evolution into ecology? the strategy of warming's ecological plant geography

Evolution into Ecology? The Strategy of Warming's Ecological Plant Geography

WlLLIAM COLEMAN

Department of History of Science University of Wisconsin Madison, Wisconsin 53706

From an ecological point of view, probably the major feature of Darwin's account of natural selection is the critical shift of perspective that marked his work after 1856. Having discovered the intimate connection between population pressure and species multiplication or divergence, Darwin moved the emphasis of his argument toward biotic factors and away from abiotic factors in evolutionary change. There remains, however, a widespread pre- sumption that the Darwinian scheme was intrinsically ecological and that ecology, after prolonged gestation, was brought forth in the image of its perhaps inadvertent sire, Charles Darwin.

I too begin with Darwin, but only in order to define a problem domain; my principal subject is the ecological reasoning of the influential Danish botanist Eugenius Warming. My focus is the strategy of Warming's all-important assessment of what he in 1895-1896 began to call "ecological plant geography." In the course of the discussion I offer the suggestion that Darwin's formulation of natural selection diminished his influence on the development of concrete, empirical ecological inquiry.

Darwin's mature conception of natural selection appears to have been bought at a high price. Both the basic notion of descent with modification and the outlines of an explanatory mechanism of descent (namely, natural selection) were in Darwin's hands by 1840. But natural selection was not a static concept. From the outset D ~ used it to explain adaptation, the adjustment and continuing readjustment of plant and animal forms to a changing, abiofic environment. The late Dov Ospovat has shown us that Darwin long held the view that natural selection molded the biological species to changing environmental conditions, the latter in turn being caused by incessant climatic and geological changes. 1

1. Dov Ospovat, The Development of Darwin's Theory: Natural History, Natural Theology, and Natural Selection, 1838--1859 (Cambridge: Cambridge University Press, 1981), pp. 191--209.

Journal of the History of Biology, Vol. 19, No. 2 (Summer 1986), pp. 181-- 196. © 1986 by D. Reidel Publishing Company.

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The process of adaptation, like that of the evolutionary changes of which it was the critical moment, was very slow, and its product, yesterday's or today's species, could be viewed as being well-nigh perfectly adjusted to the varied conditions under which it lived.

Adaptation, however, was only one part of the evolutionary story, and a deceptive part at that. In 1856 Darwin found a solution to perhaps the decisive evolutionary problem -- divergence, the production of two or more new species from a preexisting single stock. Adaptation, when effective, tuned an old species to new conditions; divergence assured the production of multiple new species. Divergence was Darwin's answer to the pressing question of evolutionary innovation. What is ecologically noteworthy in this advance is that Darwin's eye and mind now largely abandoned the abiotic environment as an interesting (that is to say, participatory) feature of the evolutionary process. The ultimate Darwinian explanation, population pressure (a strictly biotic matter), came to dominate the argument. Population pressure spurred competition; organisms competed for a "place" in nature. "Place" to Darwin was a subtle technical term, denoting position within a plant or animal community and between communities. "Place" was a matter to be explored primarily, perhaps even exclusively, in terms of food supply and behavior related to dietary needs.

The implications of Darwin's new understanding of divergence are remarkable, not least for the history of ecology. 2 In the Darwinian scheme, both in 1859 and in the long aftermath of the Origin o f Species, the abiotic environment offered the background against which was played the central evolutionary event, speciation. It provided, however, only an abstract background; for speciation was the result of divergence, and divergence was the product of population pressure and the ensuing struggle for a place in nature, both understood to be predominantly biotic phenomena. Of course, Darwin and the Darwinians viewed the economy of nature as embracing not only the living species but also the totality of those non-living conditions -- soil factors, temperature, air, light, water - - amid which plants and animals go about their affairs. Furthermore, Darwin and his followers insisted

2. See Pascal Acot, "Darwin et l'6cologie," Rev. Hist. ScL, 36 (1983), 33--48. Another perspective is offered by Peter Vorzimmer, "Darwin's Ecology and Its Influence on His Theory," Isis, 56 (1965), 148--155.

