Category Archives: Botany

November 29, 1627

John Ray

On this date, the naturalist and Anglican priest John Ray was born at the village of Black Notley in the county of Essex in England. He is often referred to as the father of natural history in Britain.

Ray published systematic works on plants, birds, mammals, fish, and insects, in which he brought order to the chaotic mass of names in use by the naturalists of his time. A basic problem of classification was to decide how much apparent variation can be allowed to plants or animals grouped as a single species. How can one know whether or not two individuals share the “same essence?” Ray’s most influential decision was to define a species as a group of organisms that reproduce the same traits from seed. He wrote in Historia plantarum generalis (1686):

In order that an inventory of plants may be begun and a classification of them correctly established, we must try to discover criteria of some sort for distinguishing what are called “species.”  After long and considerable investigation, no surer criterion for determining species has occurred to me than the distinguishing features that perpetuate themselves in propagation from seed. Thus, no matter what variations occur in the individuals or the species, if they spring from the seed of one and the same plant, they are accidental variations and not such as to distinguish a species … Animals likewise that differ specifically preserve their distinct species permanently; one species never springs from the seed of another nor vice versa.

This was the first recorded biological definition of “species.”

Like Linnaeus (1707-1778) whom he later inspired, Ray searched for the “natural system,” a classification of species that would reflect the “divine order of creation.” Unlike Linnaeus, whose plant classification was based entirely on floral reproductive organs, Ray classified plants by overall morphology; the classification in his book Methodus Plantarum Nova (1682) draws on flowers, seeds, fruits, and roots. In other words, Ray rejected the method of dichotomous division by which species were classified according to a series of pre-conceived, “either/or” criteria, and instead classified plants according to similarities and differences that emerged from observation. As a result, Ray’s plant classification was the first to group flowering plants into what are today known as monocots and dicots. His method produced more “natural” results than “artificial” systems based on one feature alone; it expressed the similarities between species more fully.  Ray’s system greatly influenced later botanists such as Jussieu and de Candolle, and systems based on total morphology came to replace systems based on only one feature or organ system. Eventually, Ray’s use of total morphology to classify species would become a powerful tool in the hands of evolutionary biologists trying to infer evolutionary relationships.

A devout Christian of his time, Ray was clearly a creationist. In his book The Wisdom of God Manifested in the Works of Creation (1691), he explained that intricate contrivances like the eye or the hand could not have arisen by chance. Instead, they were designed. And their “perfection” displays the wisdom and benevolence of the Designer. Yet Ray did not define species in terms of special creation, as he explained in a letter to his friend Pfaff:

We imagine that a species is the total descendence [sic] of the first couple created by God, almost as all men are represented as the children of Adam and Eve. What means have we, at this time, to rediscover, the path of this genealogy? It is assuredly not in structural resemblance. There remains in reality only reproduction and I maintain that this is the sole certain and even infallible character for the recognition of the species.

A different aspect of Ray’s work represented another huge advance for science. Whereas many medieval and later theologians had taught that the natural world distracted people from salvation and should be avoided, Ray affirmed powerfully that Nature was a worthy subject for study and reason, and that such activity was pleasing to God. Expounding his belief in “natural theology,” Ray wrote in his Catalogue of Cambridge Plants (1660):

There is for a free man no occupation more worthy and delightful than to contemplate the beauteous works of nature and honour the infinite wisdom and goodness of God.

Also, unlike many academics of his day, Ray cautioned against blind acceptance of authorities; in The Wisdom of God, he wrote:

Let it not suffice to be book-learned, to read what others have written and to take upon trust more falsehood than truth, but let us ourselves examine things as we have opportunity, and converse with Nature as well as with books.

Unlike Linnaeus, who focused almost exclusively on classification for its own sake, Ray began to use classification to address questions in physiology, function, and behavior. He understood that living things showed adaptations to their environments.

References:

  • Ernst Mayr, The Growth of Biological Thought: Diversity, Evolution, and Inheritance (Cambridge, MA: Harvard University Press, 1982) pp. 256-7.
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November 18, 1810 (a Sunday)

Asa Gray By John Whipple, 1864

On this date, America’s leading botanist in the mid-nineteenth century, Asa Gray, was born. On a visit to England in 1851, Gray met for lunch with Charles Darwin, and they formed a lasting connection. When Gray returned to the United States, he was able to see that North American plant life had evolved under the disruption of the ice age. In a famous letterto Gray dated September 5, 1857, Darwin wrote:

As you seem interested in subject, & as it is an immense advantage to me to write to you & to hear ever so briefly, what you think, I will enclose (copied so as to save you trouble in reading) the briefest abstract of my notions on the means by which nature makes her species. Why I think that species have really changed depends on general facts in the affinities, embryology, rudimentary organs, geological history & geographical distribution of organic beings. In regard to my abstract you must take immensely on trust; each paragraph occupying one or two chapters in my Book. You will, perhaps, think it paltry in me, when I ask you not to mention my doctrine; the reason is, if anyone, like the Author of the Vestiges, were to hear of them, he might easily work them in, & then I shd’have to quote from a work perhaps despised by naturalists & this would greatly injure any chance of my views being received by those alone whose opinion I value.—…

