Footsteps: Cells as the Basis for Life

(All Life, not just Plants)

Construction of this Essay was inspired by Suddhartha Mukherjee’s The Gene – An Intimate History; Randy Wayne’s Plant Cell Biology, from Astronomy to Zoology; and Henry Harris’s The Birth of the Cell

The National Human Genome Research Institute reports that humans and bananas share 60% of their genetics. 

Though so completely different in architecture and lifestyle, humans share many characteristics with a full grown oak tree. We are both made of cells, around 30 trillion of them each. Glucose, and the mechanisms that allow us to use simple carbohydrates for building components and energy storage are owned by the oak as much as by any human. And our cells follow a similar organizational nature, with the same basic mechanisms of inheritance and control. In fact, just being alive and having nuclei demands a lot of regulation, such that, genetically, the oak and a human probably differ by less than 50%. The implications of this sharing are that somewhere, way back in your family tree, you share an ancestor with the oak.

So what is the science behind this? How did we come to such an understanding about ourselves and oaks? When did this become standard knowledge? What were the steps to progress; who made the discoveries? What does information about humans tell us about our distant relatives in the plant kingdom? How does knowing this history help us to understand science today?

It really all started with sex. Or perhaps it was wine. Toward the end of the 17th century (1665), Robert Hooke published a significant book titled Micrographia, reporting his examinations of many objects. For this discussion, it is important that Hooke was the first person to use a microscope in determining that a part of a plant (a piece of cork, maybe from a wine bottle) is divided into microscopic chambers, which he called cells.

Later, Hooke wrote: “These pores, or cells, were not very deep.. I no sooner discerned these (which were indeed the first microscopical pores I ever saw, and perhaps that were ever seen, for I had not met with any writer or person that had made any mention of them before this) be me thought I had with the discovery of them presently hinted to me the true and intelligible reason of all the phenomena of cork.” (Taber, 2007. To Cork or Not to Cork) 

This is a bit problematic for those of us who teach biology, because we know it is normal to bring up Anton von Leeuwenhoek as the inventor of the microscope, and as the first person to reveal the microscopic world to science. But trust me, Robert Hooke scooped von Leeuwenhoek when it comes to cells.  Significantly, Hooke studied cork in sufficient detail to speculate that a cubic inch would be composed of 1,200,000,000 cells. He had a beautiful desktop microscope (with magnification of about 50x) at a time that von Leeuwenhoek was mounting the special glass lenses he learned to make in little portable handheld gimbals. Sometimes its useful to have a lot of funding.

Just six years after Micrographia appeared, it became apparent that serious studies in plant anatomy were flourishing. Nehemiah Grew published Anatomy of Vegetables Begun (followed a decade later by his tremendous Anatomy of Plants.)  In the same year, Marcello Malpighi published Anatome Plantarum Idea. Both authors continued improving their work, which seemed sufficiently solid that a century would pass before plant cells got much additional attention. Early plant anatomy, however, peaked too soon.  Though there were curious moments and discoveries worth noting, over a century later, in 1800, we knew very little more of significance about cells than people had learned from Grew and Malpighi.

In other areas of investigation, things were not so complacent. Born the same year as Hooke published Micrographia, German botanist Rudolf Camerarius went to work at the botanical gardens in Türbingen, where his observations of plant flowering and seed set led to the 1694 publication of a scientific letter on sexual reproduction in plants (De sexu planetarum epistola). Camerarius probably knew little about cells as the stuff of plants. But his observations of plant reproduction kindled a great amount of interest, capturing the attention of scientists, and changing everything we understand about plants.

Camerarius‘ s ideas took off. The concept that plants have sex, and the flower is a nuptial bed where marriages are sexually consummated, became a core theme for Linnaeus, the 18th century’s premier plant Systematist. This is likely the reason Henry Baker, one of the few productive plant microscopists of the 18th century, paid so much attention to pollen (which he called farina). Both hybridization studies and pollination ecology gained their start with the detailed work of Joseph Koelreuter (also of Türbingen), who was following up on ideas developed at the gardens there. (see: Sophie C. Ducker and R. Bruce Knox, 1985. “Pollen and Pollination: A Historical Review”, Taxon, Vol. 34, No. 3 (Aug., 1985), pp. 401-419 Published by: International Association for Plant Taxonomy (IAPT) Stable URL:https://www.jstor.org/stable/1221207

As late as 1800, the structure and workings of cells remained yet a mystery, partly due to simple limitations in optics. Microscopy had remained more a hobby than the core aspect of science it would soon become. The early 19th Century was a watershed period; in 1807 Link described plant cells as functioning independently. By 1830 botanists and zoologists were beginning to explore the nature of cells, with improvements in microscopy and microtechnique emerging quickly..

And the sex thing continued to spark life in that study, particularly in pollen and pollen tube development. Robert Brown, known for his floristic work in Australia, was not in the line of great microscopists, but he was very interested in pollen. In a study of burst pollen grains, published in 1827, Brown reported observations that matter under a microscope moves (like it vibrates or jiggles), even when there is no obvious external force, an inherent movement physicists today refer to as Brownian Motion. Just a few years later, in 1831, while studying pollen and pollen germination, he described the presence of a body, an “aureole” or a “nucleus” he called it. Here we have confirmation that cells are not just hollow bubbles. They corral nuclei, and other things.

Granted, Brown had no idea as to a function for his nucleus, or that there were other kinds of bodies inside plant cells. But his simple observation was at the very cusp of a great epoch in microscopy, both plant and animal. By 1835, Hugo von Mohl (who had been appointed a Professor of Botany at Türbingen) reported that cells reproduce themselves, an observation he made through his studies of the green alga Cladophora glomerata.

Ideas from many labs coalesced in what we, today, call the “cell theory” – that is: “all living organisms are composed of cells.”   Matthias J. Schleiden (botanist), Theodor Schwann (a zoologist), and Rudolf Virchow (pathologist) gain credit for first enunciating cell theory, but further investigation reminds us Schwann and Schleiden were not always the most astute.

However, they were (along with Virchow) the “Colonizers” who managed to create impact based on their own work, as well as the contributions of many less vocal researchers. Even though people argue as to who should get the credit, the new understanding highlighted in Schwann’s 1839 book Microskopische Untersuchengen über die Uebereinstimmung in der Struktur und dem Wachsthum der Thiere in Pflanzen, signals that botany and zoology began to merge as biology – a word that had only been around since 1802.

The cellular nature of plants and animals inspired researchers and drove development of new techniques. Microscopy matured as its own field; a scientific understanding of the production, structure, and activities of cells became the holy grail. As late as 1850, however, microtechnique remained somewhat primitive, and cell biology did not even exist as a field of study.

Hugo von Mohl and his cohorts were famous for using fresh hand-cut sections to make observations, but their slide preparations could not be stored over the long term – they were not permanent because microtomists used sugar solution for mounting. And even though early studies (Hooke, 1665; Hill, 1770) had made use of natural dye, it wasn’t until the second half of the 19th century that botanists fully-adopted the use of stain technologies.

Moreover, life sciences were in an uproar in many regards; one most pertinent to this discussion was Charles Darwin’s 1859 publication – The Origin of Species by means of Natural Selection or the Preservation of Favorite Races in the Struggle for Life   Darwin’s work has become a tenant of faith for biologists, which has different meaning to us today, as compared to what was implied at its debut. Notice that even the book title might be something of a surprise. In contemporary discussion, we skip over the subtitle (which I made bold for emphasis).

Darwin clearly understood that circumstances could favor reproductive success of one form or variant as compared to another. Over time, that could lead to evolution of a different kind of plant or animal, a new species. But he did not have evidence as to what mechanism allowed for stable inheritance, while also creating diversity between individuals within a population. This mystery be-deviled Darwin, and challenged others.

Curiously, a missing piece to Darwin’s puzzle was known as early as 1865, when Gregor Mendel had presented and then published (1866) his studies of hybridization and inheritance. Mendel even communicated with noted scientists, who seemed unwilling to give his work much credence, which meant his observations, data, and conclusions were moth- balled for 35 years. While Mendel’s calculations on inheritance lingered in limbo, however, the next three decades were not silent in other regards.

Considerable advances were made in understanding cell structure and biology. Studying white blood cells at the University of Türbingen, Swiss biochemist Friedrich Miescher isolated and characterized nucleic acids – compounds we would later know as DNA and RNA. By 1879, using the new aniline stains for microtomy, Walther Flemming was able to describe chromatin threads (strands of unconsolidated chromosomes), associating them with the nucleus. Furthering his studies, in 1882, Flemming’s significant book, Zellsubstanz, Kern und Zelltheilung (Cell substance, nucleus and cell division) utilized the term “mitosis” and proved nuclei give rise to new nuclei – “omnis nucleus e nucleo.” Following up on Flemming’s work, Wilhelm von Waldeyer-Hartz observed and named chromosomes as cellular bodies made of chromatin in 1888. None of these researchers understood the structure of chromosomes, or their relationship to inheritance.

Chemically, Albrecht Kossel followed up on Miescher’s discovery of nucleic acids, publishing important work beginning in 1895, in which he characterized and named the five nucleobases scientists would later understand constitute the coding imbedded in nucleic acids.

In the last decade of Mendel’s exile, Darwin enthusiast, Dutch botanist Hugo de Vries, set about searching for clues to underpin Darwin’s half-hearted concept of pangenesis (suggesting inheritance from everywhere, hypothesizing diffuse corpuscles that would somehow come together to launch an egg or sperm).  De Vries began numerous trials, culminating in a series of publications. His 1897 Hereditary Monstrosities indicated that a trait, however one defines a trait, would be managed by a discrete parcel of information. This paralleled efforts that began early in the decade, when he launched a series of trials with 50,000 seed from a population of Oenothera lamarckiana, dedicating 8 years to a search for variants. Additionally, he had been working on studies of plant hybrids. De Vries was in the middle of these heady labors when he was sent a copy of Mendel’s paper. There it was, de Vries had been scooped 30 years before, while he was still a teenager. During his entire career, Mendel’s publication had been sitting on the library shelf.