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that organisms and local circumstances must, if a species is to exist and prosper, stand in close harmony with one another. Darwin, Wallace, and Weismann, to mention only enthusiastic selectionists, offered numerous instances of this critical reciprocal relationship. Nature was, in the celebrated expression at the close of the Origin of Species, an "entangled bank," clothed with plants and populated by a diversity of animals. 3 Plants, animals, and the inorganic world were gathered together in a complex web, the pattern of which at any given moment was the product of "the laws acting around us," a summary statement of the evolutionary process.

For the history of ecology this seemingly promising conclusion poses the central problem. Darwinians spoke of and analyzed the evolutionary process and product, but while they also observed and emphasized the importance of the ecological product, nature's entangled bank, they paid scant attention to the ecological process itself. The precise detail of how, for example, an individual or a community adjusted its economy to that of its rivals, or how adaptations were to be physiologically assayed and expressed, were fundamental ecological questions, yet they received close scrutiny in neither Darwin's large manuscript, Natural Selection (begun in 1856 and never completed), nor in its abstract, the Origin of Species.

As is well known, it was Ernst Haeckel who baptized the new science of ecology. In so doing, he showed himself to be aware of the distinction suggested by Ospovat's analysis. Haeckel wrote:

With regard to the character of the conditions of existence, these are for each separate species extremely complex and in most cases are quite insufficiently or even altogether unknown. Where earlier we spoke of the conditions of existence, we considered especially inorganic conditions, factors such as the influence of light, heat, moisture and inorganic nutrients. Far more important than these, however, and exerting a much more powerflfl influence on the transformation and adaptation of species are organic conditions of existence, that is, the mutual relations of organisms to one another . . . That the interactions between all neighboring organisms are extraordinarily important and that they exert far more influence on the change and

3. Charles Darwin, On the Origin of Species by Means of Natural Selection, 2nd ed. (London: John Murray, 1860), p. 490.

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adaptation of species than do the inorganic conditions of existence was first emphasized with due clarity by Darwin. Unfortunately, these very complicated relationships between organisms remain for the most part unknown, and this because we have so far failed to attend to the question. Here, in fact, there exists a huge and interesting as well as important area of future inquiry. Ecology or the theory of the economy of nature, this being a division of physiology and one which our textbooks have totally ignored, when seen from this perspective promises to reward us with splendid and surprising discoveries. 4

This was Haeckel's first use of the new term "ecology." Some- what later in the Generelle Morphologie he spoke more fully of the character and possibilities of the hopeful new science and re- opened the prospect of useful and important inquiry into the inorganic or abiotic conditions of existence, s This was not, however, the general tenor of his work, nor had it been prominent in Darwin's major evolutionary writings. Ospovat's assessment is more revealing on this account, for it demonstrates clearly how Darwin's consideration of evolutionary divergence led him to emphasize the evolutionary autonomy of population dynamics and find reason to deemphasize, even to reject, an active role in evolution for the abiotic environmental background. In so doing, Darwin broke with a long tradition and with his own roots.

Enough, however, of the much belabored Darwin. While his evolutionary hypothesis did stress the integral fabric of living and nonliving nature, it did not in Darwin's hands bring exacting inquiry into the character and action of the bonds that joined organism, community, and environment. That emphasis arose, not unexpectedly, in another quarter. The fact is that many important persons whom historians have regarded as founders of ecology were working in an environmentalist and in some cases explicitly Lamarckian framework. F. A. Forel, Carl Semper, S. A. Forbes, Karl M6bius, Julien Vesque, Eugenius Warming -- all agreed that local environmental conditions had a direct morphophysiological influence on plants and animals. Some held that the changes so produced might be perpetuated by inheritance, although this

4. Ernst Haeckel, Generelle Morphologie der Organismen (Berlin: Georg Reimer, 1866), II, 234, 236.

5. Ibid., pp. 286--289.

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remained a much disputed claim. Obviously this orientation need not entail neglect of the community dimensions of ecological or evolutionary events. It was M6bius, for example, who in 1877 introduced the notion of the biocenosis, and it was Warming who, more than any other biologist of the late nineteenth century, insisted on the community dimension of ecology and placed community phenomena intimately and inseparably within the highly varied abiotic framework.

