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- Goethe's Morphology
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Despite separate bindings, its halves On Natural Science and On Morphology dissolve their apparently tidy division between inorganic and inorganic inquiry: the science of shape shifting that living beings elicit for Goethe extends past them to encompass many of life's purported opposites, while optics and meteorology infiltrate On Morphology 's method of observing life. See Holland's insightful comparison of Goethe's prose and elegiac versions of plant metamorphosis, 19— For a deft overview see Roe, and Jacob's classic study.
On periodical form around , see Lepenies's classic exposition 97— , and Koranyi — I am indebted to Kuhn's characteristically fine editorial notes for this and numerous hints to the essay, LA II, 10A, ss. Becker et al. See Breidbach's brief but illuminating analysis, — Meeker's study beautifully unfolds the French Enlightenment inflections of Lucretian figural materialism. Azzouni's and Blechschmidt's studies also thicken our account of Goethe's constructivist, rather than expressivist, poetics. Skip to Main Content. Search in: This Journal Anywhere.
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Pages Published online: 15 Jun See Bach on Schelver's specific contribution to Romantic Naturphilosophie. The description of the simple and elegant "ABC" model for the determination of floral organ identity Coen and Meyerowitz, and the discoveries of deep homology and conservation among the genes involved in the model, belonging to taxa that diverged some million years ago for reviews see Theissen ; Irish and Litt, , continue to accumulate at an accelerating pace, based on methodological refinements and extensions, in both speed and accuracy, that could hardly have been conceptualized little more than a decade ago.
Much of our fascination with the data of evodevotics arises from the sheer novelty of discovery in biological domains that had been previously and totally inaccessible. In this elegantly simple model that is nevertheless under constant reformulation, see figure 2 , based on genes with homeotic effects upon serially repeated structures arranged in systematic order with repetition in concentric whorls rather than linearly along a body axis , A genes operating alone determine the form of the outermost whorl of leaf-like sepals; A plus B genes regulate petals in the next whorl within; B plus C, the formation of the male organs, the stamens, and finally the most interior female carpels.
Functions D and E were added latter to adjust the model see figure 2. But, in his most fascinating intellectual move, Goethe proposes a complete account by grafting two additional principles onto the underlying notion of archetype: the progressive refinement of sap, and cycles of expansion and contraction. We may regard these principles as ad hoc or incorrect today, but the power of their conjunction with the archetypal idea can be appreciated with much profit, with some re-interpretation.
Goethe, faced with observations of both directionality and repeatability up the stem, recognized the need for both poles of this dichotomy. Up and down, heaven and hell, brain and psyche vs. Goethe, by no means immune the way of thinking in an age of Naturphilosophie, applied this major metaphorical apparatus of Western culture to plants as well, with gnarly roots and tubers as lowly objects of the ground, and fragrant, noble flowers as topmost parts, straining towards heaven.
Goethe viewed the growth of a plant as progressing towards refinement from cotyledon to flower. He explained this directionality by postulating that, moving up the stem, each successive leaf modification progressively "filters" an initially crude sap. Inflorescence cannot occur until these impurities have been removed. The cotyledons begin both with minimal organization and refinement, and with maximal "crudity" of sap: "We have found that the cotyledons, which are produced in the enclosed seed coat and are filled to the brim, as it were, with a very crude sap, are scarcely organized and developed at all, or at best roughly so" Goethe, , No.
Finally, the plant achieves its topmost goal: "While the cruder fluids are in this manner continually drained off and replaced by pure ones, the plant, step by step, achieves the status prescribed by nature. We see the leaves finally reach their fullest expansion and elaboration, and soon thereafter we become aware of a new aspect, apprising us that the epoch we have been studying has drawn to a close and that a second is approaching, the epoch of the flower" Goethe, , No.
Schilperoord, that take the statement literally. Terms such "crude sap" were used merely due to a total lack of any molecular knowledge at the time. In response to environmental and endogenous factors, this genetic status is directionally re-programmed in order to allow the flowering process to occur the sap is then directionally "purified".
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The florigen concept was more likely to prompt sarcastic grins than scientific inquiry e. Surprisingly enough, CO-driven floral stimulation can be graft-transmitted Ayre and Turgeon, As may be expected for a gene that controls development in response to transient stimuli, both mRNA and protein accumulate to only very low levels Suarez-Lopez et al. Accordingly, Arabidopsis co mutants are late-flowering and the overexpression of CO by transgenic Arabidopsis plants caused the expected early-flowering phenotype Putterill et al. More interesting, CO putative orthologs were found in many other plant species with diverse photoperiodic demands, including grasses and legumes Dornelas and Rodriguez , ; Hecht et al.
According to Goethe, the plant then grows towards a floral apotheosis, but too much nutriment delays the process of filtering sap, as material rushes in and more stem leaves must be produced for drainage. A decline in nutriment finally allows filtering to attain the upper hand, and the sap becomes sufficiently pure for inflorescence: "As long as cruder saps remain in the plant, all possible plant organs are compelled to become instruments for draining them off.