By the end of the century, de Vries work was destined to corroborate the work of others, bringing context to Mendel’s research. Studies of cell biology, molecular structure, and inheritance were now linked. With growing realization that the basis of inheritance is the same for all life forms, discoveries informed each other across silos – work with plant breeding and selection increasingly was important to people studying human disease; studies of fruit flies were foundational for plant biologists.

This became obvious early in the new century, which dawned with scientific renewal as researchers resurrected and tuned into the implications of Mendel’s work. This was, truly, a great scientific “Aha!” moment. Connecting the dots between Mendel, Darwin, and what had been learned about chromosomes and cell biology quickly brought realization that the world of biological understanding had undergone a paradigm shift, or a sea change, or something truly significant. William Bateson the most effective proponent of Mendel’s work, announced to an audience of the Royal Society in 1900: “We are in the presence of a new principle of the highest importance… To what further conclusions it may lead us cannot yet be foretold.”

Among the first to corroborate Mendel’s ideas was the young botanist at Türbingen, Carl Correns. Working with Hawkweed (Hieracium), Correns published his observations on inheritance of traits early in 1900, citing both Mendel and Darwin.

Correns worked under Nägeli at Türbingen. It was Nägleli with whom Mendel had corresponded, and Nägeli who suggested Mendel work with Hawkweed. Mendel’s attempts in studying Hawkweed had been frustrating, a frustration that likely correlates with Correns’ conclusions about the non-Mendelian effects of linkage (assortment is not random, rather two different genes are linked due to physical proximity on chromosomes.) Of course, the most frustrating part of Correns’ career must have been that Nägeli never shared with him that he knew all about Mendel’s work. Coreens would encounter Mendel’s publication on his own.

Theodor Boveri and William Sutton are credited with introducing the “Chromosome Theory of Inheritance” in 1902, recognizing chromosomes as the carriers of inheritance. In short order, we are told, Bateson christened this field as “genetics” in 1905 while Wilhelm Johannsen coined the term “gene” in 1909, to represent a unit of inheritance – whatever that might be. (Worth pointing out, in 1893 Charles Bessey referred to “genetic relationships” in his address to the US National Academy of Sciences.  This suggests the field of study was termed “genetics” well before 1905.)

Through this first generation of researchers whose work was informed directly by the exhumation of Mendel’s publication, additional realizations snowballed, some of which would quickly challenge the simplicity of Mendel’s obserevations.

Post-Mendelian Reality: Succeeding generations of geneticists explored territory well beyond a focus on the nature of inheritance. What are the basic sources of selection, or selective pressure? How does selection impact speciation in smaller populations, in founder populations, on islands? What does a gene do, like how does the information in a gene get translated into real activity? If every cell with a nucleus has all of an organism’s genetic information, what happens to control events during growth and development. What regulates the activity of genes? How much information is there in a genome? As a physical entity, how does a gene layout in the chromatin? And, importantly, how can we goose the larder? What tools are available to humans that can be employed to change the future?

Answers to those questions continue, as new tools and techniques are aligned with ever-increasing funding to explore and conquer the very secrets of life. In this new world of cell biology, breakthroughs are compounded as discovery and realization in one area informs work in all others. Solving problems and answering questions means finding the useful organism. Historical disciplines of Botany and Zoology retain meaning, but mainly in organismal (systematics, ecology, natural history) and applied (agriculture, medical care) studies.

At a cellular and molecular level, it almost boils down to con- venience.  Mendel had struck gold with Peas… , while Nägeli’s pressure for him to work with Hawkweed killed that momentum. The next organism to spur advances was the Fruit Fly, Drosophila melanagaster.  Thomas Hunt Morgan, a researcher at Columbia, was interested in how an organism emerges from a single cell and had elected to pursue that line of research through studying Fruit Flies for many reasons, most obviously their short generation times (10 days) and ease of culture.

Turning the attention of his lab to mutations that could be studied genetically, researchers in Morgan’s lab were successful in many endeavors. By 1913, team member Alfred Sturtevant had published the first genetic map. In the 13 years since rediscovery of Mendel’s work, researchers working synchronously had gone from the simplest realization that chromosomes carried genetic instructions to having mapped genetic control of characteristics to identifiable regions of chromosomes.

But 1914 brought the War to End All Wars, which of course led to a second World War in 1939. Research advances moved to North America as some of Europe’s greatest science talent and knowledge scattered or died. Integrally linked to four decades of war lull was the painful shadow of eugenics, which drew so many brilliant minds to the dangerous edge of inhumane application of genetic manipulation of human populations and society.

Somehow, with so much effort directed to the war machine, advances in certain areas of pure science continued. Most particularly, technologies improved. Imagery available from TEM (transmission electron microscopy) and SEM (scanning electron microscopy) evolved, promising much greater detail as to structural features. Molecular techniques advanced in refinement, separation, and analysis. Researchers could delve more deeply more and precisely into cellular activity, teasing out new realizations, such as the role and mechanism of hormones, the complex sequences of photosynthesis, the perception and processing of environmental cues.

And people had to be fed, so agricultural research advanced, especially in the United States. This was integral with the reality that Zea mays (Corn in the US, Maize in the rest of the world) became a model plant for genetic study.  Maize is one of the great grasses that feed the world; rice, wheat, and maize together constitute 60% of calories in the human diet. But more than that, maize has become a molecular goldmine, the source of oils and carbohydrates that power machinery, sweeten and cook foods, create plastics, etc.

Food security underwrote studies of healthy eating. Working at Stanford University and funded partially by military monies to study nutrition, George Beadle and Edward Tatum experimented with bread molds to test their one-gene-one-enzyme hypothesis (made in 1941), suggesting that a gene corresponds to production of a protein. At the close of WWII, in 1945, Beadle and Tatum published results supporting that concept.

Concomitantly, Oswald Avery, Colin MacLeod, and Maclyn McCarty (working at the Rockefeller Institute) provided evidence in 1944 that DNA (deoxyribonucleic acid) is the genetic material that researchers have sought. Somehow, DNA held life’s blueprints. Understanding that chromosomes housed linear arrays of genetic information, and realizing that genes somehow correlate to proteins, the search was on for the molecular system that could provide and actualize instructions (templates) to create build and operate cells. This heralded a period of post-war advances, as lab groups across Europe were re-energized. Alfred Hershey and Martha Chase published studies in 1952 bolstering Avery-MacLeod-McCarty conclusions that genes are somehow embedded in DNA. Studies by Watson, Crick, and Franklin brought structural reality to the discussion in 1953 by explaining the double helix architecture of DNA, and the pairing of nucleobases.

By the early 1960s, the role of RNA in transcription had been explained and in 1965 the code was cracked. Researchers in various labs had competed to complete understanding as to how triads of the five “canonical” nucleobases (plus variants) generate matches for the 20 amino acids that constitute proteins. Suddenly, scientists could sequence DNA and interpret the message, which determined what protein would be transcribed from each functional gene in the DNA.

Just as suddenly, a new reality dawned. Not all sequences are created equal. There are nonsense segments, and repeated sequences. A gene might not even consist of contiguous sequences. If all genes are present in linear but non- straightforward formats, how is order achieved? What regulates developmental sequences? How are genes controlled? When is a gene activated? Who’s incharge?

It turns out that the life of each cell is multi-variately integral. Earlier thoughts that cells were filled with air, or water, or slime were successively informed with greater detail. At magnifications we can only approach through electron micros- copy, organelles and membranes scientists discovered in the 19th century were now seen to be integrated with complex membranes and tubules forming a cytoskeleton, like the ropes, ladders, and platforms of the world’s most elaborate high wire act. Nothing really floats through fluid or void, rather components are guided and positioned with microprecision.

The numerous elements in this structural schema and the ways in which communication and signaling occur continue to come into focus, but great strides have been made over recent decades. By 1953, through electron microscopy, many work- ers had detailed and Kevin Porter had named the endoplasmic reticulum, a membranous network Garnier first noted in 1897.

After several years of work, in 1961 Wilhelm Menke deter- mined there was a regular structure to stacks of membranes in the grana of chloroplasts, which he name thylakoids. Appreciating the internal structure of chloroplasts led to work that has further explained how photosynthesis systems function.

Moreover, by 1968 scientists had learned that chloroplasts (and other plastids) carry their own DNA, which became part of many stories, from evolutionary studies that depend on maternal inheritance to providing greater support for Lynn Margulis’ proposals (1967) regarding the origins of organelles such as chloroplasts and mitochondria.

In the 1960s researchers began to make progress on structure and function of the Golgi complex, another mysterious cell feature named for Camillo Golgi, who first described it in 1897. Today the membranous Golgi complex is viewed as a multifarious and adaptable factory for cell components, such as membranes, proteins, and carbohydrates.

Ultimately, setting aside the semi-independent organelles, components of cellular cytoplasm can be viewed both as membranous workbenches that translate nuclear instructions into physical compounds and as antennae for stimulus response. These platforms are embedded in a soft fluid and, along with organelles, are manipulated through microtubular and actin motors. Internally, the chloroplasts and mitochondria replicate this organizational logic, in yet more miniature and compact versions.

Finally, despite initial concepts that cells function independently (even though united in tissues), Tangl had observed the presence of intercellular connections by 1879, which Strasburger confirmed and named as plasmodesmata in 1901. The assumption of completely independent cells has fallen. By 1930, Münch had expressed the concept of a symplast (united cytoplasmic tissue) as contrasted with the apoplast, though further real appreciation of material movement between cells would await development of electron microscopy and advanced staining techniques. Even now there remain points of discussion regarding structure and function of intercellular connections, and the basis of our understanding of living organisms continues to emerge. (A. G. Roberts and K. J. Oparka, 2003. “Plasmodesmata and the control of symplastic transport” Free Access, Plant, Cell & Environment, 26(1): 103- 124)

In the end, energy is harnessed and order is achieved. Materials are manufactured, stored, and retooled. Cells thrive or survive, and manage to recreate and reinvent themselves so that multicellular second order forms evolved.  And that is life, which “is not found in atoms or molecules or genes or such, but in organization”  (Edwin Grant Conklin, 1940. “Cell and protoplasm concepts: Historical account,” in: F. R. Moulton, ed. The Cell and Protoplasm. Washington, DC: The Science Press.)