Gray was the third scientist Darwin told of his theory (after Hooker and Lyell). [Less than a year later, both Darwin and Wallace publicly proposed that evolution occurred by natural selection. It was Darwin’s good luck that his early correspondence with Gray showed that he had been first to articulate the idea.] The depth of their friendship was evident in a letter dated January 23, 1860 concerning the help the American botanist wished to give Darwin in presenting his book to the American public. In this letter Gray wrote:

Your candor is worth everything to your cause. It is refreshing to find a person with a new theory who frankly confesses that he finds difficulties, insurmountable at least for the present. I know some people who never have any difficulties to speak of. The moment I understood your premises I felt sure you had real foundation to hold on. Well, if one admits the premises, I do not see how it is to stop short of your conclusions, as a probable hypothesis, at least.

In 1856, Gray published a paper on the distribution of plants under the title Statistics of the Flora of the Northern United States; and this paper was followed in 1859 by a memoir on the botany of Japan and its relations to that of North America, a paper of which Sir J. D. Hooker said that “in point of originality and far-reaching results [it] was its author’s opus magnum.” Gray’s discovery of close affinities between East Asian and North American floras was a key piece of evidence in favor of evolution. He explained this disjunct distribution pattern by suggesting that New England and temperate Asia had once been geographically continuous and had had a uniform flora which only diverged after the areas were separated by later geological events. This hypothesis has not only held up, supported by the discovery of continental drift and plate tectonics, it has also proved fruitful enough to provide a basis for current and important research in vicariance biogeography.

From 1855 to 1875, Gray was both a keen critic and a sympathetic exponent of Darwin’s theory of evolution. His religious views were those of the Evangelical bodies in the Protestant Church; so that, when Darwinism was attacked as equivalent to atheism, he was in position to answer effectively the unfounded allegation that it was fatal to the doctrine of design. He openly avowed his conviction that the present species are not special creations, but rather derived from previously existing species; and he made his avowal with frank courage, when this truth was scarcely recognized by any naturalists, and when to the clerical mind evolution meant atheism. The Rev. R. W. Church, the Dean of St. Paul, had met Gray in 1853 and later wrote about his life-long friend:

His religious views were a most characteristic part of the man, and the serious and earnest conviction with which he let them be known had, I am convinced, a most wholesome effect on the development of the great scientific theory in which he was so much interested. It took off a great deal of the theological edge, which was its danger, both to those who upheld and those who opposed it. I am sure things would have gone more crossly and unreasonably if his combination of fearless religion and clearness of mind and wise love of truth had not told in the controversy.

Gray wrote numerous botanical textbooks and works on North American flora, including Flora of North America that he co-authored with his mentor John Torrey.

References:

  • Charles Darwin, letter to Asa Gray, September 5, 1857; Reprinted in Frederick Burkhardt, ed., Charles Darwin’s Letters: A Selection 1825-1859 (New York: Cambridge University Press, 1996) 177-179.
  • “New Publications; Asa Gray’s Life and Letters: Letters of Asa Gray,” The New York Times (Wednesday, November 19, 1893) 23.

November 15, 1871 (a Wednesday)

Erich Tschermak von Seysenegg

On this date, the Austrian agronomist Erich Tschermak von Seysenegg was born.  He was one of the scientists, the others being Hugo De Vries and Carl Correns, who independently rediscovered the work that Gregor Mendel did in the 1860s on the laws of heredity.  Von Seysenegg published his findings in June 1900.  The priority of Mendel was acknowledged without restriction by all three researchers.  Mendel’s discovery that inheritance is particulate, and confirmation of his discovery by Von Seysenegg, De Vries, and Correns, constitutes one of the main pillars of the theory of evolution.

November 4, 1855 (a Sunday)

Frederick Orpen Bower

On this date, the botanist Frederick Orpen Bower was born in Ripon, England. His study of primitive land plants, especially the ferns, contributed greatly to a modern emphasis on the study of the origins and evolutionary development of these plants. A man who did not shy away from theorizing, one of his most productive “working hypotheses” was his application of the alternation of generations model to explaining the way the land was colonized by early plants. This subject was explored most completely in his book entitled The Origin of a Land Flora: A Theory Based upon the Facts of Alternation, published in 1908.

