This is a glossary of terms that appear in Mendel's paper and other areas of MendelWeb. It is not meant to be exhaustive, and is aimed primarily at students in secondary and undergraduate schools.

The glossary is arranged alphabetically. Although you may find many of the terms familiar, the definitions and explanations frequently raise issues of translation and etymology, and contain links to Mendel's original text, to other documents in MendelWeb, and to resources throughout the World Wide Web. Please send corrections and suggestions to

The glossary is still under construction.

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1. to reconcile or bring into harmony with. 2. to make room for, or allow for, or to become adjusted to. 3. to adapt to or hold comfortably. From the Latin commodus, fit or fitting.

This is a peculiar translation of the German word vermitteln which in modern German means to mediate or to act as a mediator. But even the term "mediated" expresses poorly what Mendel is talking about here; he is describing an alteration or transformation in the fertilized egg of the hybrid that results in that hybrid behaving like one of the constant (or parental) forms found in Pisum. That is, unlike the pea hybrids that produce different kinds of pollen and egg cells, the "constant hybrids" discussed here produce only one sort of cell which results in the production of only those hybrids (rather than in a combination of hybrid and constant forms).

1. to advance or bring forward as proof, or as an argument. 2. to cite as evidence, proof, or as a means of proof in an argument. 3. to cite or bring forward as a reason or argument. From the Latin adducere, to lead to.

In the English version "Die aufgestellte Ansicht..." is translated as "The theory adduced...," which adds formality, and perhaps a more scientistic feeling to Mendel's original phrase. A more accurate translation might be "The view put forward.." Note that Mendel uses the word theoretischem only once in the paper; where "theory" appears in the translation it is often a rendering of words more accurately translated as "assumption" (e.g. Annahme).

1. conforming exactly to the truth, or to a standard. 2. careful, without error. Accurate comes from the Latin accuratus, done with care. From the Latin accurare to take care or to take pains with.

1. to provide, or make available. 2. to produce, or supply. From the Middle English aforthen, to provide or suffice.

albumen (see also endosperm and cotyledon)
1. the substance found in many seeds between the skin and the germ, usually the edible part of the seed 2. the nutritive material stored within the seed, usually surrounding the embryo though not within the embryo. 3. the nutritive matter in the seed used by the young plant until it develops roots and leaves. 4. egg-white. From the Latin word for egg-white, which is derived from the Latin albus, white.

Technically, Mendel's use of "albumen" and "endosperm" is inaccurate, because peas possess neither an albumen nor an endosperm. When Mendel used these terms he was referring to the cotyledons.

1. a flowering plant; a plant whose egg cells are enclosed in an ovary. Opposed to a gymnosperm, a plant whose seeds are not contained in an ovary (e.g. an evergreen). From the Greek aggeion, vessel, an sperm, seed; gymnosperm from gumnos, naked.

1. the upper parts of the stamen in which the pollen is produced, either in a single pollen sac or in groups of these sacs. 2. the terminal portion of the stamen of a flowering plant, containing pollen. From the Greek anthos, flower, via the modern Latin anthera, referring to the medicine extracted from flowers.

Common Columbine drawing Aquilegia
1. a genus of poisonous perennial herbs belonging to the buttercup family. 2. a genus of plants, often blue-flowered, sometimes called Columbines. 3. any of various perennial herbs of the genus Aquilegia, having showy flowers with petals that have long hollow spurs. 4. Several of the 70 known species of Aquilegia are cultivated for their flowers, which commonly have five tubular petals, five spurs, and more than twelve stamens.

Columbine comes from the Latin columbinus, dove-like, apparently referring to the resemblance between the inverted flower and a cluster of doves.

artificial crossing, artificial fertilization
1. the human application of pollen cells from one organism to the egg cells of another, or visa versa. 2. crossing two organisms by hand, or by other technological means, as opposed to allowing them to cross naturally. 3, the use of human artifice or technique to accomplish sexual reproduction between organisms.

1, to find out or get to know as a fact. 2. to discover with certainty, through investigation or examination. From the Middle English acertainen, to inform, and of course the Latin certain.

1. the absorption or taking into, either in the body (e.g. food) or the mind (e.g. information). 2. the process of making or becoming like. From the Latin similis, like.