Detailed Plant Cell Biology & Genetics Time- Line

1614 Galileo had adapted lenses from telescopes to study small objects (Harris, 1999)

1619 Protestant John Andreas notes: “If you do not analyze matter through experiment, if you do not improve knowledge through better instruments, you are worthless.” (Harris, 1999)

1624 Cesi (a Lincean) described lens systems in Italy devised to investigate small objects.(Harris, 1999)

1665 In his Micrographia, Robert Hooke detailed the structure of cork and described “cells” as studied through a microscope that had been constructed for him. This is recognized as the first time the word cell was applied to what we now understand is the basic unit of life, though the cork Hooke studied was composed of dead cells, and he had no idea as to the con- tents and organization future research would reveal.

1671 Nehemiah Grew’s The Anatomy of Vegetables Begun, was received by London’s Royal Society about the same time an abstract arrived from Marcello Malpighi, which covered his studies of both plants and animals. Malpighi would send additional material to the Royal Society for publication in 1675 and 1679, informing Grew’s studies significantly. In his 1999 book, The Birth of the Cell, Henry Harris notes that Malpighi made important observations of plants, but reminds the reader that his contributions to zoology are more fundamental, that he is, perhaps: “the founding father of microscopic zootomy, as well as phytotomy.” It was Malpighi who first described pulmonary capillaries, explaining the connection between veins and arteries and resolving the major question surrounding Harvey’s proposed model for blood circulation. Malpighi’s plant studies were heavily influenced by his knowledge of animal anatomy, thus Malpighi is the author who applied the term tracheid to xylem vessels, implying their similarity to respiratory trachaea of insects. Malphigi’s concept of cells seems different from that of Grew, in that he referred to them as utricules, or sacs, suggesting he believed they were filled with liquid. Of note, Malpighi described the formation of plant galls resulting from deposition of insect eggs, which was one early observation that argued against the ancient, pseudoscientific concept of spontaneous generation. (Harris, 1999)

1674 Antoni van Leeuwenhoek, it seems clear, came to view living matter as made of globules (cells, essentially), as he reports in Philosophical Transactions of the Royal Society: “I have divers times endeavored to see and to know, what parts the Blood is composed of; and at length I have observ’d taking some blood out of my own hand, that it consists of very small globuls driven through a Crystalline humidity of water…”, suggesting that similar globules meld to form hair.

Christiaan Huygens queried Oldenburg, the editor of the Transactions: “I should very much like to know what credence is given by your people to the observations of our Mr. Leeuwenhoek who turns everything into little balls.” (Harris, 1999)

1682 Nehemiah Grew’s The Anatomy of Plants was published, and his text makes it clear Grew thought the cells he was studying were more like bladders (or foam), forming through inflation. That suggested to Grew that the walls he observed were somewhat skeletal, and suggests to us that he viewed plant tissue as fenestrated, which would mean the “cells” were equivalent to pores. He applied the term parenchyma to the tissue, suggesting this is filler material, flesh (Harris, 1999)

1733 In Lyons, Jesuit Father Sarrabat set plant roots in the red juice from Phytolacca fruit and observed the colored liquid rising to leaf tips, and even stamen filaments. He noted the root cortex was red. This is considered the first example of vital staining. (Clark & Kasten, 1983)

1756 O. F. Müller described binary fission in Vibrio (Closterium) lunula, a microscopic green alga. (Harris, 1999)

1759 (1774 2nd ed) Kaspar Friedrich Wolff published Theoria generationis, explaining his concepts that the vessels (of plants) and fibers (animal cells) were secondary, beginning as cells or vesicles, something akin to Leeuwenhoek’s globules.

He may have envisioned them as originating through inflation, though eventually some would be filled with liquid. In studying development of a seed leaf (cotyledon), Wolff observed: “the young leaf arising from the seed turns out to be composed entirely of vesicles, and is patently devoid of fibers, vessels or grooves of any kind… They arise from a hitherto unadulterated, homogeneous, glassy substance, without any trace of vesicles or vessels.” Almost certainly, Wolff was examining the apical meristem, or an emerging leaf primordium, which would have been composed of such minuscule meristematic cells that he could not resolve more structure in the “glassy substance.” That would not have been a surprise, since he explains in reference to animal tissue: “its constituent parts [could] escape notice on account of their very smallness.” (Harris, 1999) Wolff’s ideas concerning embryology did not advance the science; he supported the homunculus concept (look it up) in each sperm. (Wikipedia, 2018)

1774 Bartholemew Corti published his observations of the fungus, Tremella (which he considered a plant), noting obvious circulation of fluid within the hyphae.   (Harris,1999)

1792 Luigi Galvani published De viribus Electricitatis, famous and grim studies of the effects of electricity on living tissues (in frogs). (Harris, 1999)

1802 Kurt Sprengel published his introduction to the study of plants (Anleitung zur Kenntnis der Gewächse), a book Harris suggests may be the publication that first suggested new cells could arise from granules or corpuscles inside existing cells. Decades would pass before researchers came to solid agreement that cells reproduce themselves through a division process (Harris, 1999) Note, in 1793, Sprengel published the earliest study of floral form and its relationship to pollination….

1804 Discovery of Inulin: “Valentin Rose (1762-1807) reported that the root of elecampane (Inula helenium) contained “a white material appearing very much like starch, but differing from it both in its principles and in its manner of action with other substances”. Rose found that after boiling the roots in water and leaving the decoction stand for several hours, a white powder precipitated, which looked very much like starch but differed from it both in its principlesand in its manner of action with other substances. This substance was soluble in cold water but readily soluble in boil- ing water producing a not quite transparent mucilagenous liquid. After some hours most of the solute reprecipitated as a compact white powder; addition of alcohol produced the same effect.” (Jaime Wisniak, 2016. “Henri-François Gaultier de Claubry”, Revista CENIC Ciencias Químicas, v 47(1), Versión Electrónica 2221-2442)

1805 In studying sections of Ranunculus ficaria, Gottfried R. Treviranus reported that living cells are separate and independent from one another: “The origin of the organization of living material is an aggregate of vesicles (i.e. cells), which have no connection with each other. From these vesicles all living bodies are formed, and all they contain eventually undergoes dissolution”   (Harris,1999)

1806 The Royal Society of Science of Gottingen (Konigliche Societat der Wissenschaft) organized a competition for essays on plant vessels (cells). Submissions by Link, Rudolf’s and Treviranus were accepted, and Link was awarded the prize. (Harris, 1999) (PS: the German naturalist Gottfried Reinhold Treviranus and the French scientist Lamarc independently in- troduced the term biology in 1802)

1807 As reported in his book Grundlehren der anatomie und physiologie der pflanzen, Heinrich Friedrich Link established the independent nature of plant cells through various studies and manipulations. He noted coloration versus lack of color in the cells of variegated plants. He studied the movement of cell contents once they were denatured with heat. Link, like his contemporary Ludolph Christian Traviranus, did not see direct evidence as to how cells might communicate or transfer materials to each other, but he imagined there could be invisible openings. As with others in this period, Link had no answer as to how new cells originate, nor a concept of nuclei. (Harris, 1999)

1811 Ludolph Christian Traviranus reported studies from 1803, in which he observed cyclosis (protoplasmic streaming) in Hydrodictyon utriculatum and Nitella flexilis. He was not aware of a report by Conti, from 1774, (“Microscopic observations on Tremella and on the circulation of fluid in an aqueous plant”) (Harris, 1999)

1812 Moldenhawer’s Beiträge zur Anatomie der Planzen, summarized nearly two decades of work, demonstrating that plant cells an be separated through macerating tissue in water. (Harris, 1999) Moldenhawer noted that stomata were formed by paired cells, and discussed the nature of tree rings.

1814   Following the discovery of iodine in 1811 by Bernard Courtois, Jean-Jacques Colin and Henri-François Gaultier de Claubry introduced iodine staining in Annales de chimie et de physique. Quoted from Wisniak, their study advanced methodically: “In the first part of their memoir they indicated they would describe their results using the three-tier classification of vegetable and animal substances suggested by Gay-Lussac and Thenard: (1) substances composed of carbon, hydrogen, and oxygen, in the ratio they are present in water plus the excess oxygen (that is, the acids); (2) substances composed of carbon, hydrogen, and oxygen, in the ratio they are present in water, that is, sugar, gums, starch, etc. (carbohydrates). This category also included animal substances containing nitrogen and hydrogen in the ratio present in ammonia (albumin, gelatin, fibrin, etc.); and (3) substances similar as those in the previous category but containing an excess of hydrogen (oils, camphors, etc.).”The second part of their work observed that: “mixing dry starch with dry iodine led to the immediate coloring of starch from blue to black, depending on its proportion in the mixture. This phenomenon was observed with starch of several origins, for example, from potatoes, salep, and the mucilage of the roots of marshmallow.

