Henri Lecoq
“When we see the possible alterations in present-day forms, when we reflect upon the profound modifications we have made in the two kingdoms of our domestic races, we cannot really assign any limits to the power of geological causes, to the action of the climate, to the external acting forces, and especially to the different convulsions to which we attribute the mineral waters, the emanations of gas, the volcanoes, the earthquakes, and the upheavals of the mountain ranges.” (Études de la Geographie Botanique de l’Europe, 1854-8)
Henri Lecoq, who trained and practiced as a pharmacist was, in 1827, appointed the chair of natural history for the French municipality of Clermont-Ferrand. Throughout his life, he maintained strong interests in botany, geology and mineralogy. His studies of the paleontological record and plant biogeographical patterns, as well as insights from domestication history, led him to advance species transmutation as the most logical explanation for the distribution of biodiversity both in space and in time.
In the Historical Sketch of On the Origin of Species, Darwin remarked briefly on Henri Lecoq’s 1854 eight volume biogeographical work, Études de la Geographie Botanique de l’Europe. Noting the homage paid to Geoffroy Saint-Hilaire and Goethe in Lecoq’s work, and thus implying the author’s likely affinity for theories of transmutation and metamorphosis, Darwin (who complained that this work had “a great dearth of precise facts”) ended his acknowledgement with: “some other passages scattered throughout M. Lecoq’s large work, make it a little doubtful how far he extends his views on the modification of species”.
Darwin’s apparent indifference (and perhaps too casual a reading of Lecoq) notwithstanding, chapter 11 of volume I (“General considerations on species”) of Lecoq’s treatise on plant biogeography is a full-on defense of descent with modification. Lecoq presents three possible explanations of past and current biodiversity: successive (miraculous) creations, descent with modification (“filiation”), and “translation,” in which some members of already created species are preserved from extinction in the face of environmental catastrophe and are later transported to different parts of the globe to repopulate. Lecoq proceeds to argue for descent with modification as the best possible hypothesis for past and present distributions of species in the fossil record and around the globe.
Arguing that the forces acting in the course of deep geologic time provide “the key to the many phenomena and long transmutations that the brevity of our existence hardly allows us to suspect,” Lecoq suggested that species transmutation constituted a more plausible explanation for the trend in increasing species richness and diversity over time than did the theory of successive special creations in each new geologic era. Drawing on Lamarck and Saint-Hilaire, he wrote that the newer organisms were modified forms of ancestral organisms; and that the changes were wrought, not by mass destruction and new creations, but by evolutionary modification in response to changing environmental conditions.
Invoking a somewhat phylogenetic perspective, Lecoq stated that the “divergent or rather convergent and subordinate classifications, which are the only natural ones, already indicate a tendency for the successive disarticulation of the branches of a common stock, whereas it should not be so if the creations had been simultaneous.” Lecoq’s most compelling argument, however, is based on his and other’s biogeographical work. He wrote that the view of species as being evolutionary derived from one another received “new force from the geographical distribution of animate beings.” Noting that species belonging to the same genera tend to be confined to a particular region, Lecoq reasoned:
“If the creations had been all individual, and if each species had come out as it is now in the hands of the creator, there would be no reason why similar types should not be scattered in all the localities where they might find their conditions of existence. Instead, we see the same dominant forms in this or that region, and the organizational analogies lead us so far, that very distinct and separate localities retain some very particular types.”
Lecoq, like so many of his evolutionist contemporaries did not propose a mechanism by which speciation could occur, invoking instead the nebulous action of “external agents” and “geological and climatic changes.” Nevertheless, his Études de la Geographie Botanique de l’Europe contains a clear caution to readers not to underestimate the effects of deep geological time in producing change in the natural world. Pointing to artificial selection and domestication history, as Darwin himself would do in Origin, Lecoq wrote “When we see the possible alterations in present-day forms, when we reflect upon the profound modifications we have made in the two kingdoms of our domestic races, we cannot really assign any limits to the power of geological causes, to the action of the climate, to the external acting forces, and especially to the different convulsions to which we attribute the mineral waters, the emanations of gas, the volcanoes, the earthquakes, and the upheavals of the mountain ranges.”
All in all, it is not particularly “doubtful how far [Lecoq] extends his views on the modification of species.” He seems to have clearly been an evolutionist.