From his many years studying liverworts, mosses, and ferns, Bower concluded that they had evolved from algal ancestors. Bower’s hypothesis states, in essence, that the sporophyte generation (the conspicuous vegetative stage in familiar vascular plants) developed de novo from a haploid alga that lacked a diploid sporophyte generation but instead had merely a diploid zygote (a cell formed by the fusion of two gametes, such as sperm and egg). Before the evolution of embryos, this zygote would have immediately undergone meiosis (to relieve the diploid condition) and produced spores, the propagules of the next haploid generation. Growth of such a spore into a gametophyte is analogous to growth of an isolated human sperm or egg cell into a hypothetical haploid generation. Thus, the sporophyte generation first appeared as an added generation that came into existence as a result of delayed zygotic meiosis – sort of a delayed plant puberty. In other words, what might otherwise have become the new haploid cells of the next generation by chromosome reduction instead retained its diploid character and thus added, aà la Bower, a new generation to the life cycle. The final step of spore production still eventually occurred, but not until after the diploid cells had grown and developed into a new sporophyte generation, in essence an overgrown zygote.

Under Brower’s hypothesis, we suppose that, from the point of view of the gametophyte, the sporophyte generation is like a giant multicellular spore factory. For example, in Coleochaete pulvinata, a modern freshwater green alga, the surface of the mature zygote is covered by a layer of haploid cells, which form ingrowths that penetrate the zygote to provide nutrition. The protected diploid zygote in Coleochaete gives the aquatic alga advantages because many more spores can be produced from a single fertilization event than would be the case if the zygote hurried straight to meiosis and the formation of one of those four spore tetrads so common in the fossil record. Bower’s hypothesis remains to be tested, but if it is correct, the sporophyte generation (diploid cells) came to develop inside (and be protected by) the gametophyte generation (haploid cells) precisely because the arrangement ultimately benefited both generations.

An older, competing hypothesis dating back to 1874 held that the algal ancestor of embryophytes already had had alternation of two generations for a long time and was thus diplobiontic, as opposed to haplobiontic. Haplobiontic organisms, such as humans, have the gametes as the only haploid cells; diplobiontic organisms develop those haploid cells into a multicellular life stage. The diplobiontic hypothesis of 1874 is less favored now because it fails to explain how the sporophytes and gametophytes, which in modern diplobiontic green algae have no long-term physical connection, could have evolved the intimate physical connection, in both nutritional and developmental respects, shared by the haploid and diploid components of all embryophytes.

Bower’s other publications included Ferns (three volumes, published 1923-28) and Primitive Land Plants (1935). Bower was elected Fellow of the Royal Society in 1891 and was awarded the Linnean Medal in 1909, the Royal Medal in 1910, and the Darwin Medal in 1938, the latter “In recognition of his work of acknowledged distinction in the field in which Darwin himself laboured.”

October 22, 1783 (a Wednesday)

Constantine Samuel Rafinesque

On this date, the naturalist Constantine Samuel Rafinesque was born in Galata, a suburb of Constantinople. Throughout his life he traveled extensively, collecting specimens wherever he went, and wrote and published constantly. He was an overly enthusiastic but accurate observer driven by a monomaniacal desire to name every object he encountered in nature. His scientific work has been gaining more and more recognition in recent years.

Rafinesque’s family moved to France the year following his birth, and at age nineteen Rafinesque became an apprentice in the mercantile house of the Clifford Brothers in Philadelphia. He returned to Europe in 1805 and spent the next decade in Sicily, where he was secretary to the U. S. consul. During this time his first scientific books were published. He returned to the United States in 1815 and remained in America the rest of his life, becoming a naturalized citizen in 1832. He was professor of botany and natural science at Transylvania University in Lexington, Kentucky from 1819 to 1826.

The early conclusion by Rafinesque that the taxonomic categories called species and genera are man-made generalizations which have no physical existence led to his deep appreciation of variation in plants. He understood that such variation, through time, will lead to the development of what we call new species. But he had no explanation for the cause of variation, though he did consider hybridity a possible mechanism and, without calling it that, he had what appears to be some perception of mutation. Hence, he never developed a theory of evolution earlier than Darwin, as sometimes has been claimed, because Rafinesque had no inkling of natural selection and his understanding of geological time was far too shallow.

September 19, 1864 (a Monday)

Carl Erich Correns

On this date, the German botanist and geneticist Carl Erich Correns was born. He is famous for rediscovering, independently of but simultaneously with the biologists Erich Tschermak von Seysenegg and Hugo De Vries, Gregor Mendel’s historic paper outlining the principles of heredity.

In 1892, while at the University of Tübingen, Correns began to experiment with trait inheritance in plants. On January 25, 1900, he published his first paper, “G. Mendel’s Law Concerning the Behavior of the Progeny of Racial Hybrids”, in which he restated Mendel’s results and his law of segregation and law of independent assortment. Although the paper cited both Charles Darwin and Mendel, Correns did not fully recognise the relevance of genetics to Darwin’s ideas.

In attempting to determine the extent to which Mendel’s laws are valid, Correns undertook a classic study on heredity in the four-o’clock plant (Mirabilis jalapa). The blotchy leaves of these variegated plants show patches of green and white tissue, but some branches carry only green leaves and others carry only white leaves. Whether a tissue is green or white depends on whether there are green or white chloroplasts in the cytoplasm of its cells. Flowers appear on all types of branches, and Correns performed a variety of crosses.