Raised in the moorlands of western Denmark, Eugenius Warm- ing (1841-1924) received his botanical training in the field and in the laboratory. 6 His career began with observations in the tropical savanna of Brazil. He returned to Copenhagen, completed his doctorate in 1871, and served as docent in botany at the university until 1882. Between 1882 and 1886 he was professor of botany at the newly founded university in Stockholm. He once again returned to Copenhagen, where he was named to the chair in botany and became director of the botanical garden. He remained at his alma mater until his retirement in 1911, by which time he had become a leading figure in both Danish and European science.

Warming travelled widely. In addition to Brazil, he went to Bonn to study microscopical technique and later visited Greenland and Finmark, the Mediterranean, and again Latin America -- these journeys being intended more to explore plant life in its natural setting than to seek and describe new species. He was highly critical of taxonomic work done for its own sake. Warming was that rare naturalist, the enthusiastic and thoughtful field worker who was also comfortable and creative in the laboratory. He accepted the evolutionary hypothesis during the 1870s and redirected his microscopical research from descriptive study of plant development to examination of plant structure in relation to adaptation. He never ignored the community for the individual species, a lesson surely learned in Brazil and evident in subsequent investigations and in the definitive publication of his Brazilian findings. 7 How, he repeatedly asked, does the structure and

6. The essential biographical account is Carl Christensen, "Eug. Warming, I, U," in Den Dansk Botaniks Historie reed tilhorende Bibliografi (Copenhagen: H. Hagerup, 1924--1926), I, 617--665, 776--806; II, 367--399 (bibliography). See also several essays by different authors in Bot. Tidsskr., 39 (1927), 1--27; C. Ferdinandsen, "Eug. Warming in Memorium," Fid. Med. Dansk Naturhist. For., 78(1924), xv--xxix.

7. Eugenius Warming, Lagoa Santa: En Bidrag til den biologiske Plantegeo-

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physiological capability of a plant or a group of plants fit an organism or a community to a definite place in nature and -- this being the essential question -- what conclusions can we draw from such knowledge regarding the distribution of plants? Warming's answers gave doctrinal coherence to and helped delineate the fundamental problems of ecology.

He had been asking such questions throughout his career, but the orientation toward community problems became foremost only after his return to Copenhagen in 1886. He was especially concerned with the acute economic problems involved in agri- cultural development in Jutland, a solution to which involved the use of plants in controlling moving sand and the conversion of heath into tillable land. Warming was also a master of the botanical excursion undertaken for pedagogical purposes (hence a keen student of Danish regional floras and their conditions of existence) and an experienced observer of radically different plant communities (Brazil, Greenland, arctic and temperate Europe). Drawing on this experience. Warming between 1886 and 1891 formulated a new view of how plant distribution was to be studied, s He articulated his notions in lectures in Copenhagen in 1890-1891, then offered them to the scientific world at large in the Plantesamfund of 1895, his principal contribution to plant ecology. This work, in its 1896 German translation, Lehrbuch der 6kologischen Pflanzengeographie, was surely the most influential single publication in the early years of the science. 9 I take the Lehrbuch (or Ecological Plant Geography) for my text as I attempt to show how the orientation given by Warming's example

graft [Kgl. Danske Vidensk. Selsk. Skr., ser. 6, Nat. Sci. and math. CI., VI, 3] (Copenhagen: Bianco Lunos, 1892). On Warming's years in Brazil see Christensen, "Eug. Warming," pp. 619--623; he served there as secretary to the remarkable Danish expatriate-zoologist Peter Wilhelm Lund. For Lund's curious Brazilian career see George Gaylord Simpson, Discoverers of the Lost World: An Account of Some of Those Who Brought Back to Life South American Mammals Long Buried in the Abyss of Time (New Haven: Yale University Press, 1984), pp. 40--53.

8. August Mentz, "Warming som plantegeografisk Forsker,"Bot. Tidsskr., 39 (1927), 39--41.

9. Eugenius Warming, Plantesamfund: Grundtraek af den okologiske Plantegeografi (Copenhagen: P. G. Philipsen, 1895); idem, Lehrbuch der ~ikologischen Pflanzengeographie: Eine Einfiihrung in die Kenntniss der Pflanzenvereine, trans. Emil Knoblauch (Bedim Gebrfider Bomtraeger, 1896; 2nd ed., 1902).