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If excessive nutriment forces its way in, the draining operation must be repeated again and again, rendering inflorescence almost impossible. If the plant is deprived of nourishment, this operation of nature is facilitated" Goethe, , No. And more revealing is the fact that the nutrient-regulated pathway and the CO-regulated pathway converge into the product of the LEAFY gene, which is a central integrator of the flowering pathways Ohto et al. In these taxa, the arrangement of reproductive organs follows a spiral phyllotaxy and not a whorled distribution and thus, an exception to the strict ABC model kind of gene expression is to be expected Kim et al.
Additionally, there is a smooth transition among floral organ identity as among petals and stamens, for example, are intermediate organs with petaloid identity bearing pollen sacs figure 3. This spiral arrangement of floral organs is genetically controlled and considered to be the retention of an ancestral character and reminiscent of gymnosperm strobili Baum, ; He et al. The molecular mechanism underlying phyllotaxy control is being unraveled and helical arrangement of floral organs can be induced in genetically manipulated Arabidopsis plants, which would normally produce whorled-arranged floral organs Hashimoto, He envisages three full cycles of contraction and expansion during plant ontogeny.
The interplay of these progressive and cyclical forces produces the full pattern of a general refinement up the stem, but impacted by discontinuities and transitions that express no directional pattern "contraction" of stem-leaves to sepals by bunching them together in a whorl, for example. The cotyledons begin in a retracted state.
The main leaves, and their substantial spacing on the stem, represent the first expansion. The bunching of leaves to form the sepals at the base of the flower marks the second contraction, and the subsequent elaboration of petals the second expansion. The reduction of archetypal leaf size to form pistils and stamens marks the third contraction, and the formation of fruit the last and most exuberant expansion. The contracted seed within the fruit then starts the cycle again in the next generation: "Whether the plant vegetates, blossoms, or bears fruit, it nevertheless is always the same organs with varying functions and with frequent changes in form, that fulfill the dictates of Nature.
The same organ which expanded on the stem as a leaf and assumed a highly diverse form, will contract in the calyx, expand again in the petal, contract in the reproductive organs, and expand for the last time as fruit" Goethe , No. Plant apical meristems are gradually patterned during embryogenesis Long and Barton, , culminating in the formation of a highly organized structure with overlapping functional domains for a review see Sharma et al.
The self-renewing stem cell niche is confined to the most apical, central portion of the meristem. Mitotic cell divisions in this region, which is called the central zone, causes displacement of daughter cells outward into the peripheral region figure 4.
These more rapidly dividing peripheral zone cells undergo differentiation and become incorporated into organ primordia on the meristem flanks. This model of meristem structure and functioning has been recently validated by in vivo analysis of meristem behavior Grandjean et al. Following germination, the shoot apical meristem generates an indeterminate number of leaf primordia, which may bear axillary shoot meristems.
During the switch to reproductive development, the vegetative meristems are commonly converted into indeterminate inflorescence meristems Ratcliffe et al. The product of inflorescence meristems are generally determined floral meristems, which in turn produce floral organs, which are, by definition, determinate structures.
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Growth and differentiation within the meristem structure must be coordinated to maintain meristem shape and produce normal organs. This implies that meristem cells exchange signals to coordinate their behavior, directing the two meristem functions: cell proliferation and organ initiation Traas and Vernoux, Only recently the molecular nature of the regulatory system controlling meristem behavior began to be unraveled Dornelas et al.
If the activity of floral meristem identity genes is reduced, flowers will develop with various shoot-like characteristics Ratcliffe et al. Thus, these observations are an exemplar case of a failure to perform the first Goethian meristem "contraction", or the conversion of indeterminate, spirally arranged inflorescence meristems into determinate, whorled floral meristems. The maintenance of the whorled state by the production of additional floral organs may be viewed as the second round of a Goethian meristem "expansion".
Besides being a C -function gene see the first section of this review , AG also limits proliferation of floral stem cells Lohman et al. While a central pool of stem cells replenishes the indeterminate shoot meristem, this pool is only transiently maintained in determinate floral meristems, which therefore stop producing new organs after the carpels have differentiated.
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Accordingly, in Arabidopsis ag mutants, organ formation does not terminate with the formation of fourth-whorl organs, but continues indeterminately. Contrastingly, the main shoot of Arabidopsis wuschel wus mutants terminates after producing only a few leaves Mayer et al. A molecular link thus exists between stem cell regulation and meristem patterning in plants figure 4. When the domains of either WUS or CLV3 expression are expanded or contracted, the meristem size and behavior in transgenic plants respond accordingly Schoof et al. In other terms, cycles of "expansion" and "contraction" of gene expression domains characterize the meristem behavior during all plant life cycle.
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Therefore, a final word must be said about Goethe's formalism: in classical formalist or structuralist theories, the strongest correlation unites a commitment to generative laws of form with an aversion to adaptationist explanation as the primary goal of morphology. Obviously, such ideas would make Darwin tremble into his grave. For Darwin, discontinuity originates by historical contingency following extinction of intermediate forms in a fully accessible and isotropic morphospace.