Here Mendel seems to be speculating about a mechanism by which a hybrid embryo could be transformed such that one would not observe the return of parental forms in subsequent generations (as one observes in Pisum). Mendel used the term Stoffaufnahme, which can be translated literally as "substance admission".

1. a combination or connection, usually for a particular purpose or function. 2. an organized group of people who have an interest, or a number of interests, in common. 3. a connection between ideas, thoughts, or sensations. From the Latin socius, accompanying, or acting together.

We know that Mendel understood that some of the characteristics of his experimental plants were regularly connected with one another, in the way they were inherited. He described these characters alternately as "associated" and "constantly correlated"; and today we would describe the associated or regularly connected characteristics as "linked" genetically. The experiments reported in the paper, however, focus on seven characteristics that did not exhibit such an association or constant correlation.

1. something accepted as true, without proof. 2. something assumed to be the case.

1. the usual amount or extent. 2. the amount obtained by dividing the sum of a series of values by the number of values in the sample or set. 3. the intermediate value between extremes, evaluated on some sort of scale. 4. (legal terminology [archaic]) the distribution of loss that results from damage to a ship's cargo. Related to the French and Italian words for damage to a ship's cargo, average derives from the Arabic awar, loss or damage at sea.

Mendel uses both Durchschnitts and mittlere to refer to average values and ratios, and it seems that he is talking about the mean in every case. A tutorial on averages will be available soon in MendelWeb.

1. the upper angle between a leaf or bud, and the stem on which it is born. 2. located on, along, or around an axis. 3. arranged along an axis, in contrast to a terminal position, at the end of the axis. 4. forming an axis.

1. the upper angle where the small stem of a plant joins a larger one, or where the leaf stalk joins the stem. From the Latin axilla, armpit.

1. the main stem, or central part of a plant, about which other parts are arranged. 2. a straight line about which various parts of an object are arranged, rotated, or otherwise oriented. 3. a line which symmetrically divides an object. From the Latin word for axle or pivot.

1. the undeveloped state of a branch or flower,shoot or stem, sometimes protected by leaves. 2. the immature shoot or protuberance from which a stem, leaf or flower develops. 3. a flower or leaf that has not fully opened. 4. an asexual outgrowth from an organism that separates it from an offspring or new individual.

Bruchus pisi
This is most likely a reference to the beetle, Bruchus pisorum, a natural parasite of Pisum. Sometimes called a Pea Weevil this insect uses the pea plant in order to produce its offspring. [These links go to the wonderful entomology site at UIUC.]

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1. the sepals of a flower considered collectively; the outer layer of sepals surrounding the flower. 2. the collection of sepals forming a protective layer around the bud. 3. any cup-like cavity or structure. From the Greek Kalux, the husk or the case of a bud; perhaps from kalupto, to hide.

1. that which is responsible for, or gives rise to, an action, event, phenomenon or condition. 2. a reason or motive; grounds that may be held or cited to justify something. 3. a reason or basis for an effect.

1. the absence of design or discoverable cause. 2. the course of events considered as a self-sufficient power; Fate. 3. the unknown or unpredictable element in events that seems to have no assignable cause. 4. (adj) unexpected, random, fortuitous or accidental. From the Latin cadere, to fall or befall.

Mendel uses "chance" ("Zufall" or "zufällig") in at least two distinct ways: first, to describe the indeterminacy concerning which individual pollen cell will unite with which individual egg cell; and second, to describe the actual fluctuations of his data, relative to a fixed or predicted ratio.

characters, characteristics
1. a set of identifiable and accurately describable traits or qualities which are essential marks of a particular group, species, family, etc. 2. the set of distinguishing features of a class of objects. 3. definable traits that can be transmitted to offspring. 4. any detectable qualities of the phenotype of an organism. 4. whatever distinguishes a plant or group of plants from others. From the Latin character and the Greek kharakter, meaning stamp or impress.

In the first few sections of the paper Mendel uses these terms to refer exclusively to particular aspects of the appearance of the peas and plants. Later, with the introduction of the term "hybrid-character", he sometimes uses "character" to refer both to qualities of appearance and the qualities of internal composition (what we might now call "genetic make-up").