Count Alexander Keyserling
We are therefore convinced that the chemical constitution of the germinating elements regulates the mode and the number of particles which join by growth. A change in this intimate constitution of the chemical formula of the species, so to speak, would produce a transformed species. (Note sur la succession des êtres organisés, Bulletin de la Société Géologique de France, April 18, 1853)
Count Alexander von Keyserling was among the first of Darwin’s “foreign scientist” acquaintances to receive a complimentary presentation copy of On the Origin of Species directly following its publication in 1859 (DCP-LETT-2505). A Baltic German geologist, known for his geologic expeditions in Russia, Keyserling had previously proposed a unique explanation for the transmutation of species in a brief article “Note sur la succession des êtres organisés,” [Note on the succession of organized beings] in 1853. Keyserling argued that all species possess a unique chemical composition, or signature, which can be modified by the interaction of “foreign molecules” – such as those believed to cause disease – with the “germinating elements.” Or, as Darwin summarized in his Historical Sketch, “as new diseases, supposed to have been caused by some miasma, have arisen and spread over the world, so at certain periods the germs of existing species may have been chemically affected by circumambient molecules of a particular nature, and thus have given rise to new forms.”
Keyserling’s hypothesis about the origin of new species is essentially unique among early evolutionists in arguing that the nature of each species can be tied to a basic set of chemical elements. “For, once we consider organized species as products of the chemical action of different particles or substances on some primitive types, the possible combinations become more and more numerous and complicated; four types, for example, under the influence of twenty-four substances, already produce, by simple combination, 96 species, which, in turn, influenced by 24 bodies, compose a yardstick of 2304 species…” While it is difficult to view this insight as a precursor to knowledge of a genetic code, it nonetheless speaks to an essential relationship between the environment and a chemical blueprint that is determinative of each species on Earth. For Keyserling, a “change in this intimate constitution of the chemical formula of the species, so to speak, would produce a transformed species.”
At the time of Keyserling’s paper, the causes of disease were often attributed to the idea of miasma, or sickness-inducing particles which traveled suspended in the air (this was thought to be the case in the cholera epidemics in 1850s London and Paris). The evidentially real havoc that these particles (miasmas) wreaked on the constitutions of once-healthy individuals suggested to Keyserling the existence of similar chemical packages able to induce a chemical change in the early development of an organism. Keyserling’s theory met with mixed reviews. The hypothesized transformations would be saltational, affecting species around the globe. Keyserling wrote that his theory could explain the destruction and subsequent succession of large swaths of flora and fauna in Earth’s history (major extinction events) through analogy with the episodic nature of various diseases which had arisen and desisted in times past. In addition to accounting for the destruction and replacement of species and the general trend toward increasing complexity, Keyserling argued that his theory solved one of the difficulties which most troubled Darwin – the lack of intermediate forms in the fossil record (which was certainly the case in the mid-1800s).
“[O]ur hypothesis… alone accounts for depletion as well as the replacement of species, without resorting to the fiction of transitory forms; it explains the general extent of the modifications of terrestrial fauna and flora in a similar order of succession in every place; it makes us understand why each of the phases of the organized world of the earth joins, as to the resemblance of the forms, to the preceding and the following more than to all the others; finally, it accords with the increase in the variety and complication of organized beings, through geological epochs, as our research has established.”
Although Keyserling seems to have received Darwin’s gift of On the Origin of Species cordially, he did not do so without critique. As Darwin wrote to Charles Lyell in May of 1860, “I have had a brief note from Keyserling, but not worth sending you: he believes in change of species, – grants that natural selection explains well adaptation of forms, but thinks species change too regularly, as if by some chemical law, for natural selection to be sole cause of change.” With time, however, Keyserling came to appreciate Darwin’s work, and, in 1886 (after Darwin’s death), he wrote that he had come to accept natural selection as the best possible explanation for the origin of new species.
Thomas Henry Huxley
Coming soon.
Joseph Dalton Hooker
Fifteen years before On the Origin of Species would appear in print (1859), Darwin penned a now famous letter to Joseph Hooker, eminent botanist and later Director of the Royal Botanic Gardens, Kew (1865-85). In this letter (January 11, 1844) to his friend, colleague, and confidant, Darwin first shared his thoughts on the mutability of species – “I think I have found out (here’s presumption!) the simple way by which species become exquisitely adapted to various ends” – likening it to “confessing a murder.” From this point on, Hooker became one of Darwin’s most important correspondents, ultimately playing a central role in the dissemination of Darwin’s (and Alfred Russel Wallace’s) theory of descent with modification through natural selection. He, with Charles Lyell, orchestrated the joint communication of Darwin’s and Wallace’s papers to the Linnean Society in 1858 – the first public announcement of the theory of natural selection.