The coloration disappeared only when the mixture was heated to the temperature of decomposition of the vegetable matter: HI (iodohydric acid) vapors formed mixed with the product of the decomposition of the organic matter.” (Jaime Wisniak, 2016. “Henri-François Gaultier de Claubry”, Revista CENIC Ciencias Químicas, v 47(1), Versión Electrónica 2221- 2442)

1815 Dietrich Georg Kieser’s 1814 essay “Mémoire sur l’organisation de plantes” was awarded a prize offered by the Teylerian Society (Teyler’s Museum, Haarlem) for entries related to plant structure. In this same year, Kiefer published his text- book Elemente der Phytotomie, which provided an important summary of work to date. Kieser states that “plants are composed in large part of cells, which form a tissue,” with a contemporary but erroneous understanding that cells originate from globules suspended in plant sap. (Harris, 1999)

1823 Giovanni Battista Amici first observed growth of pollen tubes, in Portulaca. In 1846 Amici confirmed (studying orchids) that the embryo forms from an egg in the embryo sac, which is stimulated to seed production by presence of the tip of the pollen tube. This revelation had followed Brown’s suggestion the tubes were produced by the ovary, and Schleiden’s assertion that the tip of the pollen tube “becomes” the seed. (Johnson, 1915, History of the Discovery of Sexuality in Plants, G**gle Play)

1823, 1826 French zoologist Henri Milne-Edwards described animal cells as similar in shape and volume, in contrast to the better-known variety in size and shape of plant cells. He assumed that larger tissues were made of “globules, which might be called elementary, are perhaps themselves formed by still smaller corpuscles that our present methods of investigation do not permit us to see.” (Harris, 1999)

1824-1837 Henri Dutrochet (née du Trochet), commenting on the similarity of plants and animals in his 1837 Mémoires: “Life is one; the differences shown by its various phenomena, in all things that are alive, are not fundamental differences; if these phenomena are tracked down to their origins, the differences are seen to disappear and an admirable uniformity of plan is revealed.” In the words of H. Harris, Dutrochet is one of the first researchers who considered cells to be “physiological entities…, the basic units of metabolic exchange”. Dutrochet developed concepts of endosmosis and exosmosis (movement of molecules out of and into cells based on a concentration gradient). In Dutrochet’s words: “If one compares the extreme simplicity of this astonishing structure (the cell) with the extreme diversity of its innermost nature, it is clear that it constitutes the basic unit of the organized state; indeed, everything is ultimately derived from the cell.” Keep in mind that Robert Brown described the plant cell nucleus in 1831-1833, but animal cells were not as amenable to study  (and erythrocytes, which Leeuwenhoek had described, are enucleate), thus Dutrochet and his colleagues knew about globules or cells, but were unclear as to their origins or internal structure. (Harris,1999)

1825 Raspail (who introduced iodine to stain starch granules) insisted that starch grains are the progenitors of new cells (vesicles). In his 1825 publication (Développement de la fé- cule) Raspail states, in Latin: “Omnis cellula e cellula” (Every cell is derived from another cell), a proclamation normally attributed to Virchow. (Harris, 1999)

1830 German doctor Franz J. F. Meyen published his Phytoto- mie, in which he discussed the shapes of plant cells and his concept that those shapes were determined by mathematical laws. Meyen appreciated the homology of cells in algae as compared with those of flowering plants. A few years later, in 1837, Meyen published his Neues System der Pflanzen-Physiologie, remarking: “In the year 1832 M. Dumortier observed the multiplication of cells by means of true cell division…  this kind of cell multiplication by means of cell division was observed by C. Morten in Closteria(a Charophyte) and by H. Kohl in Conferva (Cladophora) glomerata. Nowadays, the number of such observations has greatly increased.” Indeed, referencing liverworts, he states: “the most striking demonstration is provided by spore formation in the genus Marchantia, where the evidence is compelling that cell multiplication does not take place in so-called mother cells, but by means of cell division as it does in other mosses and liverworts.” Though Meyer does not step away completely from other concepts of cell formation, he clearly advances the idea that cell division is significant. (Harris, 1999)

1830 Charles Moreno described binary cell division in Crucigenia, which he described as a new kind of microscopic plant (an alga) (Harris, 1999)

1831 Though not published until 1833, Robert Brown delivered his paper to London’s Royal Society, describing the aureole, or nucleus as he also called it, so commonly present in plant cells. (Harris, 1999) (see also: Sophie C. Ducker and R. Bruce Knox, 1985. “Pollen and Pollination: A Historical Review” Taxon, 34 (3 ): 401-419, International Association for Plant Taxonomy (IAPT) https://www.jstor.org/stable/1221207

1832 Bartheley Charles Dumortier published his observations of Conferva (Cladophora) aurea, explaining that cell division is binary (the cell divides in two) through creation of a midline partition and extension of the cell wall. He explicitly rejected models (such as ideas of Kieser and Treviranus) that involved cells created through growth of granules or internal partition- ing of existing cells. (Harris, 1999)

1833 François Vincent Raspail developed methods to freeze and section tissue, and devised a platinum spoon on which cells could be incinerated for analysis of the residue, reminding us he was truly one of the founders of cell chemistry. In Harris’s translation of Raspail’s research interests, they were: “Chemical and physiological experiments designed to explain not only the structure and development of the leaf, the trunk and the organs that are merely transformation of them, but also the structure and development of animal tissues.”   Paraphrasing Laplace, Raspail wrote (in translation): “Give me an organic vesicle endowed with life and I will give you back the whole of the organized world.” (Harris, 1999)

1833 Johannes Müller was appointed to a chair in Berlin, overseeing a lab that would turn out a series of influential students – Schwann, Henle, Remak, and Virchow. some “Discoverers” and others “Colonizers” (Harris, 1999, page 136)

1836 Valentin, an associate of Purkyně, and the first person to apply the term nucleus in relationship to animal cells, accepted a position in Bern, and thus became among the first Jewish scientists appointed as full professor at a German-speaking university. (Harris, 1999)

1837 Studying filamentous algae (Cladophora, Zygnema) as well as several seaweed, Hugo von Mohl confirmed that cells arise through binary fission. As had Dumortier, Mohl rejected earlier suggestions that new cells might originate from granules (such as plastids). Mohl’s publications were well-known, and thus he is typically given credit for discovery of binary fission. (Harris, 1999)

1837 Theodor Hartig was the first to characterize and name sieve tube elements. These are the living cells in phloem tissue that physically move photosynthate (sugars) from one location to another in a plant (from the site of production in a leaf to a sink such as a growing root, for example). (Wikipedia, 2015)

1837 In a lecture presented at the Society of German Naturalists and Doctors, Purkyně states, in reference to animals: “the basic cellular tissue is again clearly analogous to that of plants which, as is well known, is almost entirely compose of granules (Korner) or cells.” His presentation marks the time during which the word cell (zellen) was becoming the standard term for life’s units. (Harris, 1999)

1837 Carl Julius Fritsche published Ueber den Pollen, summarizing much of his extensive study of pollen grain structure, and coining the words intine and exine. (Ducker and Knox, 1985)

1838 In summary, from The Birth of the Cell, Harris: “This review of the most widely read textbooks of the day makes it clear that before 1838 the scientific community had no inkling of the ubiquity of cells in living forms. It was generally agreed that plants were largely composed of cells, and cells had indeed been seen in several animal tissues, but no one had suggested in print that plant and animal cells were homologous. Nor was there any agreed opinion about how cells were generated. Binary fission had been described, but its occurrence, when noted at all, was thought to be an exceptional mode of cell multiplication limited to certain lower forms of plant life. Nothing like binary fission had yet been observed in animal cells.” (Note that Abraham Trombley, in a 1744 letter to the Royal Society described longitudinal division in fresh water polyps). (Harris, 1999)

1839 Theodore Schwann’s acclaimed book, Microskopische Untersuchengen über die Uebereinstimmung in der Struktur und dem Wachsthum der Thiere in Pflanzen was published in Berlin. Schwann’s proposition: “The aim of the present treatise is to establish the intimate connection between the two kingdoms of the organic world by demonstrating the identity o the law governing the development of the elementary subunits of animals and plants.” Given credit as the beginning of current understanding of the Cell Doctrine, Schwann’s monograph is an effective but flawed compilation. He accepted concepts from the botanist Schleiden, which were outmoded and incorrect regarding initiation of new cells. Thus some of the very laws on which he based his understanding were incorrect. Schwann also glossed over priority and contributions of others to the consolidation of this idea, particularly disregarding the work of noted cell biologist Purkyně. In Harris’s words, Schwann was a Colonizer; he came from Mueller’s lab, where marketing tended toward bravado. (Harris,1999)

1843 Francois-Vincent Raspail, describing the independent activity of animal cells: “Each cell selects from the surrounding milieu, taking only what it needs. Cells have varied means of choice, resulting in different proportions of water, carbon and bases which enter into the composition of their walls.  It is easy to imagine that certain walls permit the passage of certain molecules… A cell is therefore a kind of laboratory within which all tissues organize and grow.” Note Harris’s translation refers to a cell “wall”, which remained the sole construct until the cell membrane was described and the cell wall was understood to be an external, non-living component of the plant cell. And, Harris states, Raspail had “no inkling of a cell nucleus.” (Harris,1999)

1844, 1846 Hugo von Mohl distinguished between plant sap and cellular content, which eliminated considerable confusion in the literature. In his later paper, Mohl proposed the word protoplasma for the fluid (or gel) that fills cells, a word use that had been introduced by Purkyně a few years earlier. Protoplasm quickly replaced earlier terminology. (Harris, 1999)

1844 Franz Unger (studying Campelia (Tradescantia) zanonia) confirmed binary cell division in flowering plants. (Harris, 1999)

1847 Reichard published observations (with nematode sperm development) that the nuclear envelope disappears in advance of cell division, and nuclei reappear in the daughter cells. Important and accurate, these observations still fall short of observing the consolidation of chromatin… (Harris,1999)

1848 Followed quickly with his 1849 monograph, Wilhelm Hofmeister illustrated and described formation of chromosomes during mitosis, first with Tradescantia, and subsequently in Passiflora coerulea and Pinus maritima. He also observed and accurately reported reductive division in meiosis of Psilotum. Hofmeister didn’t use the term chromosomes [see 1888], or express any deeper significance to these observations. (Harris, 1999)

1849 Heinrich Richard Göppert and Ferdinand Cohn, while studying Nitella flexilis, introduced cochineal-derived carmine staining techniques to plant microtechnique. “Of the natural dyes used by cytologist, none was more esteemed than carmine.”(Clark & Kasten, 1983)

1851 Elucidation, by Hofmeister, of alternation of generations in plants.

1856 The value of aniline dyes as biological stains became so apparent that new dyes were quickly adopted: Basic Fuchsin (1856), Safranin (Williams in 1859), Methyl violet (by Lauth in 1861), Aniline Blue and Sprit Blue (by Girard and deLalpe in 1861), Eosin (by Caro in 1871), Methyl Green (by Lauth ad Boubigne in 1871), Thionin (by Lauth in 1876), Methylene Blue (by Caro in 1876), Acid Fuchsin (by Caro in 1877), Orange G (by Baum in 1878), Sudan III (by Rumf and Garasche in 1879), and Azure B (by Bernthsen in 1885). (Clark & Kasten, 1983)

1859 Charles Darwin published On the origin of species by means of natural selection.  As explained by Darwin, evolution is a simple change in character of a population of either plants or animals. Circumstances governing the success of a population are not neutral, rather the environment favors certain characteristics, which creates a natural system of selection that can lead to changes in the makeup of a population. Gradual change in a population can lead to differences that qualify the population as a distinctive enough to become a new species – thus the “origin” of species. By identifying a mechanism that could lead to the diversity of life on earth, Darwin rewrote the book on relationships of plants and interpretations of plant adaptations. My favorite quotation from Origin: “We have seen that man by selection can certainly produce great results, and can adapt organic beings to his own uses, through the accumulation of slight but useful variations, given to him by the hand of nature. But Natural Selection as we shall hereafter see, is a power incessantly ready for action, and is as immeasurably superior to man’s feeble efforts, as the works of Nature are to those of Art.” (HNT)

1866 After nearly a decade of hybridizing peas and gathering data on patterns of inheritance, Gregor Mendel explained and published his basic understanding of the hereditary nature of variation between individuals in a population, including mathematical statements as to predictable assortment of characteristics. Mendel “applied the terms dominant and recessive to the tall and dwarf habits respectively” (Punnett, 1905). It is puzzling that Mendel’s works, though highly com- plementary to Darwin’s concepts, were not brought forth for general scientific discussion until 1900.