Two features of his results were surprising. First, unlike what Mendel had observed, Correns found that there was a difference between reciprocal crosses, that is, leaf color depended greatly on which parent (i.e., flower’s branch) had which trait. Such results are normally encountered only for sex-linked genes, but Correns’ results cannot be explained by sex linkage. Secondly, the phenotype of the maternal parent was solely responsible for determining the phenotype of all progeny, that is, the phenotype of the male parent appeared to be irrelevant, making no contribution to the progeny at all! Although the white progeny plants did not live long because they lacked chlorophyll, the other types of progeny did survive and could be used in further generations of crosses. The same patterns of maternal inheritance always appeared in these subsequent generations.

Maternal inheritance can be explained if the chloroplasts are somehow genetically autonomous and furthermore, are never transmitted via the sperm. This is reasonable since the chloroplasts come exclusively from the mother in most angiosperms. In his 1909 paper, Correns established variegated leaf color as the first conclusive example of cytoplasmic inheritance (cases in which certain characteristics of the progeny are determined by factors in the cytoplasm of the female sex cell), also known as extrachromosomal or non-Mendelian inheritance.

Unfortunately, most of Correns’ work went unpublished and was destroyed in the Berlin bombings of 1945.

July 20, 1822 (a Saturday)

The earliest known photograph of Gregor Mendel.

On this date, Gregor Johann Mendel was born (the day he was baptized, July 22nd, is often given erroneously as his birthday). He performed a series of beautifully designed experiments on pea plants over a period of seven years, from 1856 to 1863, to discover the principles of heredity. His studies were the first to focus on the numerical relationships among traits appearing in the progeny of hybrids; and his interpretation, clear and concise, was based on material hereditary elements that undergo segregation and independent assortment.

Mendel delivered two lectures on the results of his experiments at the meetings of the Society of Natural Sciences in Brünn, Austria on February 8th and March 8th in 1865. He turned these lectures into a (long) paper, published in the 1866 issue of the Proceedings of the Society, but it received little notice. Mendel apparently even sent one of his scientific papers to Darwin, but Darwin never bothered to read it. Mendel abandoned his experiments in the 1860s after he was appointed abbot of his monastery and his time was taken up in administrative duties.

The importance of Mendel’s work was not recognized until about thirty years after the publication of his seminal paper, when Hugo de Vries in 1900 in Holland, William Bateson in 1902 in Great Britain, Franz Correns in 1900 in Germany, and Erich Tschermak in 1901 in Austria were all to acknowledge Mendel’s legacy, and hail him as the true “father” of classical genetics.

Curiously, proponents of Intelligent Design (ID) theory have attempted to appropriate Mendel. Steve Fuller openly declares that ID theorists “would do well to reclaim the likes of Newton, Linnaeus, and Mendel as their own” (2007, p 7). Fuller claims that Mendel was no evolutionist, but a “special creationist with a grasp of probability theory”. For Fuller, the Mendelian rules of heredity are laws designed by God, that define “the range of traits that God deemed permissible in a given species”.

The only occasion that Mendel expressed himself directly on the subject of evolution was in an examination paper he sat in 1850. Discussing the origin of plant and animal forms, in the context of the formation of the earth, he wrote:

As soon as the earth in the course of time had achieved the necessary capability for the formation and maintenance of organic life, plants and animals of the lowest sorts first appeared.

[In time, organic life] developed more and more abundantly; the oldest forms disappeared in part, to make space for new, more perfect ones.

[This is] at the present time the generally accepted view of the emergence and development of the earth (Orel 1984, pp 237-8).

This is far from any “creationism” (even “special creationism”).

When he wrote this, he had been a monk for seven years. He finished his studies at the University of Vienna three years later, in 1853; began his Pisum experiments in earnest in 1856; and did not deliver his talk on those experiments until 1865. Of course, his ideas may have changed in time—and in any case, the views expressed in an examination may not always reflect the writer’s real opinion; but in the absence of any other statement by Mendel on the origin of species, this would appear to undermine any notion that he was a “special creationist.”

References:

  • Fisher, R.A. “Has Mendel’s work been rediscovered?Annals of Science, v. 1: 115-137 (1936)
  • Fuller, Steve (2007). Science vs. Religion? (Cambridge: Polity Press).
  • Orel, Vitěslav (ed.) (1984). ‘Mendels Hausarbeit in Naturgeschichte von 1850’. In: Folia Mendeliana 18 (Special edition).

June 30, 1817 (a Monday)

Joseph Hooker (seated, far left) and on the ground next to him, Asa Gray – 2 of the first 3 men to whom Darwin revealed his theory of evolution by natural selection (July, 1877 U.S. Geological Survey at La Veta Pass, CO)

On this date, the physician, botanist, and biogeographer Joseph Dalton Hooker was born in Halesworth in the county of Suffolk, England. He trained as a doctor in Edinburgh, but his principal interest was in botany.