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and admonition reasserted the dynamic relation between plant and environment and focused attention upon the ecological process, thus introducing a new way to conceptualize and, above all, to analyze Darwin's entangled bank.

Consider the following. In chapter 4 of Natural Selection and of the Origin o f Species Darwin provided a striking example of local ecological change. The enclosure and planting some twenty-five years earlier of a plot on the Staffordshire heath had led to dramatic floral and faunal changes. The new larch and fir forest had brought in its wake several other species of plants and many new insects (or so Darwin supposed), and had even allowed oaks to germinate on the previously treeless moor. These changes Darwin attributed, with perhaps some hyperbole, "to the intro- duction of a tree [and] to no other change whatever. ''1° Here is a fine example of the power of biotic forces, species impinging upon species, other possible participatory factors being dealt a sub- sidiary role or no role at all. Darwin saw here a model of that "wondrous battle prolonged over centuries" by which each species establishes or reasserts its rights. The "war of nature" was fought by species and they used reproductive power, including the all- important matter of survival, as their principal weapon.

Thirty years later Warming described a similar instance of what Darwin had called rotation, and what the Dane and we today call plant succession. In ancient times Jutland had been covered by oak forest; the present dominant vegetation is heather (Calluna) and stands of beech. Only scattered groves of oak are found. But Warming did more than offer a description. He attempted to articulate the causal factors behindthe changes leading from oak to heath, noting the role of light and shade due to changing forest cover, the effects of humus formation and especially chemical change and loss, species replacement among low-rising plants of the forest floor, the advance of soil consolidation, and the dis- appearance of earthworms. Biotic factors were not neglected: Jutland beech and oak competed directly with each other, with the latter emerging at a distinct disadvantage. The fate of the oak, however, appeared to have been especially determined by that

10. Charles Darwin's Natural Selection: Being the Second Part of His Big Species Book Written from 1856 to 1858, ed. R. C. Stauffer (Cambridge: Cambridge University Press, 1975), p. 197. Also Darwin, Origin of Species, p. 71.

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ultimate biotic factor, the human species and its economic activity. Warming showed now forest clearing for smelting and then agriculture had over a period of several thousand years tipped the ecological advantage to beech and then to moor, doubly destroy- ing the oaks, apparently the postglacial climax forest. Clearing had changed light and water relations, laid bare the sandy soil of Jutland, and exposed all plants (the original forest as well as later crops) to the desiccating winds from the North Sea. 11

The Darwinian and the ecological view of nature are evident from these examples. Darwin was well aware of the many factors that determine a species' place in nature but, consistent with his central purpose of establishing a plausible mechanism of species transformation based upon the overproduction of individuals and differential survival, he elected to give priority to biotic factors. Other possible ecological factors were not denied: they simply had no decisive role in the argument and received little independent examination. With Warming the case was very different. He could presuppose the fact of descent and contemplate a wide range of proposed evolutionary mechanisms; he could also build his inter- pretation on the numerous specialized biological studies which, under the stimulus of Darwinism, had been conceptually trans- formed -- as was much of plant and animal geography -- or literally invented -- as was the morphophysiological study of adaptive mechanisms.

What is striking about the strategy of Warming's Lehrbuch is that the author intended a quiet revolution in the study of plant geography and not simply a manifesto, fortified by example, of the ecological point of view. Botany after 1850 was in turmoil. With M. J. Schleiden leading the attack, a campaign was begun to render the study of plants "scientific." This implied an end to mere description and species mongering and cast serious doubt on the legitimacy of even sophisticated taxonomic work. Most important, Schleiden and his associates sought to rid their science of any reference to "purpose" or design, whether explained in traditional natural theological manner or reflecting one or another pattern or process invented by an idealistic philosophy run amok. 12 The

11. Warming, Lehrbuch, pp. 365--370. 12. See Eugene Cittadino. "Plant Adaptation and Natural Selection after

Darwin: Ecological Plant Physiology in the German Empire, 1880--1900" (Ph.D. Diss. University of Wisconsin, 1981), pp. 7--40; Karl Miigdefrau, Geschichte der