As a prominent 19th century scientist, Hooker clearly understood the import and significance of these ideas, and he became the first published author to advocate Darwin’s and Wallace’s ideas in a remarkable, but today little known essay, the “Introductory Essay to the Flora of Tasmania”. This essay, completed in November, 1859, the same month as Origin, and published the following month, constitutes the first post-Origin era piece of independent scholarship on the processes and patterns of evolution. In 1861, Darwin would write of this essay that Hooker “admits the truth of the descent and modification of species, and supports this doctrine by many original observations.” The botanist F.O. Bower affirmed the originality of Hooker’s contributions in a memorial address delivered the year after Hooker’s death (and reprinted in the University of Chicago’s Botanical Gazette in 1913). Bower argued that “this publication of his belief was not merely an echo of assent to Darwin’s own opinions. It was a reasoned statement, advanced upon the basis of his own ‘self-thought,’ and his own wide systematic and geographical experience. From these sources he drew for himself support for the ‘hypothesis that species are derivative and mutable’” (388).
In many ways, the intellectual journey of Joseph Dalton Hooker in the 1840s and 1850s epitomizes these transformative decades in Great Britain leading up to the publication of On the Origin of Species. Hooker’s publications during this period reveal a man initially skeptical of species immutability, yet seeking the kinds of evidence and proof that might bring rational insight to bear on the question of how species are created.
Read more about Hooker’s contribution to evolutionary thought.
Hooker’s gradual conversion to evolutionism was informed not only by his rich correspondence with Darwin, but also by his own extensive analysis of botanical species and their distribution, critical reading on theories of evolution, and no little amount of intellectual sparring and collaboration with Darwin. During the early critical years when Darwin was formulating his theory, Hooker was working on a massive compilation of the floras of Antarctica, New Zealand, and Tasmania (Botany of the Antarctic Voyage– published 1844-1860) – a result of his field work between 1839 and 1843, when he served as assistant surgeon on the British Antarctic Expedition. The letters exchanged between the two naturalists from 1844 to 1859 are bursting with botanical species to genera ratios, questions of peculiar insular flora, and musings on floral species migration and geographic distribution.
As early as 1844, Hooker wrote to solicit Darwin’s advice, albeit somewhat sardonically, on “what writings on the subject of original creation will give me the best notion of the (mad) theories of some men from Lamarck’s twaddle upwards.” Yet, in his 1853 Introductory Essay to the Flora of New Zealand, Hooker hedges the species question, protesting his “inability to grapple with these great questions” and writing in the chapter “On the Limits of Species; Their Dispersion and Variation:” “It is no part of my present object to discuss the theoretical views that have been entertained on these obscure subjects” (i, vii). He suggests that plant systematists must, for the purpose of classification, consider the specific characters of plants to be constant (i.e unable to transmutate), but maintains that this is for practical and not theoretical reasons and that he is undecided on the question of species permanence: “There are other theories which claim more or less consideration from every unprejudiced naturalist; and there are such theoretical and practical difficulties (and perhaps impossibilities) in the way of our coming to any conclusion as to the limits of the species of many genera, as to give colour to the assumption that they have no permanently recognizable limits” (ix). This early hint at Darwin’s theory is then obscured by a lengthy exposition of arguments in favor of species permanence including the difficulty of producing varieties of plants under cultivation, retention of the same specific characters by widely dispersed plants, and the tendency for allied species to grow together without an apparent interchange of characters.
In an 1855 letter, Hooker wrote to Darwin of his changing views on species creation: “After all it is very easy to talk of the creation of a species in the Lyellian view of creation but the idea is no more tangible than that of the Trinity & to be really firmly & implicitly believed is…a believing in what the human mind cannot grasp. It is much easier to believe with you in transmutation, until you work back to the vital spark-a vis creatrix or whatever you may call it; which is a fact as inscrutable as a full blown species.” By 1859, Hooker’s journey to an evolutionary view of biodiversity was essentially complete, or, at the very least, finally made public. In his 1859 Introductory Essay to the Flora of Tasmania (also reprinted separately from the Botany of the Antarctic Voyage under the title On the Flora of Australia, Its Origins, Affinities, and Distribution; Being an Introductory Essay to the Flora of Tasmania), Hooker forthrightly acknowledges a change of viewpoint from that displayed in his 1853 Essay and openly champions the theory of natural selection put forward by Charles Darwin and Alfred Russell Wallace.