Joseph Hooker (1896)

Hooker was a close friend and supporter of Charles Darwin. When he realized that Alfred Russel Wallace was about to present his findings on evolution to the public which were similar to Darwin’s, he helped arrange for the shared presentation of Darwin ‘s and Wallace’s papers to the Linnaean Society of London in 1858.

Hooker came to America in 1877 to explore the flora of the Rocky Mountains of Colorado and the Sierra Nevada Mountains of California. He traveled to Pueblo, Colorado with a group of colleagues including Asa Gray. Later, Hooker traveled to La Veta Pass, CO and camped with a group of naturalists and explorers. The group later traveled to the Sangre de Cristo range where Hooker and Gray conducted a plant survey and wrote a manuscript about their experience, The Vegetation of the Rocky Mountain Region and a comparison with that of other parts of the World (1880).

May 25, 1769

Jan Ingen-Housz

On this date, the Dutch physician and scientist Jan Ingen-Housz was elected to the Royal Society of London. He is best known today for showing that light is essential to photosynthesis and thus having discovered photosynthesis. He also discovered that plants, like animals, have cellular respiration.

In the summer of 1771, Joseph Priestley had carried out experiments with air and jars, noting that a closed jar would eventually kill a mouse and extinguish a candle, but vegetation (he used mint) would allow the mouse to live and the candle to burn. Although he did not have the official names of the “types” of air he was observing, Priestly had discovered that mice and candles need something (oxygen), and plants are capable of using other things in the air (carbon dioxide) to produce that something. In short, plants restore to the air whatever breathing animals and burning candles remove.  However, Priestly and others were unable to reproducibly demonstrate oxygen production by plants because they were unaware of the requirement for light in photosynthesis.

Probably motivated by Priestley’s publications on the subject, Ingen-Housz obtained a short leave of absence in 1779 from his post in Vienna, Austria in order to do research in England on plants during the summer months. He performed more than 500 experiments trying to determine why plants restore bad air and described the results in his exceptional book entitled Experiments Upon Vegetables, Discovering Their Great Power of Purifying the Common Air in the Sunshine and of Injuring it in the Shade and at Night, published in October 1779.

Underwater plants producing bubbles of oxygen.

In some of his experiments, Ingen-Housz placed plants underwater in a transparent container.  He found they gave off bubbles of gas only when placed in sunlight and that the bubbles gradually ceased when the plants were placed in darkness. He determined that it is not because of the warmth of the sun, and it is not the sun acting on its own, but the light of the sun reacting with the green parts (stalks and leaves) of the plants.

Once he realized a gas was being produced in the presence of light, Ingen-Housz collected it and conducted a series of tests to determine its identity. He eventually discovered that a smoldering candle would relight when it was exposed to the unknown gas. This showed that it was oxygen (known at that time as ‘dephlogisticated’ or ‘vital’ air).

In another experiment, Ingen-Housz put a plant and a candle into a transparent closed space. He allowed the system to stand in sunlight for two or three days. This assured that the air inside was pure enough to support a candle flame. But he did not light the candle. Then, he covered the closed space with a black cloth and let it remain covered for several days. When he tried to light the candle it would not light. Ingen-Housz concluded that somehow the plant must have acted in darkness like an animal. It must have breathed, fouling the air. Ingen-Housz quickly printed his book in London, allowing him to take along copies when he returned to Vienna.

The biochemistry of photosynthesis.

So why is Priestley until today a well-known name in the history of science, while Ingen-Housz is virtually unknown , except for a few historians of chemistry and botany? Ingen-Housz was a humble person, not interested in fame, pomp, or circumstance. Low-key and introverted, enjoying friendships, shying away from stardom, he stood in contrast to some of his fellow researchers of that time. For example, Priestley admitted in private that Ingen-Housz indeed had been the first to describe the beneficial power of plants in a letter to Giovanni Fabroni from 1779:

I have just read and am much pleased with Dr. Ingenhousz’ work. The things of most value that he hit upon and I missed are that leaves without the rest of the plants will produce pure air and that the difference between day and night is so considerable.

Priestley promised Ingen-Housz that he would rectify the situation in a later publication. But the attribution never appeared in print; Ingen-Housz was not even mentioned by Priestley. In the meantime, Priestley repeatedly claimed in public to have observed and published before Ingen-Housz and kept repeating this until 1800. In fact, never did Priestley give an accurate reference to Ingen-Housz’ work, never did Ingen-Housz’ name appear in the index of Priestey’s works. On the other hand, Ingen-Housz systematically referred to Priestley, with much respect.  Ingen-Housz refrained from disputing the claims of his rival colleagues, but they continued as they did, obfuscating Ingen-Housz’ rightful place in science as the discoverer of photosynthesis in the eyes of the historians and the public.