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remedy was laboratory and microscope, and the hero of the day surely Wilhelm Hofmeister. Laboratory and microscope brought vast rewards, perhaps the most exciting being the discoveries made between 1850 and 1880 of the extraordinary life cycles of many plants. But the laboratory could not answer all questions, and it offered little to help the ecologist understand how plants (or animals) found and secured their place in nature. Plant parts and processes existed in startling number, complexity, and subtlety, but the microscopist who disdained asking why they did so could not expect to comprehend their purpose. Darwin's influential reassertion of the descent hypothesis and, not least, the stern control that natural selection was presumed to exert, permitted once again the posing of the question of organic purpose, now rid of supernatural connotations and, under the operative term "adaptation," seemingly open to rigorous analysis.

Microscopy and anatomical work in general could, in fact, do much more than describe structure and unravel life cycles. By the 1880s a tradition had emerged that adopted the study of adaptation, including attention to microstructure (for example, fiber bundles, stomata, and leaf structure in general), as the primary task of the plant morphologist. This new study, led by Simon Schwendener in Berlin and brought to fulfillment by Ernst Stahl in Jena, seemed tocreate a way to look at the plant simultaneously as a functioning entity and as an evolutionary product. 13

Warming in his early years had been part of this development. Although not spurning taxonomic work altogether, he mastered the new techniques and made important contributions to microscopical plant anatomy and physiology. TM His general outlook, however, was corrosive of the basic objectives of taxonomy. It was important, he held, to get away from the long-standing view that a biologist's first order of business was to prepare an inventory of nature, however complete, subtle, or precise that catalog might be.

Botanik: Leben und Leistung grosser Forscher (Stuttgart: Gustav Fischer, 1973, pp. 161--175.The notion of purpose was central to nineteenth-century discussion of adaptation and posed numerous problems for those who ventured into such discourse. The context and character of the dilemma is delineated by Timothy Lenoir, The Strategy of Life: Teleology and Mechanics in Nineteenth-Century German Biology (Dordrecht: D. Reidel Publishing Co., 1982), pp. 195--280.

13. The most important study in this area is Cittadino, Plant Adaptation. 14. His principal contribution is "De l'ovule," Ann. Sci. Nat. Bot., 5 (1878),

177--266.

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He had hopes, too, that his work would replace descriptive plant geography.

Descriptive plant geography asked what plant is found where, an interesting question no doubt essential to further inquiry. Warming's complaint was that such descriptive work never did get to this other, more important inquiry, into adaptations and community structure and classification. Worse yet, the phytogeogra- pher confined himself largely to floristics. To be sure, the parts of the flower subserved the reproductive functions of the plant, a significant aspect of the plant economy and a critical matter for such long-term considerations as speciation and phylogeny. But floral parts were not the parts with which a plant or a species directly negotiated its survival in a given locality or amid com- peting plant communities. Of primary importance were the shape, structure, and number of leaves; root form and distribution; duration of life; and other such characteristics, These features, some discernible only with the microscope but others visible to the naked eye, expressed both the economy of the plant and the place of the plant in the general economy of nature. They spoke directly of interactions between plant and environment and between plant and plant. There were patterns, too, among these many adaptations -- fitting, for example, taxonomically distinct plants to similar environmental conditions and placing floristically alike plants in very different settings. Distribution and adaptation were inextri- cably bound to each other, and together they raised a host of new and significant questions. For Warming ecology was the science that needed to be invented to deal with these matters.

Because, he observed, "species are by no means evenly distributed over the areas they occupy but group themselves into communities of very varied physiognomy" or appearance, the new science must be capable of explaining the many peculiarities of distribution. Why, he asked, "do species join together to form definite communities? Why do these communities present a definite physiognomy?" Such reasoning led to a "much more difficult matter," the question of the "economy of plants, of the demands that plants make on the environment [Lebensbedingun- gen]. How do plants make use of surrounding conditions and how are the internal and external structure and the physiognomy of plants adapted to these conditions? ''15 These were Warming's

15. Warming, Lehrbuch, p. 3.

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fundamental ecological questions, and they led to the equally important matter of deciding what are to be the basic units of ecological discourse.