“In the present essay I shall advance the opposite hypothesis, that species are derivative and mutable; and this chiefly because, whatever opinions a naturalist may have adopted with regard to the origin and variation of species, every candid mind must admit that the facts and arguments upon which he has grounded his convictions require revision since the recent publications of the Linnaean Society of the ingenious and original reasoning and theories of Mr. Darwin and Mr. Wallace” (2).
Hooker divided the 1859 Introductory Essay into three sections entitled “On the General Phenomena of Variation in the Vegetable Kingdom,” “On the General Phenomena of Distribution in Area,” and “On the General Phenomena of the Distribution of Plants in Time.” In the first two sections he describes the evidence that he has observed as corresponding to Darwin’s “rationale,” including that there is more tendency to variation in plant species in nature than is usually accounted for; the ability of horticulturalists to turn cultivated plant species into new varieties; that plant species which do not survive in nature die because of their inability to compete with their “enemies;” and the general tendency of plants to radiate out from an area of common geographical origin. In the final section on the “Distribution of Plants in Time,” Hooker is more reticent, admitting that paleobotanical evidence “is not altogether favorable to the theory of progressive development, both because the earliest ascertained types are of such high and complex organization, and because there are no known plants which we can certainly assume to belong to a non-existing class or even family, nor that are ascertained to be intermediate in affinity between recent classes or families” (23).
Still, this does not prevent Hooker from leading up to his remarkable conclusion that “…if, as I have endeavored to show, all those attributes of organic life which are involved in the study of classification, representation, and distribution, and which are barren facts under the theory of special creations, may receive a rational explanation under another theory, it is to this latter that the naturalist should look for the means of penetrating the mystery which envelopes the history of species, holding himself ready to lay it down when it shall prove as useless for the further advance of science, as the long serviceable theory of special creations, founded on genetic resemblance, now appears to me to be” (26).
Darwin commented extensively on Hooker’s manuscript versions of the Introductory Essay to the Flora of Tasmania, writing to him with concerns about Hooker’s seeming to quote Origin which had not yet been published –“I am far more than satisfied at what you say of my work; yet it would be as well to avoid the appearance of your remarks being a criticism on my fuller work” – and complimented Hooker on his “grand” essay which would “convert botanists from the doctrine of immutable creations”. (To read in-depth correspondence between Hooker and Darwin during these crucial years, please visit the Darwin Correspondence Project and the Hooker Correspondence Project).
The American botanist Asa Gray, reprinted Hooker’s Introductory Essay in the American Journal of Science and Arts, writing in a footnote on the very first page:
“I asked and have received the distinguished author’s permission to reprint them…that we may have before us, at the earliest date, an essay which cannot fail to attract the immediate and profound attention of scientific men…To those who have intelligently observed the course of scientific investigation, and the tendency of speculation, it has for some time been manifest that a restatement of the Lamarkian hypothesis is at hand. We have this, in an improved and truly scientific form, in the theories which, recently propounded by Mr. Darwin, followed by Mr. Wallace, are here so ably and altogether independently maintained. When these views are fully laid before them, the naturalists of this country will be able to take part in the interesting discussion which they will not fail to call forth” (1).
As Asa Gray points out, in The Flora of Australia, Hooker’s conviction in the theory of natural selection is “altogether independently maintained”. Nor was Asa Gray the only botanist with whom Hooker corresponded about the theory of natural selection on the basis of his own botanical evidence. In an 1860 letter to the Irish botanist William Henry Harvey, Hooker advises him to “Remember that I was aware of Darwin’s views fourteen years before I adopted them, and I have done so soley and entirely from an independent study of the plants themselves” (Life and Letters, italics in original text). Harvey was reluctant to accept natural selection as cause of the establishment of particular plant varieties, but Hooker reminded him not to confuse natural selection with variation itself. Drawing on his own experience of the intellectual journey from species fixity to transmutation, Hooker writes, “I am extremely anxious that you should not commit yourself in your present state of very partial knowledge and strong feelings on a subject that requires years of thought and the calmest study, and above all a singleness of mind in seeking for truth at all hazards” (Life and Letters).