References:

April 18, 1865 (a Tuesday)

Karl Wilhelm von Naegeli, the man who discouraged Gregor Mendel from further work on genetics.

Karl Wilhelm von Naegeli, the man who discouraged Gregor Mendel from further work on genetics.

On this date, Austrian monk Gregor Mendel, 42, sent the results of his seven-year study of peas to the eminent biologist Karl Wilhelm von Nägeli in Munich. Within these results were the basic laws of genetics, which the humble Mendel discovered single-handedly in a small garden at the Brünn monastery (now in Brno, Czech Republic). Nägeli failed to see the importance of the work; he suggested that Mendel try new experiments with different plants. Nägeli’s cool reception, coupled with the failure of the new experiments, were instrumental in Mendel’s abandoning serious research.

April 12, 1748 (a Friday)

Antoine Laurent de Jussieu (1748-1836)

On this date, the French botanist Antoine Laurent de Jussieu was born in Lyon. He proposed the first natural system of classifiying flowering plants (angiosperms), much of which remains in use today.

In his study of flowering plants, Genera plantarum (1789), Jussieu adopted a methodology based on the use of multiple characters to define groups, an idea derived from Scottish-French naturalist Michel Adanson. This was a significant improvement over the original system of Linnaeus, who classified plants into families based on the number of stamens and pistils. Jussieu did keep Linnaeus’ binomial nomenclature, resulting in a work that was far-reaching in its impact; many of the present-day plant families are still attributed to Jussieu. For example, Morton’s 1981 History of botanical science counts 76 of Jussieu’s families conserved in the ICBN, versus just 11 for Linnaeus.

April 8, 1805 (a Monday)

Hugo von Mohl

On this date, the German botanist Hugo von Mohl was born in Stuttgart. In 1823, he entered the University of Tübingen. After graduating with distinction in medicine he went to Munich, where he met a distinguished circle of botanists and found ample material for research. Unmarried, Mohl’s pleasures were in his laboratory and library, and in perfecting optical apparatus and microscopic preparations, for which he showed extraordinary manual skill. He suggested using the term protoplasm for the ground substance of cells – the nucleus had already been recognized by Robert  Brown and others, but Mohl showed in 1844 that the protoplasm is the source of those movements which at that time excited so much attention.

The origin of the cell was unknown in Mohl’s time. Schwann had regarded cell growth as a kind of crystallization, beginning with the deposit of a nucleus about a granule in the intercellular substance – the “cytoblastema”, as Schleiden called it. But Mohl, as early as 1835, had called attention to the formation of new vegetable cells through the division of a pre-existing cell. Ehrenberg, another high authority of the time, contended that no such division occurs, and the matter was still in dispute when Schleiden came forward with his discovery of “free cell-formation” within the parent cell, and this for a long time diverted attention from the process of division which Mohl had described. All manner of schemes of cell-formation were put forward during the ensuing years by a multitude of observers, and gained currency notwithstanding Mohl’s reiterated contention that there are really but two ways in which the formation of new cells takes place – namely, “first, through division of older cells; secondly, through the formation of secondary cells lying free in the cavity of a cell.”

But gradually the researches of such accurate observers as Unger, Nageli, Kolliker, Reichart, and Remak tended to confirm Mohl’s opinion that cells spring only from cells, and finally Rudolf Virchow brought the matter to demonstration about 1860. His Omnis cellula e cellula became from that time one of the accepted facts of biology.

Mohl’s early investigations on the structure of palms, cycads, and tree ferns permanently laid the foundation of all later knowledge of this subject.  His later anatomical work was chiefly on the stems of dicotyledons and gymnosperms. He first explained the formation and origin of different types of bark, and corrected errors relating to lenticels. Following his early demonstration of the origin of stomata (1838), Mohl wrote a classical paper on their opening and closing (1850). He received many honors during his lifetime, and was elected foreign fellow of the Royal Society of London in 1868.

April 7, 1727 (a Monday)

Michel Adanson

On this date, the French botanist Michel Adanson was born. Following study at the Plessis Sorbon, the Collège Royal, and the Jardin du Roi, Adanson traveled to Senegal where he spent four years collecting natural history specimens. The report of this expedition appeared in 1757 as Histoire naturelle du Sénégal, and it contained a novel systematic arrangement of mollusks that won Adanson some notoriety in zoological circles. He is best remembered, however, for his comprehensive Familles des plantes (Paris, 1763–1764), in which he rejected systems (such as those of Linnaeus) that were based on only a few selected characters (artificial systems), in favor of an arrangement that takes all features of the plant into account (a natural system). As an associate of Buffon, Adanson was a significant contributor to the Historie naturelle, and his own herbarium, numbering about 30,000 specimens, came to rest in Paris at the Muséum National d’Histoire Naturelle.