Warming is celebrated for basing ecology on the idea of the plant community. The notion of distinctive plant associations or communities had emerged in the mid-nineteenth century when certain phytogeographers shifted their regard from the accustomed large vegetational units (forest, meadow, moor) to specific units characterized by definite species, vertical structure, and seasonal changes. Anton Kerner von Marilann is recognized as the leader of this movement, and his observations in central Europe contain much of ecological interest) 6 Warming, however, rejected the floristic orientation of this approach and rejected, too, the term "formation," introduced by Kerner and subsequently widely used by other botanists. 17 Formation was an expression too closely tied to systematic and simple description; it failed to capture the living reality of the community.

For Warming the essential units of ecological discourse were the Lebensform, the Verein, and the Vereinsklasse. The principal unit, the Verein, or plant community, was characterized by three features: a definite outward, overall appearance, the physiognomy of the community; a definite general economy, this being a function of the biotic and abiotic features of the group in question; and a definite set of occupying Lebensformen, or life forms. TM The latter lie at the heart of the matter.

In nature, Warming observed, all plants (and animals) exhibit adaptations. These are the very condition of continued existence. The process of adaptation is, of course, interesting from the evolutionary point of view; it is no less crucial to the ecologist. Adaptations reflect not only an organism's adjustment to surrounding conditions, a direct Lamarckian response perhaps, but are profoundly conditioned by "inner, unknown causes," which dictate or prohibit other adaptive possibilities. Warming, in other words, assigned adaptation a dual causation, and from this con-

16. Anton Kerner von Marilaun, Pflanzenleben der Donauldnder (1863), trans. Henry S. Conard, as The Background of Plant Ecology (Ames: Iowa State College Press, 1951).

17. See Knoblauch's comment in Warming, Lehrbuch, p. v; also Warming's observations, ibid., pp. 9--10, 111.

18. Ibid.,pp. 110--114.

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clusion, which he accepted as fact, he drew a further conclusion that truly set the task of the ecologist. Some plants may be perceived as related by genuine affinity, that is, by bonds of genetic connection, and this affinity will usually be expressed by similarity of structure and function. Other plants may be adapted to conditions similar to those under which a different, genetically related set of plants lives. Either way, what results is an assem- blage of plants whose coherence is expressed in adaptations, a common manner or form of life, a shared economy; this is the Lebens form. 19 T h e same "ecological goal" has been reached by different means and by taxonomically and phylogenetically different species. If direct environmental action were the only operative factor, one would expect the occupants of a given locality to respond in similar, even identical, manner. They do not, because each is a unique evolutionary product and possesses a unique fund of, so to speak, ecological potential.

While Warming did not develop these interesting thoughts further, they served to introduce the main course of the Lehrbuch . First, a comprehensive overview of ecological factors and their action was provided. 2° Here was recorded the influence on plants of light, atmospheric temperature and humidity and the movement of air, the physical and chemical properties of the Soil, soil nutrients and moisture content, the effects on the soil of nonliving and living cover, and the activities of animals and plants living in the soil. Among these many possibilities Warming returned repeatedly to the importance of water in the life of a plant and placed the acquisition and retention of water by the plant at the center of ecological analysis. 21 To these factors were then added the crucial dynamics of intraspecific competition, interaction of plant communities, and interaction of plants and animals. 22 In effect, this list of factors, biotic and abiotic, constituted the ecological universe and provided the conceptual apparatus with

19. Ibid.,pp. 3--4. 20. Ibid., pp. 12--93. 21. Water in fact acquired an almost overwhelming influence in Warming's

analysis. A contemporary work with comparable intent provided both a more comprehensive and a more balanced view of ecological factors: see A. F. W. Schimper, Plant Geography upon a Physiological Basis, trans. W. R. Fisher, ed. Percy Groom and I. B. Balfour (Oxford: Clarendon Press, 1903; German ed., 1898).