Although largely remembered as Darwin’s confidant and Director of the Royal Botanical Gardens at Kew during the peak of the British empire, Hooker played a critical role in the early history of evolutionary thought. He was central to the intellectual sparring and critique that helped Darwin advance his own case for transmutation. Perhaps equally important, Hooker was also in his own right one of the leading minds scrutinizing the evidence for and against an evolutionary explanation of life, and penning a critical piece of independent scholarship to bolster the case of descent with modification in 1859.
Isidore Geoffroy Saint-Hilaire
Coming soon.
Henry Freke
Coming soon.
Lucretius
Nature dos allthings change, & forces to
Transforme. (De Rerum Natura)
On the Nature of Things (De Rerum Natura), the magnificent Epicurean poem by the Roman philosopher Lucretius, contains a number of passages in book V that speak to an evolved world. Lucretius was an atomist who believed in free will (the random swerves of atoms precluded a strictly mechanical or predestined world) and rejected the notion that there is a designer or creator of the universe. Lucretius was strongly antagonistic to organized religion, and argued that when the body dies, so too does the soul (there is no afterlife).
A few examples of passages that describe a world constantly changing and evolving follow below. There is even what might be viewed as a rudimentary concept of natural selection, in which mutant forms of life, if maladapted, are eliminated (though this passage lacks the generative force of better adapted forms giving rise to new kinds). Although modern English translations abound, I have chosen the earliest English translation – by none other than John Evelyn, the diarist and author of the first book published by the Royal Society of London: Sylva or a Discourse on Forest-Trees, and the Propagation of Timber in His Majesty’s Dominions (1664). Who better to capture the meaning of trees and their rise to prominence? Also, the concern that translations post-1859 might inadvertently reflect the modern perspective of natural selection is thus obviated by choosing a translation from the 1650s (from Repetzki, M.M. 2000. John Evelyn’s Translation of Titus Lucretius Carus De rerum natura).
First the Earth cloth’d with herbs the little hills,
Whose pleasant verdure all the surface fills,
And shining with its rich inamel spreads
The florid fields, and the luxurious meads;
Trees without checq did plentifully spring…
For Age at length dos chang the face
And nature of the World, & every thing
Doth from one state unto another bring,
Nor doth ought like it selfe remaine, all goe,
Nature dos allthings change, & forces to
Transforme. For one thing rotts, & with age dyes;
Another growes, & from contempt doth rise.
Thus age doth change the World, & from one state
Unto another dos the Earth translate;
So that what once it could, it cannot now,
And now dos what to doe it knew not how.
The Earth strang Monsters then to make did trye
Of different looks & members ametrie,
Hermophrodite, a kind that is betwixt
And equaly remote from either Sex,
Some without feete, some hand-lesse, Mouthlesse, blind,
Others whose parts were so to th’ body joyn’d
They could not move, no function could performe,
Nor take things for their use, nor flie from harme.
Such Monsters & Portents she made in vaine,
For Nature, to augment them did disdaine
Nor could th’ arrive to age’s perfect state,
Nor find their nourishment, nor Copulate;
For divers things must first concur we see
E’re things by propagation specifie:
First nourishment, & then the genial seede
Which flowing may from laxid parts proceede,
And parts for mutual pleasure them assign’d
So that the femal with the male be joynd.
Else divers sorts of Animals had dyed
E’re this, nor could their race have multipli’d:
For all you see to live & breath the aire
By craft, or force, or nimblenesse, they were
Preserv’d from the beginning: And againe
Many commended to our care remaine
Because of the utilitie…
Although the first translation of On the Nature of Things from Latin into English was by John Evelyn, he only published the first book of the six books that make up the poem. The remainder of his translation remained in manuscript until published in 2000. The first published full translation, by John Creech, appeared in 1682, with a second edition (pictured here) published a year later.
Alfred Russel Wallace
Alfred Russel Wallace, codiscoverer of the principle of natural selection was also the founder of the field of biogeography. Like Charles Darwin, he too had a vast experience of field work in South America (four years of professional collecting from 1848 – 1852). And like Charles Darwin, he too would credit the reading of Malthus’ On Population as a central stimulus for the key insight of natural selection. Wallace would live a long life. Beyond his remarkable insights into evolutionary biology, he would also be widely known for his ardent advocacy of spiritualism, land nationalization, anti-vaccinationism, and for much of his later life, a highly teleological view of evolution.