February 23, 1863 (a Monday)

Chamberlain and Cycads in the University of Chicago Greenhouse

Chamberlain and Cycads in the University of Chicago Greenhouse

On this date, the American botanist Charles Joseph Chamberlain was born near Sullivan, Ohio. His research into the structure and life cycles of primitive plants (cycads) enabled him to suggest a course of evolutionary development for the egg and embryo of seed plants (spermatophytes) and to speculate about a cycad origin for flowering plants (angiosperms).

Chamberlain first studied botany and zoology at Oberlin College. After spending several years as a school teacher and administrator, he entered the University of Chicago where in 1897 he received the first doctorate in botany awarded by that institution. He organized and directed the botanical laboratories at the University of Chicago (1897-1931), where, with plants collected in Mexico, Australia, New Zealand, South Africa, and Cuba, he created the world’s foremost collection of living cycads. His comprehensive work entitled Gymnosperms: Structure and Evolution was published in 1935.

February 16, 1848 (a Wednesday)

Hugo de Vries

On this date, the Dutch botanist and early geneticist Hugo Marie de Vries was born. He is known chiefly for suggesting the concept of genes, rediscovering the laws of heredity in the 1890s while unaware of Gregor Mendel’s work, for introducing the term “mutation”, and for developing a mutation theory of evolution.

In 1889, De Vries published his book Intracellular Pangenesis, in which, based on a modified version of Charles Darwin’s theory of pangenesis of 1868, he postulated that different characters have different hereditary carriers. He specifically postulated that inheritance of specific traits in organisms comes in particles.

De Vries conducted a series of experiments hybridizing varieties of multiple plant species in the 1890s. Unaware of Mendel’s work, De Vries used the laws of dominance, segregation, and independent assortment to explain the 3:1 ratio of phenotypes in the second generation. His observations also confirmed his hypothesis that inheritance of specific traits in organisms comes in particles.

In the late 1890s, De Vries became aware of Mendel’s obscure paper of thirty years earlier and he altered some of his terminology to match. When he published the results of his experiments in the French journal Comtes Rendus de l’Académie des Sciences in 1900, he neglected to mention Mendel’s work, but after criticism by Carl Correns he conceded Mendel’s priority. Thus, Correns, Erich Tschermak von Seysenegg, and De Vries now share credit for the rediscovery of Mendel’s laws.

February 5, 1799 (a Tuesday)

On this date, the English botanist and horticulturist John Lindley was born. His attempts to formulate a natural system of plant classification greatly aided the transition from the artificial system (considering single or few characters of a plant species) to the natural system (considering all characters of the plant).

Illustration from Lindley’s book entitled "Sertum orchidaceum: A Wreath of the Most Beautiful Orchidaceous Flowers" (1837-41).

Illustration from Lindley’s book entitled “Sertum orchidaceum: A Wreath of the Most Beautiful Orchidaceous Flowers” (1837-41).

In 1818 0r 1819, Lindley went to London, where he was engaged by J. C. Loudon to write the descriptive portion of the Encyclopaedia of Plants. In his labors on this undertaking, which was completed in 1829, he became convinced of the superiority of the “natural” system of A. L. de Jussieu, as distinguished from the “artificial” system of Linnaeus followed in the Encyclopaedia; the conviction found expression in A Synopsis of British Flora, arranged according to the Natural Order (1829) and in An Introduction to the Natural System of Botany (1830).

February 3, 1857 (a Tuesday)

Wilhelm Ludvig Johannsen

On this date, the Danish botanist and geneticist Wilhelm Ludvig Johannsen was born. His experiments in plant heredity offered strong support to the mutation theory of the Dutch botanist Hugo de Vries (that changes in heredity come about through sudden, discrete changes of the heredity units in germ cells). Many geneticists thought Johannsen’s ideas dealt a severe blow to Charles Darwin’s theory that new species were produced by the slow process of natural selection.

Johannsen explained his ideas in his book entitled On Heredity and Variation (1896), which he revised and lengthened with the rediscovery of Gregor Mendel’s laws and reissued as The Elements of Heredity in 1905. The enlarged German edition of this work was published in 1909 and became the most influential book on genetics in Europe. In it, Johannsen coined the terms “gene”, “phenotype”, and “genotype”.

January 26, 1792 (a Thursday)

Robert Brown as a young man.

On this date, the Scottish botanist Robert Brown read his first scientific paper entitled “The botanical history of Angus“, to the Edinburgh Natural History Society, although it was never published in print in his lifetime.  He was born on 21 December 1773, so that he was but a little over eighteen when he read this essay.  Later in life, he made important contributions to science largely through his pioneering use of the microscope.

In 1827, while examining pollen grains under a microscope, Brown observed minute particles within vacuoles in the pollen grains executing a continuous jittery motion. He then observed the same motion in particles of dust, enabling him to rule out the hypothesis that the effect was due to pollen being alive. Although Brown did not provide a theory to explain the motion, and Jan Ingenhousz already had reported a similar effect using charcoal particles in German and French publications of 1784 and 1785, the phenomenon is now known as “Brownian motion.”  [In 1905, Albert Einstein postulated that Brownian motion was direct evidence of molecular action, thus supporting the atomic theory of matter.]