22. Warming, Lehrbuch, pp. 94-- 119.

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which to assay one or another plant community and to offer an explanation of why such communities are distributed as they are. Warming's purpose, again, was to seek the reasons for the recognized geographic distribution of plants, the answers to be stated in ecological and not historical or broadly phrased evolutionary terms.

One among the several dozen communities reviewed will illustrate Warming's procedure. The Nereiden, or stone-dwelling hydrophytes, are a community of the oceanic and lacustrine littoral. 23 The community consists primarily of algae, but in fresh water mosses and some flowering plants are also encountered. These plants share many features with other submerged hydrophytes. (It was, incidentally, Warming who regularized usage of the terms "hydrophyte," "xerophyte," and "mesophyte.") Plants in this community usually lack woody structural dements and vessels. They also lack stomata, or present these structures in much reduced form. Distinctive adaptations include a range of attach- ment organs, binding plant to substrate; reduced or lost intra- cellular air spaces; and production of calcareous or mucilaginous deposits on the cell surface. Plant shape is highly varied and could not, Warming believed, be explained in terms of adaptation.

It was, however, adaptation that was truly in question. Warming in effect parceled nature into ecological units -- communities -- based on both flora and distinctive abiotic conditions. In the case of the stone-dwelling hydrophytes this entailed consideration of water temperature and movement, salt content, oxygen availability, degree and color of illumination, and consideration of how particlar adaptations permitted occupancy of very specific en- vironments. The result was capture of nature's own product, the plant community. Place and adaptation were the important matters; floristic content and genealogy were not.

The great distributional question had not been posed in this form by leading phytogeographers such as August Grisebach and Oscar Drude. Their approach was descriptive and largely floristic; Warming's approach was ecological and, he hoped, explanatory. In his words, "The ideal [that must guide] scientific treatment of the different plant communities must be to provide a scientific demon- stration of how each member (the several Lebensformen) of a community exists in morphological, anatomical and physiological

23. Ibid., pp. 140--147.

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agreement with the diverse ecological and social conditions under which it lives. ''24 Whether, for example, stone-dwelling hydrophytes were encountered on the rocky coast of California or in a pool beneath a Venezuelan waterfall, in the sea off Jutland or along the shores of a Wisconsin lake, the commonality discerned was that expressed by similarity of structure and function and not by the recurrence of the same species or other taxa. Nature solved similar problems in similar ways, even while using very different raw materials -- that is, different species. The best floristic plant geography might do was record this fact, but Warming, pursuing ecological plant geography, hoped to explain itY

With this point we return to the background theme of virtually all early ecological and much phytogeographic inquiry: descent with modification, including Darwin's explanation thereof. With tongue in cheek, Warming pondered extending his approach to explore all plants and places since the very "creation of the world," a potential evolutionary ecology of extravagant dimensions. This could only have meant a (hypothetical) historical reconstruction of the development of community forms, perhaps of kinds today quite unknown, since the inception of life. Nothing more was heard of this proposal. More pressing was the simple here and now, the emerging ecology of the 1880s and 1890s. The context was evolutionary change. Warming provided no incisive view, recognizing a minor role for natural selection but favoring direct adaptation to the environment and especially the action of an adaptive power internal to the plant, such as had been advocated by Carl yon Nfigeli. Consistent with this view was the conclusion that the spur to evolutionary change was alteration of the earth's surface, a change in climate, soil character, or other "conditions of life. ''26 It was exactly this thesis, of course, that Darwin was led

24. Ibid.,pp. 119--120. 25. Oscar Drude, for one, was not impressed by this approach, granting that

Warming had indeed brought "biology" to phytogeography - - but at the price of rejecting the geography. See Drude, '.'Warming, E. Plantesamfund etc.," review in the Botanische Zeitung, 55 (1897), cols. 33--38.

26. Warming was anything but a systematic evolutionary thinker. He accepted without close assessment the role of direct (environmental) modification, inherit- ed or "phyletic" variability, natural selection, crossing of species, variation following upon correlation of parts, and - - with the second German edition (1902) of the Lehrbuch - - de Vriesian "mutations". See Lehrbuch, pp. 376--382; ibid., 2nd ed., pp. 392--394 (addition by Paul Graebner).