1. to compare or put together in order to identify points of agreement and disagreement. 2. to bring together from different sources. 3. to assemble in a proper sequence. From the Latin collat-, to collect.

Despite the modest introduction, this sentence presents one of the most important conclusions of the paper; it is the generality of Mendel's claim which motivates the discussion of laws of combination in the following section.

combination series
By representing the reproductive contribution of each parent as an algebraic series (i.e. terms linked by "+" signs), we can represent the outcome of any particular cross as the product of those series. This product is called by Mendel the "combination series." But Mendel cleverly argues the converse as well: if we obtain results of a cross that can be modeled as a combination series, then we can determine the reproductive contribution of each parent, and can also know how individual characteristics behaved in the cross.

Mendel first uses the combination series to support the claim that each of the seven characters are inherited independently of one another. That is, he argues that the combination series of a two-character or three-character cross, corresponds to the product of the combination series representing each of the individual character crosses. Later in the paper, Mendel uses this same sort of argument to advance a theory about the composition of the reproductive cells of the hybrids.

To get a better idea of how the combination series is used in Mendel's arguments, consider two plants that are both hybrids with respect to one particular character; let S and s to represent the two forms of the character. Suppose you cross these hybrids, and observe that the experimental results can be represented accurately by the series: S + 2Ss + s; that is, you get S and s offspring in a 3:1 ratio, and (waiting another generation) you find that 2/3 of the S offspring must have been themselves hybrids. Then, you may argue, if the series is accurate then the contribution of each parent is known, and can be represented by the series S + s. That is, you can conclude that each parent must have produced both S and s reproductive cells, in equal proportions.

Mendel's use of combination series offers an excellent example of the use of a mathematical model to carry both experiments and arguments forward.

composition, internal composition
1. the way in which ingredients or parts are combined. 2. the make-up of a mixture. 3. the arrangement and nature of the parts within a unified whole. From the Latin componere, to put together.

Mendel uses this term to refer exclusively to the information contained in the reproductive, or sex, cells; today we might say he is referring to the "genetic make-up" of these cells. Keep in mind that Mendel's speculation about the composition of the reproductive cells is derived from, and supported by: 1) his observations concerning the appearance of the offspring produced by those cells; and 2) his use of the combination series as a model for the forms of those offspring.

1. in agreement with. 2. harmonious, agreeing. From the Latin concors, of one mind.

This is a translation of übereinstimmendes, which Mendel uses frequently; elsewhere the Druery-Bateson version translates this word as "agreement."

1. combined or joined. 2. combined or united while maintaining separate identities.

By translating both vereinigt and verbundenen as conjoined (rather than as "united" or "allied"), Bateson seems to have emphasized the point that the characters combined in the hybrid were joined, but not blended.

constant combinations
Mendel uses this phrase to refer both to the individual terms of the combination series (ignoring their coefficients), and to the combination of different characters within a particular organism. For example, in a single-character cross between two hybrids, Aa, we have seen that the experimental outcome can be represented by the combination series A + 2Aa + a. Here there are three constant combinations: A (the pure dominant), Aa (the hybrid), and a (the recessive).

Mendel repeatedly notes that the constant combinations that are observed in the offspring from a particular multiple-character cross, are exactly those that appear in the combination series generated by multiplying the combination series of each single-character cross. This is meant to strengthen the view that the combination series provides an accurate representation of any cross; and therefore, to support Mendel's conclusions about the composition of the reproductive cells, which themselves depend on the validity of the combination series representations.

1. the make-up or composition of something. 2. a person's physical state, specifically with regard to health. 3. the body of fundamental laws, principles, or precedents, according to which a government, or other institution, is governed or constrained. Derived from the Latin statuere, set up.

Bateson uses this word to occasionally translate Entwicklung, development; as well as Beschaffenheit, which is elsewhere translated as "composition". The effect of the latter, it seems, is to dissolve some of the ambiguity of Mendel's original language, by distinguishing references to the informational content of the reproductive cells, from references to their material organization.

1. to tighten or make narrow. 2. to cause living tissue to contract. 3. to compress or bind in order to make smaller. From the Latin stringere, to draw tight.