The cell.

Robert Brown is perhaps most famous for identifying a structure within cells that he named the “nucleus” in a paper read to the Linnean Society of London  in 1831 and published in 1833. Furthermore, he suggested that the nucleus may be an essential component of the cell. He discovered the nucleus while studying orchids microscopically, in the cells of the flower’s outer layer. The nucleus had been observed before, perhaps as early as 1682 by the Dutch microscopist Leeuwenhoek, and Franz Bauer had noted and drawn it as a regular feature of plant cells in 1802, but it was Brown who gave it the name it bears to this day (while giving credit to Bauer’s drawings). Neither Bauer nor Brown thought the nucleus to be universal, and Brown thought it to be primarily confined to Monocotyledons.

January 6, 1906 (a Saturday)

George Ledyard Stebbins, Jr.

On this date, the American botanist and geneticist George Ledyard Stebbins, Jr. was born in Lawrence, New York. He is widely regarded as one of the leading evolutionary biologists and botanists of the twentieth century. His most important publication was Variation and Evolution in Plants (1950). It is regarded as one of the main publications which formed the core of the modern evolutionary synthesis and still provides the conceptual framework for research in plant evolutionary biology; according to Ernst Mayr, “Few later works dealing with the evolutionary systematics of plants have not been very deeply affected by Stebbins’ work.” Stebbins was passionate about teaching evolution, advocating during the 1960s and 70s the teaching of Darwinian evolution in public schools. He worked closely with the Biological Sciences Curriculum Study to develop high school curricula based on evolution as the central unifying principle in biology. He also opposed scientific creationism groups.

December 16, 1859 (a Friday)

Bryophytes on brook.

On this date, the American botanist Douglas Houghton Campbell was born. He was an expert on the anatomical structure and life cycles of mosses, ferns and liverworts. Throughout his entire life, Campbell was interested in the evolution of vascular plants, which he thought occurred on land from primitive mosses. He also studied the modern geographic distribution of plants.

At a time before it was generally accepted, Campbell thought Wegener’s theory of continental drift (proposed in 1912) was plausible. Campbell recognized that a primordial supercontinent, Gondwana, splitting into smaller land masses that drifted apart would resolve many of the puzzling facts in geographical distribution, both of animals and plants:

Acceptance of the recent hypothesis of Du Toit, that there were two primordial continents, Laurasia in the Northern Hemisphere and Gondwana in the South, and from these primary continents, the existing continents were separated and shifted to their present positions, would, if true, remove most of the difficulties in explaining the present distribution of many existing plant families.

References:

  • Douglas Houghton Campbell, “Relations of the temperate floras of North and South America,” Proceedings of the California Academy of Sciences 25, 4th ser. (1944): 139-146.

What is the smallest seed in the world?

HINT: It’s not the mustard seed!

The orchid Gomesa crispa.

The world’s smallest seeds, which have no endosperm and contain underdeveloped embryos, are produced by certain epiphytic orchids (family Orchidaceae) in the tropical rainforest. Some seeds are only 1/300th of an inch (85 micrometers) long, which is below the resolving power of the unaided human eye. One seed weighs only 1/35,000,000th of an ounce (0.81 micrograms). Orchid seeds are dispersed into the air like minute dust particles and come to rest in the upper canopy of rainforest trees, where they eventually germinate.

On the other hand, the seed of the begonia plant is about 1/100th of an inch in size, that of the petunia plant about 1/50th of an inch, and that of the mustard plant (family Brassicaceae) about 1/20th of an inch.

By the way, this is what Jesus of Nazareth said about the mustard seed:

With what can we compare the kingdom of God, or what parable will we use for it? It is like a mustard seed, which, when sown upon the ground, is the smallest of all the seeds on earth; yet when it is sown it grows up and becomes the greatest of all shrubs, and puts forth large branches, so that the birds of the air can make nests in its shade. (Mark 4.30-32) [emphasis added]

Some have argued, despite the clear language of the quote, that Jesus was only referring to the seeds known to his audience. Well then, was the mustard seed the smallest seed known in Palestine? No, not even in Jesus’ time. There would be numerous plants familiar to his audience with smaller seeds, of which the best example would be the seed of the black orchid. And just for the record, the mustard seed doesn’t grow to be the greatest of all the shrubs on Earth, either.

The point of this observation is not to attack Jesus of Nazareth; the point is to attack those who would put words in his mouth. Jesus was not a scientist. Keeping in mind the fact that the Bible has been copied and translated so many times that it is likely we will never know for sure what he actually said, I think we can agree that Jesus spoke allegorically and not literally when he said that the mustard plant has the smallest seed on Earth, and that it is the largest shrub on Earth. Nor did Jesus ever claim that the Earth was created 6,000 years ago with species unchanging and in their modern forms – he did not declare evolution to be false.