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increasingly to disavow, when after 1856 he pursued ever further the notion of the evolutionary competence of population pressure and the incompetence of the environment. Darwin's final theory, however, diminished the importance of examining the intimate detail of precisely how plants (and animals) interact with one another and with surrounding conditions. While Warming acknowledged a role for competition and differential survival, he more especially wished t o analyze and understand the actual process of interaction - - interaction taken in its broadest sense to embrace organism, community, and environment. His questions were not Darwin's questions, and by the same token Darwin's questions were not intrinsically ecological questions. Those posed by Warming were.

Warming's questions created a new perspective on the general problem o f plant distribution, and his influence was widely felt. August Mentz observed:

For those of us [in Denmark] who were then young and who, through our reading, not least of travel narratives by Humboldt , Grisebach, Darwin, Kerner and others, had acquired a keen sense of floristic-physiognomic plant geography, the introduc- tion to biological plant geography that Warming gave us was something akin to a revelation. His discussion opened for us new points of view; [it gave us an outlook] that in no way conflicted with the data and conclusions of floristic-physiognomic plant geography but which expanded this study and rendered it far more attractive. 27

Warming's specific influence is most obvious in the work of the

While clearly accepting environmental influence, which N~igeli did not, Warming's views coincide on many important points with the latter's mechan- icoidealistic evolutionary hypotheses. See William M. Montgomery, "Germany," in The Comparative Reception of Darwinism, ed. Thomas F. Glick (Austin: University of Texas Press, 1972), pp. 97--106. Despite its seemingly un- promising character, N/igeli's scheme could lend itself profitably to ecological inquiry: inner potentialities could be realized, and only then become evident, if environmental changes had created a new field of opportunity. N~igeli's work stands at the beginning of a century of effort to induce plant transformation by means of transplantation and cultivation in carefully specied localities; this work by the twentieth century had become primarily ecological in character.

27. Mentz, "Warming som plantegeografisk Forsker," p. 39.

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WILLIAM COLEMAN

founders of American plant ecology, Henry Chandler Cowles at Chicago and Frederic E. Clements at Nebraska, and in the varied undertakings of Alfred G. Tansley in Britain. Warming's influence on the Continent has not been assessed, but it is noteworthy that the Lehrbuch appeared in one Polish, two Russian, and three German editions. 2s

Warming's contribution was to refine and thus define a still poorly circumscribed realm of scientific discourse. A man given to sharp polemic and vigorous formulation of positions, his special capacity was conceptualization or, better, reconceptualization. Between the familiar and important study of individual plant anatomy and physiology, his own starting point, and the era's new dispensation, evolutionary change and the many mechanisms proposed for it, Warming discerned the significance of the middle ground, the point at which the evolutionary units, species and communities of species, encountered the limits and possibilities set by the physical world. It is this middle ground that constitutes the special domain of the ecologist.

28. See esp. Ronald C. Tobey, Saving the Prairies: The Life Cycle of the Founding School of American Plant Ecology, 1895--1955 (Berkeley: University of Calfornia Press, 1981), pp. 99--109, 155--190; H. C. Cowles, "A New Treatise on Ecology" [review of Schimper, Pflanzengeographie auf physiologischer Grundlage], Bot. Gaz., 27 (1899), 214--216. Tansley's notion of the ecosystem represents the culmination of efforts to create a complete view of the object of ecological discourse, including reunion of the biotic and abiotic domains. See his "Use and Abuse of Vegetational Concepts and Terms," Ecology, 16 (1935), 284--307. Warming, Tansley reported, opened for him "a new way of looking at the plant world." See his personal appreciation in "Eug. Warming in Memorium," Bot. Tidsskr., 39 (1927), 54--56. The English edition of Warming's work, Oecology of Plants (1909; 2nd ed., 1925), was produced under the supervision of Martin Vahl. Here the language of "formation" returned and many other changes are evident; the edition offers no safe guide to the agrument of the 1896 Lehrbuch, the most widely studied version of the book. The two (different) Russian editions appeared in 1901 and 1903, the Polish in 1900, and the last German edition in 1918.

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evolution into ecology? the strategy of warming's ecological plant geography

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