The constricted form of the pod is characterized by its appearing to be pinched or indented between the spaces occupied by the peas. This is in contrast to the "inflated" (or more convex, or domed) pod, which does not exhibit constrictions between the peas.

continuous evolution
Gärtner opposed the view that new species of plants and animals arose from the crossing and gradual development of old species; instead, he believed that each species was created separately and could only develop and change within limits inherent in its nature. Furthermore, he thought that artificial hybridization experiments, which appeared to break these boundaries, merely demonstrated how unbreakable were the natural boundaries.

Although Gärtner was certainly opposed to at least elements of an evolutionary theory, Bateson's translation of Fortbildung as "continuous evolution" is not particularly accurate; the German term implies both development and improvement (here it probably should be translated as "progressive development"), and one can certainly oppose a directional notion of development, without being opposed to evolution. When Mendel appears to be referring to a theory of evolution, elsewhere in the paper, he consistently uses the term Entwicklung. Whether the latter ought to be translated as "evolution" or "development", given Mendel's knowledge of Darwin and other evolutionists, is a debatable question.

What is perhaps most interesting about this reference to Gärtner's view, is that it demonstrates how different scientists could interpret the results of hybridization experiments as supporting contrary theories about the origin and development of species. For more on this topic, see Jan Sapp's "The Nine Lives of Gregor Mendel".

1. (n) a standard or source for comparison in checking the results of an experiment. 2. a standard of comparison used to check the conclusions inferred from an experiment or study. 3. an experiment used to verify another experiment, using conditions that are identical except in one or a small number of respects. Related to the Middle English controllen, and the Anglo-French contreroller, to keep a copy of a register or roll of accounts; from the Medieval Latin contrarotulare, to check by a duplicated register.

This is perhaps the earliest use of "control" (Mendel's term is Kontrolle), at least in the biological sciences, to denote an experiment, or set of experiments, run in parallel with others, and differing only in a single respect, or only with respect to environmental factors. In this case, the controls are the plants grown in the greenhouse, while the main experiment is conducted in the open air.

The O.E.D. cites Charles Darwin, in his book Insectivorous Plants (1875), as the first to use the word in this way in English. By 1900, this usage is so well accepted that it appears in Jackson's Glossary of Botanic Terms. But at the time of Mendel's experiments, controls (in the sense used here) were certainly not part of the standard methodology in botany, or in biology generally.

correct experiment
Mendel's idea of a correct, or well-formed, experiment seems to have come largely from his formal studies of experimental physics. In 1851, eight years after entering the Augustinian monastery in Brno, Mendel was sent to the University of Vienna, to study physics at an Institute directed by Professor Christian Doppler -- the same Doppler known to students of modern physics because of the effect that bears his name. In addition to taking more than half his courses in the areas of physics, mathematics, and chemistry, Mendel enrolled in a special seminar, conducted by Doppler, concerned with the proper design and demonstration of experiments in experimental physics. (for more on Mendel's education at the University, see Orel [1984], ch. 3).

Mendel used the term "korrekt" only once in his paper; elsewhere, when Bateson used the word "correct" to translate the German (e.g. "correct assumption"), Mendel had used the term "richtig" ("right") or one of its cognates. For Mendel, a "correct" experiment was one precise enough to clearly answer a narrow, well-formed question. Unlike most of his predecessors and contemporaries, Mendel investigated plant hybrids by performing experiments that focused on the behavior of single traits. Similarly, these experiments were designed to answer elementary questions about how the particular characteristics of individual plants were inherited from one generation to the next.

1.the first leaf or leaves of a plant, often containing nutritive material. They may be located above or below the ground, and, in peas and many other plants, the cotyledons are usually different in form from the leaves produced afterward. 2. any of the thick and fleshy plants in the genus Umbilicus. 3. Former name of the genus Adromischus. The term was apparently introduced in botany by Linnaeus, and derives from the Greek kotuledon, meaning cup-shaped cavity.

cross, crossed, crossing
1. uniting the reproductive cells of one organism with those from an organism of a different kind, in order to produce a hybrid. 2. (in plants) to unite the pollen from the flower of one plant with the eggs from the flower of another plant; the two plants usually differ in some respect(s). 3. (in viruses) to infect cells with particles from different viruses. From the Latin krux.