1872 Edmund Russow observed and described chromosomes (which he called rods, ‘Stabchen’) in sporangial development of the ferns Polypodim vulgare and Aspidium felix. (Harris, 1999)

1875 Edward Strasburger and Otto Butschli (studying nematodes, and later, chicks), working independently and yet collaboratively, confirmed the consolidation of nuclear material as chromosomes (not yet named) and a regular choreography of events in both plants and animals. (Harris, 1999)

1879 A word for nuclear divisions, karyokenisis, was intro- duced by W. Schleicher. (Harris, 1999)

1879 The term chromatin was introduced by Walther Fleming to describe nuclear condensations that yield what we later learned to call chromosomes. In this year, he also introduced the term mitosis. (Harris, 1999; Verga and Agarwal say it was 1882)

1879 Eduard Tangl reported connections between cells (now called plasmodesmata) in seed of the tropical liana Strychnos nux-vomica (the source of the poison strichnine).  Tangl’s observations were well-received, as contemporary botanists believed some order of connectivity would be discovered. Wilhelm Pfeffer (who elucidated the nature of osmotic pressure) was especially impressed, writing: “the continuity of the living substance is so essential (for correlative harmony in the whole plant) that it would be necessary to propose it if it were not already discovered.” (Piotr Köhler and Denis J. Carr, 2006. “Eduard Tangl (1848–1905) – discoverer of plasmodesmata” Huntia 12(2):169-172)

1880 Following up on his 1879 work with Salamanders and other animals (in which he employed the term “chromatin” for the nuclear threads that take up stain), Walther Flemming investigated Lilium croceum, in which he also observed “longitudinal splitting” of chromosomes. This ties into his insistence on indirect nuclear division as the norm (as contrasted with faulty observations that suggest the entire nucleus simply splits in half, rather than breaking down.) Though Flemming expressed no relationship between this form of duplication and the workings of inheritance, the understanding as to how chromosomes are duplicated proved to be a critical step in moving toward understanding of mechanisms of inheritance. (Harris,1999)

1882 Walther Fleming published Zellsubstanz, Korn, und Zelltheilung, in which he coined the slogan: Omnis nucleus e nucleo (that is, nuclei are only produced from other nuclei)… (Harris, 1999)

1883 Studying the parasitic nematode Ascaris, Edouard van Beneden clarified, once and for all, that nuclear material contributed through sperm and those from the egg remain discrete; they do not fuse together: “Thus there is no fusion between the male chromatin and the female chromatin at any stage of division… The elements of male origin and those of female origin are never fused together in a cleavage nucleus, and perhaps they remain distinct in all of the nuclei derived from them.” (Harris, 1999) A few decades later, researchers would come to realize that when chromosomes pair, they can swap segments (Researchers began to appreciate crossing in Thomas Hunt Morgan’s lab, see TL 1911)

1884 Terms in use today for the stages of mitosis (prophase, metaphase, anaphase, telophase) were introduced by Strasburger. In the same year, through studying fertilization in Orchis latifolia, Strasburger showed that the pollen nucleus
is forced out of the pollen tube into the egg sac, with little evidence of any accompanying cytoplasm. Observations such as this further enforced gathering realization that nuclear material is the source of heredity. (Harris, 1999)

1884 Studying the impact of various salt solutions on cell activity, Hugo de Vries confirmed that a cell membrane (internal to the cell wall) exists, which regulates the movement of water and solutes. He described earlier work and introduced the term plasmolysis to describe the shrinking of cell contents from the cell wall due to osmotic flow. (Harris,1999)

1885 Carl Rabl, studying Salamanders, demonstrated that chromosomes remained consistent in number and character. (Harris, 1999)

1888 Hanreich Wilhelm Gottfried Waldeyer-Harz proposed the word chromosome “to replace the previous miscellany of Stabchen, Shleifen, Faden (threads), and bayonets”. (Harris, 1999)

1888 Theodor Boveri, studying the parasitic nematode As- caris univalens (which has two chromosomes), demonstrated that the number and individual appearance of chromosomes persists through reproduction, which he expressed as the principle of ‘The Continuity of Chromosomes’. (Harris, 1999)

1895- 1890. Working with Spirogyra, Ernest Overton solidified observations by de Vries [1884] regarding regulation of osmotic balance across a cell membrane. (Harris, 1999)

1898 Carl Benda named mitochondria in Arch. Anal. Physiol 393-398 (Lars Ernster and Gottfried Schatz, 1981. “Mitochondria: a historical review” J Cell Biol.: 91(3): 227-255. PMCID: PMC2112799; PMID: 7033239 (http://doi.org/10.1083/jcb.91.3.227s

1901 Strasburger identified connections similar to those Tangl had described in 1879, creating the term plasmodesmata.

1902 Boveri, working with sea urchin eggs, demonstrated that individual (distinguishably different) chromosomes consistently correlate with specific heritable traits, a second principle he called ‘The Individuality of Chromosomes’ (Harris, 1999)

1902 William Bateson published Mendel’s Principles of Hered- ity – A Defense, in which he introduced many important terms and concepts… The words homozygous and heterozygous, homozygote and heterozygote, as well as allelomorph (from which we take the term allele) show up in this early exposition. (Original text available through Internet Archive = archive.org)

1902 Garrod, Archibald E. 1902. “The Incidence of Alkap- tonuria: A Study in Chemical Individuality” (Lancet, vol. ii, pp. 1616-1620.) In a strikingly modern and predictive publication, Garrod introduces compelling evidence (which, as with Mendel’s work, would be almost wholly ignored for decades) of the genetic basis for disease, based principally on his study of alkaptonuria. He states: “It has recently been pointed out by Bateson that the law of heredity discovered by Mendel offers a reasonable account of such phenomena. It asserts that as regards two mutually exclusive characters, one of which tends to be dominant and the other recessive, cross–bred organisms will produce germinal cells (gametes) each of which, as regards the characters in question, conforms to one or other of the pure ancestral types and is therefore incapable of transmitting the opposite character. When a recessive gamete meets one of the dominant type the resulting organ- ism (the zygote) will usually exhibit the dominant character whereas when two recessive gametes meet the recessive character will necessarily be manifested in the zygote. In the case of a rare recessive characteristic we may easily imagine that many generations may pass before the union of two reces- sive gametes takes place.”

1903 Wilhelm Johannsen introduced the terms phenotype and genotype as part of his discussion of pure lines in breeding. Abstract from D. Berry, “The plant breeding industry after pure line theory: Lessons from the National Institute of Agricultural Botany.” Stud Hist Philos Biol Biomed Sci. 2014 Jun;46:25-37. doi: 10.1016/j.shpsc.2014.02.006. E-pub 2014 Mar 17.

“In the early twentieth century, Wilhelm Johannsen proposed his pure line theory and the genotype/phenotype distinction, work that is prized as one of the most important founding contributions to genetics and Mendelian plant breeding. Most historians have already concluded that pure line theory did not change breeding practices directly. Instead, breeding became more orderly as a consequence of pure line theory, which structured breeding programmes and eliminated external heritable influences. This incremental change then explains how and why the large multinational seed companies that we know today were created; pure lines invited standardisation and economies of scale that the latter were designed to exploit. Rather than focus on breeding practice, this paper examines the plant varietal market itself. It focusses upon work conducted by the National Institute of Agricultural Botany (NIAB) during the interwar years, and in doing so demonstrates that, on the contrary, the pure line was actually only partially accepted by the industry. Moreover, claims that contradicted the logic of the pure line were not merely tolerated by the agricultural geneticists affiliated with NIAB, but were acknowledged and legitimised by them. The history of how and why the plant breeding industry was transformed remains to be written.” (See also:Roll-Hansen, 2009. “Sources of Wilhelm Johannsen’s genotype theory.” N J Hist Biol. 2009 Fall;42(3):457-93.)

1904 Friedrich Meves (“Über das Vorkommen von Mitochon- drien bzw. Chondromiten en Pflanzenzellen,” Ber Deutsch.

Bot. Ges, 22: 284-286) was the first to report plant mitochondria, while studying tapetal cells of Nymphaea alba anthers. (see W. C. Twiss, 1919. “A Study of Plastids and Mitochondria in Pressia and Corn” American Journal of Botany, 6(6) 217-234; Earl H. Newcomer, “Mitochondria in Plants,” 1940. Botanical Review 6(3):85-147 Though observed before 1850, mitochondria were not described as cell organelles until 1894, when Richard Altmann named them bioblasts. In 1898, Carl Benda suggested the term mitochondria. Philip Siekevitz came up with the description of mitochondria as the powerhouse of the cell in 1957. (Wikipedia)

1905 William Bateson, Edith Saunders, and Reginald Punnett, encountered evidence of gene linkage while repeating aspects of Mendel’s work with peas. (Genetic Linkage in Wikipedia, 2018) Full-blown exposition of this non-Mendelian behavior would come shortly, through work with fruit flies in Thomas Hunt Morgan’s lab at Columbia University in New York.

