is still more curious, if, as it sometimes happens, such a leaf appears half green, connected with and belonging to the stalk, at the same time that the other half is coloured and raised with the corolla (Perianthium), so that the leaf is torn in two parts.
45. It is a very probable opinion, according to which the colour and odour of the petals is accounted for by the presence of the male seed (pollen) in the flower. This seed, contained in the petals, is probably not yet elaborated enough, but combined and diluted with other saps; and the beautiful shades of colour lead us to think that the matter contained in the petals has attained a great degree of purity, but not the greatest, in which case they would appear white and colourless.
VI. Formation of the Stamens.
46. This will become still more probable, if we consider the great affinity of petals with stamens. If the affinity of all the other parts among each other was equally striking, so generally observed, and placed beyond all doubts, this present essay would then appear quite unnecessary.
47. In some cases nature shows us this transition quite regularly, as, for example, in the Canna, and several other plants of this family. A genuine and little changed petal contracts at its upper part, where it bears an anther, and forms in this instance a true filament.
48. We may best observe this transition in all its stages in flowers inclining to become double. In several kinds of Roses we find in the inner circle of the complete petals others which are contracted, either in the middle or on the sides. This contraction is caused by a small wart, which approaches more or less to a perfect anther, and in the same degree the petal will resume the more simple form of a filament. In some flowers of the double Poppy we find perfectly developed anthers resting on little changed petals of the very double corolla; in others the petals are more or less contracted by anther-like warts.
49. If all the stamens become transformed into petals, the flower will become sterile; but if there are some stamens left, the fecundation may take place.
50. And so we see that a stamen is formed when those organs which we saw expanding as petals, become again contracted, and at the same time much finer than before. The above-mentioned observation finds here again its confirmation, and this alternate action of contraction and expansion, by which nature proceeds to her aim, will more and more claim our attention.
VII. Of the Nectaries.
51. Quick as the transition of petals into stamens may be in many plants, we still shall have to observe that nature cannot always achieve this at a single step. She very often produces intermediate organs, which in shape and function approach nearer to one part or the other, and though these formations are greatly varied, they still may be collected under one definition, as forming "slow transitions of the petals into stamens."
52. Most of those differently formed organs which Linnaeus termed nectaries, may be comprehended under this definition; and we find here again occasion to admire the great acuteness and penetration of this extraordinary man, who, without being able to give a satisfactory explanation of these organs, relied on a mere presentiment in venturing to give one collective name to all these apparently heterogeneous organs.
58. Several petals show us their affinity with stamens, by bearing, without being visibly altered in their shape, glandular bodies, which exude a honey-like fluid. That this fluid appears to be an indigested, not quite elaborated fecundating fluid, we might feel inclined to think, from the reasons already mentioned; and this supposition will become much more probable by other reasons, which will be found in the following paragraphs.
54. Afterwards, we find the so-called nectaries of a determined and proper character, and in that case they approach in their formation sometimes to petals, sometimes to stamens.
55. We feel induced from the above reasons to count the paracorolla likewise with the nectaries. For, as the formation of the petals is brought about by an expansion, the paracorolla will, like the stamens, be formed by contraction. So we find inside of a perfectly developed corolla, a small and contracted paracorolla in Narcissus, Nerium, Agrostemma, and others.
56. We see in different genera of plants other changes in the petals, which are still more curious and striking. We observe in different flowers, at the base of their petals, a small cavity, filled with honey-like fluid. This cavity often becomes deeper in several plants, and produces on the back of the petals a spur or horn-like elongation, at the same time the whole petal becomes more or less modified. We may observe this in several species and varieties of Aquilegia.
57. We find this organ transformed to the greatest degree in Aconitum and Nigella damascena, but with a little attention we shall be able to recognise its affinity with petals. Specially in Nigella it easily resumes the shape of a petal, and by this transformation of nectaries to petals the flower becomes double. The resemblance of the nectary with the helm-like petal, which covers it in Aconitum, will soon be found out after careful examination.