Mendel usually used the term Befruchtung, or "fertilization", to refer to the process Bateson translated as "crossing". This involved uniting the pollen from one plant with the eggs of another; Mendel was able to do this using a small brush to take some pollen from the anthers of one flower, and then dust or sprinkle the pollen onto the stigma of the flower of the second plant.

Mendel was primarily interested in cases where the two plants being crossed differed in one or more characteristics; but, at the start of the paper, he was anxious to show both that this process of artificial fertilization did not affect the fertility of the plants, and that his results were not dependent on which parent he chose to provide the pollen and which the eggs.

1. to grow or promote the growth of plants, crops, or other biological organisms. 2. to prepare or use for growing (e.g. cultivating the soil). 3. to attend to or promote the friendship of another. From Medieval Latin, in which the phrase cultiva terra means arable land.

Mendel emphasizes the care required to perform his experiments in a number of places in the paper. Here, rather than use the term "grown", he uses "cultivated" (angebaut), which calls attention to the important and active role of the experimenter.

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1. to conclude or derive on strictly logical grounds. 2. to reach by reasoning rather than observation. 3. to infer or draw as a logical conclusion. Derived from the Latin ducere, to lead.

Bateson used the term "deduced" to translate of variety of German terms, none of which were the logical term deduzieren. Mendel's choices of terms (e.g. ermitteln [to ascertain or determine], erwiesen [to prove, or show]), clearly emphasize the role of observation and empirical investigation (in addition to logic) in reaching true conclusions.

1. to mark, indicate, or signify. 2. to be the sign or symbol of something; e.g. flashing red lights may denote the presence of railroad tracks. 3. to mean (literally), or refer directly, as opposed to "connote": to imply or suggest, in addition to the direct, or literal meaning; e.g. the term "rose" denotes a certain kind of flower, but it has romantic connotations in some cultures. From the Latin notare, to mark.

This is a translation of Mendel's term "bezeichnen".

1. harmful, causing damage. From the Latin deterere, to rub off or wear away.

This is one of several places in the paper in which Mendel discusses the details of, and potential difficulties involved with, carrying out (and perhaps repeating) the experiments he describes. He uses the term "gefährlich", which might be better translated as "dangerous".

1. not possessing. 2. completely empty or lacking; vacant. From the Old French devoidier, to empty.

Here, Mendel argues that the inheritance of flower color may in fact follow laws, and that such laws may be discovered by the sorts of experiments he is carrying out. He characterizes the opposite view as a willingness to think that flower color in cultivated plants is "random and accidental" (regellose und zufällige).

Dianthus drawing Dianthus
A large genus of ornamental plants that includes carnations, and Sweet Williams, among many other species. It is native to the Mediterranean, and parts of Asia, but is widely cultivated.

differentiating characters/characteristics
Mendel here refers to the particular aspects of appearance which distinguish one set of experimental peas and plants from another. For example, pod shape is a differentiating characteristic, because every pod is either inflated or pinched, and no pod is both inflated and pinched; thus the set of all pods may be differentiated according to this characteristic. Mendel uses the phrase "differirende merkmale"

1. different, or varying one from another. 2. composed of different properties or qualities. 3. assuming different forms, or capable of assuming different forms.

Mendel uses this term to denote plants, and later characteristics of plants, that have no apparent, or obvious, connection with one another. Thus he writes first of the need to do experiments with plants from diverse orders, and then of testing the "law of development," derived from observing single traits, by examining diverse characters. In the latter case, he means traits like plant height and pea color, that are "diverse" inasmuch as they are different, apparently independent characteristics of the plants.

1. exercising the most power or control. 2. the most prominent, or prevailing. 3. (in classical genetics) the one of the pair of opposite Mendelian characters that appears, or is observed, when both are present in a single organism. 4. (in modern genetics) the allele, or the effect produced by the allele, that results in the same phenotypic effect whether inherited with a homozygous or heterozygous allele. From the Latin word dominari, to dominate.

Mendel uses this term (dominirend) to describe the forms of the characters that appear in the hybrid generation, in which the two parental forms of each character are crossed. The form of the character that does not appear in the hybrids, he calls the recessive.

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1. The reproductive cell, or ovum, produced by female birds, and by many species of fishes and reptiles. 2. The round or oval reproductive body usually composed of an embryo and nutritive material, often with a protective covering. 3. (egg cell) the ovum or "female" reproductive cell or gamete. From the Middle English term, egge, for a bird's egg.