1905 First edition of Punnett’s Mendelism

1906 First edition of Robert Heath Lock’s Recent Progress in the Study of Variation, Heredity, and Evolution, which many consider the first genetics textbook. You will read that the term “Genetics” first appeared in print in William Bateson’s review of Lock’s book. [see A. W. F. Edwards, 2013. “Robert Heath Lock and His Textbook of Genetics, 1906.”Genetics. 2013 Jul; 194(3): 529–537.doi: 10.1534/genetics.113.151266, PMCID: PMC3697961, PMID: 23824968], but that is not accurate in the least.  For example, in 1893, Charles Bessey used the phrase “genetic relationship” in his address on “Evolution and Classification” to the American Association for the Advancement of Science, Section G (see their journal, v 42, page 238) I believe it’s a fairly short and insignificant distance between talking about genetic relationships and referring to a field of study as genetics….

1908 William Weinberg (Germany) and Henry Harvey (England) independently arrived at mathematical statements regarding changes in genetic make-up of populations. The Hardy-Weinberg Principle contends that relative abundance of differing alleles (genes) in a population will remain stable unless a force selects or directs change. [See 1931, Sewell Wright.]

1908 George Shull’s “The composition of a field of maize” “marked the beginning of the exploitation of heterosis in plant breeding, surely one of genetics’ greatest triumphs… In his 1908 paper, Shull reported that inbred lines of maize showed general deterioration in yield and vigor, but that hybrids between two inbreds immediately and completely recovered; in many cases their yield exceeded that of the varieties from which the inbreds were derived. Furthermore, they had a highly desirable uniformity. In a subsequent paper in 1909, he outlined the procedures that later became standard in corn-breeding programs ” James F. Crow, 1998. ‘90 Years Ago: The Beginning of Hybrid Maize’, Genetics 148(3):923-928 (see also Shull, G., 1908. The composition of a field of maize” Am. Breeders Assoc. Rep. 4: 296–301.)

1909 Correns work with the wonderful Four O’Clock (Mirabilis jalapa), which produces variegated leaves, provided early evidence for cytoplasmic inheritance (that defies the Mendelian odds because chloroplasts are normally inherited from the mother-plant and carry their own genetic maternal). Today, researchers have explained more about the nature of the gene iojap, which generated Correns’ results by im- pacting the physiology of chloroplasts.

1909 Boveri summarized modern understanding of Chromo- some biology: “At fertilization, these two ‘haploid’ nuclei are added together to make a diploid nucleus that now contains 2a, 2b and so on; and by the splitting of each chromosome and the regulated karyokenetic separation of the daughter chromosomes, this double series is inherited by both of the primary blastomeres. In the resulting resting nuclei the individual chromosomes are apparently destroyed. But we have the strongest of indications that, in the stroma of the resting nucleus, every one of the chromosomes that enters the nucleus survives as a well-defined region; and as the cell prepares for its next division this region again gives rise to the same chromosome (theory of the Individuality of the Chromosomes). In this way the two sets of chromosomes brought together at fertilization are inherited by all the cells of the new individual. It is only in the germinal cells that the so-called reduction division converts the double series into a single one. Out of the diploid state, the haploid is once again generated.” (Harris translation, 1999)

1909 Frans Alfons Janssens published an article, “La théorie de la Chiasmatypie. Nouvelle interprétation des cinèses de maturation” presenting the idea of crossing over (which he called chiasmotypie) – a proposal that encountered long-term resistance . (Koszul R1, Meselson M, Van Doninck K, Vanden- haute J, Zickler D., 2012. “The centenary of Janssens’s chiasmatype theory” Genetics. , 191(2):309-17. doi: 10.1534/genetics.112.139733.

1909 Wilhelm Johannsen popularized the term gene.

1909 Thomas Hunt Morgan and his lab team opened a major thrust in genetic research when (after nearly two years of in- vestigation) they isolated workable mutations in populations of Drosophila melanogaster (fruit flies) they were studying at Columbia University. Simple to raise and easy to anesthetize, with a generation time of 10 days, these flies became the source of many great advances in our understanding of genetics and cell biology. (Harris, 1999)

1911 Punnett’s third edition of Mendelism included full-out displays of the notoriously-useful Punnett squares, learned by every student of biology.

1911 In Thomas Hunt Morgan’s lab, Alfred Sturtevant was achieving success in mapping certain fruit fly genes, explaining both linkage and crossing over. His work was first published in 1913. [Lobo, I. & K. Shaw, (2008) “Thomas Hunt Morgan, genetic recombination, and gene mapping”. Nature Education 1(1):205]

1913 – Eleanor Carothers documented independent assortment of chromosomes during meiosis.

1915 – Mathematician Ronald Fisher demonstrated that a small number of genes could interact to yield a finely-tuned continuum of variation (it pencils out).

1918 Donald Jones published “The effects of inbreeding and cross-breeding up0n development” (Jones, D. F., Connecticut Agric. Exp. Stn. Bull. 207), in which he proposed the “double cross” system, “a procedure that spread out the controlled hybridizing process over an extra generation and permitted tremendous increases in seed production.” (Jensen, inFrey, 1994)

1919 The publication of Inbreeding and Outbreeding by E. M. East and D. F. Jones gave scientific underpinnings to corn breeding and introduced Jones’s system of double crossing through the use of four inbred lines. This work, fostered by the US Experiment Station system, was one of the most significant early accomplishments of modern agricultural science. (Rasmussen, 1960)

1922 Göte Turreson published two significant articles in volume 3 of the journal Hereditas: “The species and variety as ecological units” and “The genotypical response of the plant species to the habitat.” In these publications, Turreson added the term ecotype and others to our working vocabulary.

1922 Edgar Anderson began work in St. Louis, MO as “Geneti- cist to the Garden” (heading Missouri Botanical Garden’s School of Gardening) and professor at Washington University. Anderson would quickly become one of the principle figures in development of biosystematics. “His first biosystematic project was a look at the species problem in Iris. His 1928 paper took up the species problem concretely by looking at populations of two closely related yet distinct species of iris and allowed Anderson to test the relative importance of hybridization and mutations as sources of the variation on which natural selection works “ (Kim Kleinman, 2009. “Biosystematics and the Origin of Species: Edgar Anderson, W. H. Camp, and the Evolutionary Synthesis”, Transactions of the American Philosophical Society, New Series, Vol. 99(1) 73-91, in Descended from Darwin: Insights into the History of Evolutionary Studies, 1900-1970 Stable URL: https://www.jstor.org/stable/27757425

1923 Accompanied by a microscope demonstration, Robert Feulgen reported his “nucleal reaction” and “nucleal staining” to the 8th German Physiology Congress, which met in Türbin- gen. Feulgen had successfully used staining procedures to lo- calize differing components of nucleic acids – aldehyde groups and pentose components, now termed the Feulgen Reaction, a vibrant red-violet stain for DNA. The Feulgen reaction is considered the first “end-point type reaction” – which would brand Robert Feulgen as “the first modern histochemist.” Beyond introducing an important staining technique, this demonstration eliminated previously-existing ideas that plant DNA differed from animal DNA. In comments from a 1956 presentation by Kurt Felix (who had attended the 1923 presentation): “In all preparations the nuclei were stained red-violet.  The exciting finding for us was the reaction of not only the nuclei of animal cells, but rather also those of plant cells. With this demonstration, the difference between plant and animal nucleic acids ceased to exist.  All cells contained in their nuclei the same kind of nucleic acid which we refer to today as deoxyribonucleic acid or DNA.” (Clark & Kasten, 1983)

1926 John Belling published “The iron-acetocarmine method of fixing and staining chromosomes” in Biol. Bulletin 50:1160-162, a modified version of a technique he had introduced five years earlier in American Naturalist. Studying chromosomes in a range of plants (Canna, Cypripedium, Hemerocallis, and many other monocots), Belling’s new technique improved acetocarmine staining by adding iron (even simply using a rusty probe will work), which generated stronger differentiation between chromosomes and cytoplasm. (George Clark and Frederick Kasten, 1983)

1927 The first patent for a Scanning Electron Microscope (SEM) was filed in Germany, but decades would pass before workable instruments were commercially available (Cambridge Scientific Instrument Company, 1965). Those instruments gave magnifications of 10 to 200,000 times life size with magnificent depth of field, 500 times that of light microscopy. The earliest botanical observations using SEM were published between 1965 and 1970, with large numbers of applications and publications appearing over the next decade. Initially, the technique proved most useful for surface structure, but anatomists quickly worked this into their research.. Margaret Y. Stant , 1973. “The Role of the Scanning Electron Microscope in Plant Anatomy” Kew Bulletin, Vol. 28, No. 1 (1973), pp. 105-115, Source JSTOR Kew Stable URL: http://www.jstor.org/stable/4117068

1927 Using light microscopy, C. Zirkle demonstrated that chlo- roplasts develop from clear proplastids. (L. Andrew Staehelin, 2005.  “Chloroplast structure: from chlorophyll granules to supra-molecular architecture of thylakoid membranes”, pp 717-728 in Discoveries inPhotosynthesis

1928 Following similar work with Drosophila, Stadler used X- rays to produce mutations in corn (Zea mays). ©.( Zirkle in Ewan, 1969)

1928 – Frederich Griffith published proof of transformation, a natural process through which genetic material from one organism is inserted into the genome of another.

1930 Münch applied the terms apoplast and symplast to designate continuity of cytoplasmic content (the symplast) as opposed to the extracellular matrix (the apoplast).