Before Charles Darwin published his first clear (and public) statements on evolution in 1858 and 1859, Alfred Russel Wallace had already published a series of brilliant papers that bear on the process of evolution and species formation. The first of these papers (1855) “On the Law which has Regulated the Introduction of New Species” was to have an enormous impact on the thinking of Charles Lyell. The other papers, “On the Habits of the Orang-Utan of Borneo” (1856), “Attempts at a Natural Arrangement of Birds” (1856), “On the Natural History of the Aru Islands” (1857), “Note on the Theory of Permanent and Geographical Varieties” (1858) represent the most important published scholarship on evolution in the decade leading up to the Wallace and Darwin publications on the process of natural selection.
There are many recent biographies of Alfred Russel Wallace. In addition, there are excellent websites with extensive information about the life, scholarship and collections of Wallace: The Alfred Russel Wallace Page, The Alfred Russel Wallace Website, and the Wallace Collection.
There are many photographic portraits of Alfred Russel Wallace, spanning his extremely long life. Some were published in his books of the late nineteenth century and early twentieth centuries. There are also portraits that were used for cartes-de-visite (as is the case for the center portrait below).
Herbert Spencer
Herbert Spencer was best known in the nineteenth century as a philosopher and social theorist. He is now remembered for his key role in the development of concepts of social Darwinism and as the originator of the term “survival of the fittest” (which Darwin first included in the fifth edition of On the Origin of Species). Between 1851 and 1859, Herbert Spencer published a series of important papers that dealt directly with evolution per se – as well as its extension to all other things. They remain a most enjoyable set of readings: Lyell and Owen on Development (1851), The Development Hypothesis (1852), Progress: Its Law and Cause (1857), Owen on the Homologies of the Vertebrate Skeleton (1858), and Illogical Geology (1859). Herbert Spencer’s book Principles of Psychology (1855, read the first edition here) appears to be the first serious attempt to address the evolutionary underpinnings of mental properties.
For a concise review of Herbert Spencer’s evolutionary views, see P. J. Bowler’s Evolution, The History of an Idea (third edition) pages 220 – 223.
Herbert Spencer’s concise and memorable response to creationist attacks on evolutionary facts and theory from his 1852 paper published in The Leader.
Matthias Jakob Schleiden
Matthias Jakob Schleiden was Professor of botany at the University of Jena and is best known as one of the foundational architects of the cell theory. Schleiden was also an early evolutionist. As Schleiden wrote in a lecture on the “History of the Vegetable World” published in The Plant; A Biography, 1848 (translated into English by Arthur Henfrey), “We know that varieties once formed, when they have continued to vegetate under the same conditions for several generations, pass into sub-species; that is, into varieties which may be propagated with certainty by their seeds. How, then, if the same influences which have called forth an aberration from the original form of the plant, continue to act in the same way, not for centuries or tens of centuries, but for ten or a hundred thousand years, will not at last, as the variety thus becomes a sub-species, so also, this, become so permanent, that we shall and must describe it as a species. Then, if the first cell be given, the foregoing points out how the whole wealth of the vegetable kingdom may have been formed by a gradual passage from it through varieties, sub-species and species, and thus onward, beginning anew from each species – in a space of time, indeed, of which we have no conception.”
Baden Powell, in his book on evolution (1855), quoted from The Plant to support his transformist views. Ironically, when Charles Darwin was working with Heinrich Georg Bronn to arrange for a German translation of On the Origin of Species in 1860, he wrote “I am not much acquainted with German Authors as I read German very slowly. Therefore I do not know whether any Germans have advocated similar views with mine; if they have would you do me the favour to insert a footnote to the Preface?” Bronn did not supplement Darwin’s historical preface. Thus, even though Schleiden’s evolutionary views were published in English, he never was cited by Darwin as an early evolutionist.
Frontispiece of the German edition of Schleiden’s book die Pflanze und ihr Leben, published in 1848. A well-developed discussion of plant evolution can be found in the thirteenth lecture, on the history of the plant world (link to 1855 German edition).
Frontispiece of the English edition of Schleiden’s book The Plant; A Biography, published in 1848. A well-developed discussion of plant evolution can be found in the eleventh lecture, on the history of the vegetable world (link to 1855 English edition).