58. After having explained that nectaries are gradual transitions of petals into stamens, we may now have opportunity to make some observations on irregular flowers. So we might, for example, describe the five external petals of Melianthus as genuine petals, and the five internal ones as a paracorolla, consisting of six nectaries, of which the upper one approaches nearest to the form of petals, and the lower one, already taken to be a nectary, bearing the least resemblance. From the same motives we might take the carina of papilionaceous flowers for a nectary, as, inclosed by the other petals, it forms itself nearest to the shape of stamens, and is very far off the petal, like the formation of the so-called vexillum. In this manner we might easily explain the brush-like bodies attached to the point of the carina in some kinds of Polygala, and might form a clear idea of the destination of these parts.
59. It is scarcely necessary to mention here, that it is not our intention in making these observations, to bring into confusion what has been separated and classified by others, we only wish to better explain the various formations of different organs by these remarks.
VIII. Some more Observations on Stamens.
60. That the sexual organs of plants are, like the other parts, produced by spiral vessels, has been raised above all doubts by microscopical observations. We take herefrom an argument for the internal identity of the different organs of plants, which have hitherto appeared under greatly varied forms.
61. Now, if the spiral vessels lie in the centre of bundles of vascular vessels, enclosed by them, we may get a remote idea of their great power of contraction, considering the spiral vessels, which really appear to us as elastic springs, in their highest degree of force, when they will become predominant, and, accordingly, the expansion of the vascular vessels become subordinate.
62. The shortened fascicles of vascular vessels can now no longer spread out, to seek each other again, and, by the action of anastomose, to form a net-work; the cellular vessels, formerly forming the tissue, cannot develope themselves now; all the causes by which leaves, sepals, and petals, expanded in breadth, fall away here, and a weak and very simple filament is produced.
63. If we now admit that the same vessels, which we before saw elongate, spread out and rejoin, are at present in a condition of the highest contraction; if we see them deliver their now highly-finished fecundating dust (pollen), which supplies, by its activity, what the vessels that contained it have lost in extension; if this pollen, now entirely free, seeks the stigmas, which, by the same action of nature, are growing towards the anthers; if it adheres to them, communicating its influences; we feel not disinclined to call this a spiritual anastomose, and believe it, at least for a moment, to have brought the ideas of vegetation and reproduction nearer together.
64. The fine pollen produced in the anthers, appears to us as a kind of dust; but these grains of pollen are only the vessels, in which a very fine fluid is contained. We quite agree with those who are of opinion that this fluid is absorbed by the stigma, explaining fertilisation in this manner. This becomes the more probable, as some plants have no pollen, but only a mere moist matter.
65. This reminds us of the honey-like exudation of the nectaries, and its probable affinity with the elaborated fluid in the grains of pollen. Perhaps the nectaries are preparatory organs; perhaps their honey-like fluid is absorbed and perfectly digested and prepared by the stamens; an opinion which becomes more convincing as this exudation is no longer observed after fertilisation has taken place.
66. We must not forget here to observe, though briefly, that the stamens, as well as the anthers, are very often united in different ways and degrees, showing the most remarkable instances of the action of anastomose, already several times spoken of, and of the combination of parts, which were quite separated in their origin.
IX. Formation of the Style.
67. After having been trying to prove the internal identity of the different organs of plants, developing successively, and so greatly varying in their external formation, it may easily be supposed that it is now my intention to explain the structure of the style and stigma, in the same manner.
68. We firstly consider the style, separated from the fruit (ovary), as we often find it in nature. We may do this so much easier, as it shows itself quite distinct from the ovary under this form.
69. We shall remark here that the style stands on the same point of growth where we find the anthers. For we could observe that anthers are produced by a contraction; now the styles are mostly in the same case; and we find them, if not always of quite equal length with the stamens, only a little shorter or longer. In many cases the style looks like a stamen without an anther, and the affinity of their external formation is greater than in the other organs. As both of them are produced by spiral vessels, we see so much clearer that neither part forms proper organs; and if the close affinity between them becomes evident by this observation, we find that idea—to call fertilisation an anastomose —much more evident and appropriate.
70. We find very often the style composed of several united styles, and the parts of which it consists are hardly discernible, even at their points, where they are not always separated. This combination, the action of which we have already often observed, becomes here more possible than ever; it must even take place, because these tender parts, before their perfect development, lay so very closely together in the centre of the flower-bud, that they may unite themselves to the most intimate degree.