1931 Sewell Wright presented the first clear concept of Genetic Drift (Wright, 1931, “Statistical Theory of Evolution”, Journal of the American Statistical Association, 26(173, Supplement): 201–208: “It has seemed to me that another factor should be much more important in keeping the system of gene frequencies from settling into equilibrium. This is the effect of random sampling in a breeding population of limited size. The gene frequencies of one generation may be expected to differ a little from those of the preceding merely bychance. In the course of generations this may bring about important changes, although the farther the drift from the theoretical equilibrium, the greater will be the pressure toward return.” Direct Source: Stanford Encyclopedia of Philosophy, “Genetic Drift” First published Sep 15, 2016)

1937 Robin Hill conclusively demonstrated that oxygen generated during photosynthesis (now called the Hill Reaction) does not require the presence of carbon dioxide. Hill’s studies furthered work by T. W. Englemann, who in 1883 had demon- strated that chloroplasts of the alga Spirogyagenerate oxygen most actively when exposed to red and blue light. By 1941 C.B. van Niel, Samuel Ruben, and co-workers had demonstrated that oxygen liberated during photosynthesis comes from the splitting of water. (McDonald, 2003)

1939 The first commercial Transmission Electron Microscope (TEM) was available. Work on this concept began a decade earlier with efforts of Ernst Ruska and Max Knoll. Ruska was awarded the Nobel Prize in 1986 for his role in TEM.

1943 Henry Wallace (owner of Pioneer Hi-Bred and US Vice- President) and Marte Gomez (Mexico’s Minister of Agriculture) coordinated with Raymond Fosdick and the Rockefeller Foundation to establish programs to improve corn and wheat production. The Mexican government established an Office of Special Studies (OSS). In 1941, anticipating this program, Richard Bradfield (Cornell, soil science), Paul Mangelsdorf (Harvard, botany), and Elvin Stakman (Minnesota) constituted the review committee endorsing creation of the Rockefeller-financed Mexican Agricultural program (MAP). Jacob Harrar and Norman Borlaug were among the founding scientists. MAP was the precursor to CIMMYT (Centro Internacional de Mejoramiento de Maíz y Trigo), the International Maize and Wheat Improvement Center. (Dworkin, 2009; Cotter, 2003; Christensen, 1984; CIMMYT website, 2017)

1943 Building on their own work and recent reports of many scientists, Hugh Davson and James Danielli formulated the “paucimolecular membrane model,” which predicts a lipid- protein-lipid trilaminate structure for membranes. By 1959, using newly available fixatives, J. David Robertson had produced electron micrographs that gave physical evidence of the tri-lamellar structure. This work underpins the “fluid mosaic model” proposed in 1972 by Singer and Nicholson, which resolves issues of stability. (Wayne,2009)

1944 Oswald Avery had directed his research to examine Frederick Griffith’s remarkable work, demonstrating that some physical essence in killed bacteria could be taken in by other bacteria and result in genetic change, an alteration Griffith called transformation. In a series of experiments that involved careful purifications of various fractions, Avery with his colleagues Colin MacLeod and Maclyn McCarty, deter- mined that the material effecting the change was Deoxyribose nucleic acid (DNA). Their work partially confirmed that genetic information is somehow stored in DNA. (Mukherjee, 2016) [See Hershey and Chase, 1952]

1945 Through their studies of limiting factors in growth of bread mold, Neurospora crassa, George Beadle and Edward Tatum noted the impact of mutations that meant individual enzymes were not functional. Beadle and Tatum were able to confirm that a gene provides instructions for a particular protein, advancing understanding of genetics through explaining how genetic information was translated into form and function in a cell. (Mukherjee, 2016)

1945 See Kevin Porter, 1953, Endoplasmic Reticulum

1946 Marion Parker, Sterling Hendricks, Harry Borthwick, and Fritz Went published “Spectral sensitivities for leaf and stem growth of etiolated pea seedlings and their similarity to action spectra for photoperiodism” (American Journal of Bot- any, 35:194-204), explaining that Red light impacts plant growth, inciting new lines of investigation and causing researchers in photoperiodism to refurbish their labs with green filters.  Previously, labs had followed protocols similar to those of black and white photography, using red “safe light” to illuminate workspaces. (Sage,1992)

1950 While conducting research at Brooklyn Botanic Garden, plant virus researcher Myron Kendall Brakke reported refinements in his development of density gradient centrifugation, a procedure that became basic for purifying virus samples. From the National Academy of Sciences: “Brakke’s early work … culminated in a landmark contribution to science: the invention of density-gradient centrifugation, which he used for the first time to purify potato yellow-dwarf virus. This technique provided an unparalleled capacity to purify viruses, separate nucleic acids and proteins, and fractionate cellular organelles. In his groundbreaking paper on density-gradient centrifugation in the Journal of the American Chemical Society, Brakke reported that the basic procedure could be modified for application to many different problems involving particles and large molecules of either biological or non-biological origin.” Yet, the utility of Brakke’s density- gradient centrifugation invention as a “separation procedure” and “as a criterion of purity, or as a technique for measuring densities of particles or large molecules,” did not become widely applied for nearly 10 years. Of course, ultimately sucrose density-gradient centrifugation became the most commonly used tool for a wide range of biological science applications and was key to the development of modern virology and molecular biology. Indeed, many advances in biology and the biomedical fields would not have been possible without this technique. By the latter half of the 20th cen- tury, density-gradient centrifugation was routinely used in nearly every biochemistry, molecular biology, cell biology, and virology laboratory in the world. Thus, Brakke’s novel development provided the foundation for a more profound understanding of disease agents, and the synthesis and struc- ture of proteins and nucleic acids.“ (National Academy of Sci- ences, “Myron Kendall Brakke 1921–2007 , A Biographical Memoir” by  Karen-Beth G. Scholthof, Andrew O. Jackson, and James L.Vanetten.

1951, 1953 Using autoradiography to study nutrient uptake by cells in the roots of beans, Alma Howard and Stephen R. Pelc defined the cell cycle (“Synthesis of nucleoprotein in bean root cells”Nature167)   A Quote From: Joseph G. Dubrovsky & Victor B. Ivanov, 2003. “Celebrating 50 years of the cell cycle” Nature 426 (759) “Howard and Pelc were the first to ascribe a timeframe to cellular life and they proposed the existence of four periods in the cell cycle: a period of cell division, the pre-S-phase (called G1), the S-phase (a period of DNA synthesis) and period G2, or the pre-mitotic period. The concept of the cell cycle was born.”

1952 Working at the Carnegie Institution, through studying insertion of isotope-labelled phage DNA in bacteria, Alfred Hershey and Martha Chase provided strong evidence that DNA is the material that holds genetic information in chromosomes.

1953 James Watson and Francis Crick published their double helix model explaining the physical structure of the DNA molecule.

1953 Kevin Porter reported the presence of a cytoplasmic network which he named endoplasmic reticulum (ER). This work was follow-up to a 1945 report of transmission electron microscopy by authors Keith Porter, Albert Claude, and Ernest Fullam, in which they noted observations of a “lacelike reticulum…, possibly the homologue of kinoplasm.” Because the 1945 article focused on techniques for TEM study of tissue culture cells, concern was expressed that the reticulum could be an artifact of specimen preparation. In his 1953 follow-up study, Porter confirmed this network and applied the name. (“A Study of Tissue Culture Cells by Electron Microscopy – Methods and Preliminary Observations,” J Exp Med. 1945 Mar 1; 81(3): 233–246. PMCID: PMC2135493; PMID: 19871454) (Kevin Porter, 1953. “Observations on a submicro- scopic basophilic component of cytoplasm.” J Exp Med. 97(5):727-50. [Also See: TL 1895, Garnier]

1955 Carlos Miller and colleagues described a plant hormone (derived from herring sperm) they named kinetin, which is involved in promotion of cell division (cytokinesis). In 1961, Miller described zeatin, the first named naturally-occurring plant cytokinin. This work grew from earlier studies on plant callus formation and cell-division by Folke Skoog and J. R. Jablonski. Before their work, Johannes van Overbeek had studied the impact of coconut milk on cell division in culture media. (University of Indiana website; Wikipedia, 2018; His tory of Cytokinins, website of the International Plant Growth Substances Association, 2018) [See TL 1913, 1961]

1958 – Francis Crick summarized what had become the Central Dogma of Molecular Biology: DNA makes RNA, RNA makes Protein, There is no going back. Protein cannot reverse-build RNA.

1959 Arthur Parde, François Jacob, and Jacques Monod, investigated changes in E. coli physiology that allowed the cells to switch from using glucose as an energy source to using lactose. Their study indicated that genetic activity is managed, or operated, turned on and off in cells, through allied genes the authors christened as operons.

1961 François Jacob and Sydney Brenner carried much of the water in explaining how Messenger RNA functions to transcribe information held by DNA molecular sequences into actionable templates from which proteins could be constructed. (Mukherjee, 2016)

1961 Wilhelm Minke applied the term thylakoidto the stacked, sac-like membranes that constitute the grana of chloroplasts… From Friederike Koenig and George H. Schmid, 2009. “Wilhelm Menke (1910–2007): a pioneer in chloro- plast structure” Photosynthesis Research 99(2) 81–84: “Having had already seen lamellar structures in chloroplasts from Nicotiana, Spinacia and Aspidistra in the laboratory of Manfred von Ardenne in 1940 and also in Anthoceros before World War II, he finally understood the inner structure of the chloroplast as a system of stacked and unstacked flattened vesicles surrounded by a membrane made of proteins and—besides pigments—lipids, mainly galactolipids,… He called them thylakoids, a Greek term for “sac-like” δνλαχοειδής. The original publication is in German (Menke 1961, translation in Gunning et al. 2006); however, many authors cite his review in this context, namely the 1962 article in Annual Review of Plant Physiology.”

1964 Sipra Guha (Mukherjee) and Satish Chandra Maheshwari published the first of two significant papers on their work with haploid embryos derived from Datura anthers. (“In vitro production of embryos from anthers of Datura”, Nature 204:4977; “Cell division and differentiation of embryos in the pollen grains of Datura in vitro”, Nature 212:97-98) From Wikipedia, 2018: The scientists developed “a new high-speed culture technique for producing homozygous pure lines of haploid plants which is now in practice for crop improvement and for commercial production of horticultural and ornamental plants”

1965 – Work in various labs resolved the “genetic code” – confirming how all combinations of the five “canonical” nucleobases correlate to amino acids.

1965Yoshiyuki Takasaki and Osamu Tanabe (working at the Japanese Fermentation Institute) developed a stable process to convert glucose to fructose. The tantalizing promise of that conversion had been the holy grail of the corn syrup industry. By 1967, Clinton Corn Processing Company had licensed rights to this enzyme for the US, and their scientists worked out kinks to industrializetheprocess.   (Folsom, Botany of Sugars, in A Botanical Reader)

1967 . “On the origin of mitosing cells” (Journal of Theoretical Biology. 14 (3): 225–274) was published by Lynn Sagan (Margulis). Her thesis re-popularized century-old ideas that cellu- lar organelles, such as mitochondria and chloroplasts, origi- nated as independent organisms, and are “symbiotic” compo- nents of contemporary cells. Andreas Schimper had noted the similarities between algae (Cyanobacteria) and plastids in 1883, as had Konstantin Mereschkowski in 1910. (see https://theendosymbiotichypothesis.wordpress.com/; see also Schimper, “Über die Entwicklung der Chlorophyllkörner und Farbkörper”. Bot. Zeitung. 41:105-…162)

1968 Studying chloroplasts of tobacco, K. K. Tewari and S. G. Wildman demonstrated the presence of plastid DNA. This followed work by H. Ris and W. Plaut in 1962 reporting DNA- like material in chloroplasts of the alga Chlamydomonas. (McDonald, 2003)

1969 Mary Lou Pardue and Joseph G. Gall published their arti- cle “Molecular Hybridization of Radioactive DNA to the DNA of Cytological Preparations”, in Proceedings of the National of Academy of Science/ From the Abstract: “A method is presented for detecting the cellular location of specific DNA fractions. The technique involves the hybridization of a radioac- tive test DNA in solution to the stationary DNA of a cytological preparation. Sites of DNA binding are then detected by autoradiography. Experiments with DNA of the toad Xenopus are described.” This work describes use of easily-visible fluorescent markers, i.e. FISH, which led to major advances in genetic and genomic studies.

1972 Jonathan Singer (Seymour Jonathan Singer) and Garth L. Nicholson described their “Fluid Mosaic Model” for cell membrane structure, built on the evolving tri-lamellar concept of a lipid bilayer, with embedded proteins, a dynamic sandwiching of lipids and proteins that allow for movement and embedding of many other kinds of ions, atoms, and molecules.

1973 – Herb Boyer and Stanley Cohen succeeded in the first successful artificial transformation (transforming the genome of an organism by inserting foreign genes). A year later, Cohen’s lab announced they had transferred a frog gene into a bacterium.

1977 – Biochemist Frederick Sanger published the first sequenced genome, that of a virus.

1978 – Ed Lewis and his team, working with fruit fly mutants, demonstrated that activation of genes is managed by master- regulatory effector genes.

1980 In their ruling on Diamond v. Chakrabarty, the US Supreme Court determined that genetically-altered life forms could be awarded patents. From Wikipedia, 2018: “After (Ananda Mohran) Chakrabarty had appealed his patent’s initial rejection, the Court of Customs and Patent Appeals had reversed in his favor, stating that “the fact that microorganisms are alive is without legal significance to the patent law”. In response, Sydney Diamond, Commissioner of Patents and Trademarks, decided to take this case to the Supreme Court. Diamond had two arguments which were not well received by the court. The first called the existence of the 1930 Plant Patent Act and the 1970 Plant Variety Act to suggest that there is a congressional understanding about the terms ‘manufacture’ and ‘composition of matter’ not referring to living things. The second was that microorganisms cannot qualify as patentable subject matter until Congress authorizes such protection since genetic technology was unforeseen when Title 35 U.S.C. 101 was first enacted.”

1982 The first genetically engineered crop was developed at Washington University in St. Louis, Missouri. By 1994 the Flavr-Savr tomato became the first such plant approved for commercial marketing. The Flavr-Savr tomato was designed for slow fruit ripening and increased shop life. (Levetin & McMahon, 1996)

1983 Kary B. Mullis devised the polymerase chain reaction, a system to replicate large quantities of DNA from a small initial sample. The ability to create a large sample of DNA for testing and study had extraordinary impact on various fields of study, from areas of paleobiology to forensic analysis. (Cobb & Goldwhite, 1995)

1983 Barbara McClintock received the Nobel Prize for her work with the complex color patterns of Indian corn, studies that revealed moveable genetic elements termed “jumping genes.”

1983 Agrobacterium fabrum (A. tumefaceins) was successfully used for genetic transformation of plants (in tobacco) by P. Zambryskit, H. Joost, C. Genetellol, J. Leemans, M. Van Montagu and J. Schell. See their publication. “Ti plasmid vector for the introduction of DNA into plant cells without alteration of their normal regeneration capacity” The EMBO Journal 2(12): 2143-2150: “The vector pGV3850 makes use of the natural transfer properties of the Ti plasmid; only those genes which interfere with normal plant differentiation have been removed. Thus, the most important aspect of pGV3850-transformed cells is their capacity to regenerate into complete plants. These plants can be derived from single cell and the regeneration process itself is extremely simple, requiring only minor changes in tissue culture conditions….. evidence has been presented that the Ti vector has evolved to a point where it is ready to be used to genetically engineer whole plants; it remains for us to turn our efforts toward the isolation of particular genes whose expression we wish to study.”

1987 Richard A. Jefferson published his GUS reporter gene system, which he had already shared extensively in an effort to support open sources for techniques. Jefferson’s technique has been widely adapted and utilized in plant transformation. The article, “Assaying chimeric genes in plants: The GUS gene fusion system”. Plant Molecular Biology Reporter. 5 (4): 387-405, is heavily cited. GUS is the symbol for the gene that codes forglucuronidase.

1987 Snowdrop lectin (GNA – Galanthus nivalis agglutinin) was brought to the attention of researchers through Els J.M Van Damme, Anthony. K Allen, and Willy J. Peumans, introducing a new agglutinin that might have potential medical value, but also would prove toxic to various insects, such as rice, sugarcane, papaya, potato, tomato, etc. Over the next decade, many distant relatives of Galanthus would be investigated, the structures and isoforms described, and genetic sequences made available for transgenic work. (Van Damme, Allen, & Peumans, 1987. “Isolation and characterization of a lectin with exclusive specificity towards mannose from snowdrop”, (Galanthus nivalis) bulbs. FEBS Letters 215, 140-144: “GNA represents apparently a new type of plant lectin with a unique carbohydrate-binding specificity.  Since this lectin can easily be isolated in reasonable amounts from readily available material it can be of great potential use as a biochemical tool.” Since that publication, genetic code for Snowdrop lectin has been introduced to various crops in order to reduce insect damage. https://febs.onlinelibrary.wiley.com/doi/epdf/10.1016/0014-5793%2887%2980129-1

1996 Monsanto introduced Roundup Ready soybean seed, the first genetically modified herbicide tolerant agricultural crop.

2000 Ten years after the US National Science Foundation selected Arabidopsis thaliana as the plant study organism for studies to elucidate the entire genetic sequence, and following four years of intense research in laboratories (at a cost of over $70 million), researchers announced the project was complete. The sequence of the approximately 120 million nucleotides (about 25,000 genes) that constitute the DNA of this plant was now known, the first plant genome to be fully sequenced. (Chamovitz, 2012)

2001 Genetically-modified (GM, i.e. transgenic) crop plants had clearly become mainstream, highlighted through reassessment this year by the US Environmental Protection Agency, reaching the conclusion that Bt cotton and Bt corn did not pose significant environmental risk for the environment or for human health. In 2001, Bt white corn was planted in South Africa for basic human subsistence (direct consumption) for the first time (previously, all GM maize had been used for animal food). By 2002, 6.8 million hectares had been planted to Bt cotton worldwide (12% of the world’s production.)   (Thomson, 2007) [Bt is the abbreviation for Bacillus thuringiensis, a soil-living bacterium. Bt produces what compounds called crystal proteins, abbreviated as Cry proteins, that are toxic to insect larvae, and are the active compounds in Bt pesticides. Companies have modified crop plants genetically by inserting the Cry genes, which cause the engineered crop plants to produce the toxin.]

2006 Researchers (G. A. Tuskan, et al) published a draft ge- nomic sequence of a selected Populus trichocarpa female specimen (Nisqually-1), in Science, the first woody plant to be sequenced.

2012 The Tomato Genome Consortium of researchers pub- lished the first complete genome of tomato (inbred cultivar ‘Heinz 1706’)

2012 Jennifer Doudna (UC Berkeley) and Emmanuela Char- pentier (Max Planck Institute) proved that CRISPR technology could be targeted for gene editing.

2013 Trials of “Golden Rice” produced through genetic engineering at the International Rice Research Institute (in the Philippines) were destroyed by anti-GMO forces. Rice is made “golden” through addition of genes that enable the rice to generate beta-carotenes, which are precursors to Vitamin A in humandiets.

Additional References:

Judson, Horace Freeland, 2013 (1996 Expanded) COMMEMORATIVE EDITION. The Eighth Day of Creation: Makers of the Revolution in Biology, Cold Spring Harbor Laboratory Press, New York, ISBN 978-0-879694-78-4 (Electronic Book). A remarkable document and must-read for those interested in the history of molecular biology, the Commemorative Edition follows the death of author Judson in 2011, and includes a forward by John Inglis, Executive Director of the Cold Spring Harbor Laboratory Press, Judson’s obituary, and a Reminiscence by the author’s daughter Olivia Judson.

Ducker, Sophie C. and R. Bruce Knox, 1985. “Pollen and Pollination: A Historical Review,” Taxon34(3): 401-419.

Frey, Kenneth J., 1994. Historical Perspectives in Plant Science, Iowa State University Press, Ames, ISBN 0-8138-2284- X, 205 pp.

A few resources to access:

Crow-Dove Perspectives: The Perspectives column was initiated in 1987 when Jan Drake, Editor-in-Chief of GENETICS, invited Jim Crow and William Dove to serve as coeditors of “Anecdotal, Historical, and Critical Commentaries.” SEE: William F. Dove, 2016. “Weaving a Tapestry from Threads Spun by Geneticists: The Series Perspectives on Genetics, 1987– 2008” Genetics 203(3): 1011-1022; https://doi.org/10.1534/genetics.116.191155