When Mendel uses the phrase "hybrid egg cells", he is referring to the egg cells produced by the hybrid plant. The egg cells themselves cannot be hybrid because, according to the theory advanced in the last half of the paper, each egg carries only one form of each trait. In modern terminology we would say that each egg cell carries only one allele at each genetic locus.

1.(adj.) Requiring extremely careful attention to a number of details. 2. (adj.) intricate or complicated as the product of careful effort. 3. (verb) to explain or state something in greater detail. From the Latin laborare, to work.

1. (verb) to work or set out with a specific purpose. 2. to make a serious effort or attempt. 3. (noun) a purposeful effort, activity or attempt; an activity undertaken with purpose and sincerity. From the Old French word (devoir) for "duty".

It is perhaps significant that Bateson uses "endeavor", rather than the plainer word "try", to translate "Versuchen" in this case. Elsewhere, of course, the word "Versuch" is translated as "experiment" by Bateson, rather than as "trial".

1. in many seeds, the nutritive tissue surrounding or adjoining the embryo; sometimes called the "perisperm". 2. the albumen of a seed in Angiosperms, sometimes limited to the nutritive material deposited inside the embryo sac.

Though Mendel uses this term interchangeably with albumen, it should be noted that peas possess neither an endosperm nor an albumen; in the plants with which Mendel was working, the cotyledon carries out these nutritive functions.

1. puzzling or mysterious. 2. difficult to grasp or figure out in the way a puzzle is difficult. From the Greek ainigma, riddle.

1. a condition in which opposing forces are equal or balanced. 2. balance 3. (chemistry) the state in which the products of a forward or direct reaction are consumed by a reverse, or second, reaction at the same rate at which they are formed. From the Latin libra, meaning balance.

In this section Mendel discusses the experiments of Gärtner and Kölreuter concerning the transformation of species. Although 19th century botanists had a rather different view of species than did their contemporaries studying evolution (e.g. in geology and natural history), this section implies Mendel's familiarity with evolutionary theories concerning the origin and transmutability of species. As has been pointed out by Hartl and Orel [1992], and others, Mendel read the German translation of Charles Darwin's Origin of Species, published in 1863; a copy of this book was found in the library of the monastery in Brno, and contained Mendel's notes and commentary in the margins.

The connection between Mendel's views on continuous evolution and his interpretation of his experiments is not obvious. Little is known about whether he thought his findings compatible with the theories advanced by Darwin, and such questions have not always seemed important to modern biologists studying Mendel; when the Bateson translation was published in Peters [1959], a widely read sourcebook in genetics, the concluding section of Mendel's paper was omitted.

1. mistaken, or deviating from the truth. 2. based on, or containing errors. 3. (obs) roving; irregular; unsettled. From the Latin errare, to wander. Mendel's original term (irrigen), comes from the same Latin root.

1. (adj.) basic and of fundamental importance. 2. being an inherent or intrinsic part; being part of the essence of something. 3. (noun) a necessary or fundamental part or aspect; e.g. "When he goes hiking, or when he goes to the library, my friend considers chocolate an essential." Ultimately derived from the Latin verb (esse) "to be".

One of the great difficulties in performing the botanical experiments described by Mendel, is that each time the experiment is performed, the experimental conditions have changed in numerous ways. Time has passed, the weather is always different, the presence of insects or harmful parasites may change from one season to the next, and, unlike the atoms and particles of physics, no two biological organisms are strictly identical. Mendel therefore had to distinguish between the differences in experimental conditions and results he considered important, and those he did not; a task that was often difficult.

Mendel uses this term ("wesentlich") several times in his paper, most often to distinguish between experimental conditions and results he considered significant, from those he thought accidental or due to chance. That such a distinction always involved interpretation is best seen in his use of the term in final section of the paper.

1. Easily perceived or understood; obvious. 2. Clear or apparent. 3.Plain or easy to see; visible. Like evidence, evident is derived from the Latin evidens, clear or visible, which in turn comes from the verb videre, to see.

The first time "evident" is used in the English version, it turns the German double-negative Ein gründlicher Beweiss, which might better have been translated "A thorough demonstration."

Skeat notes that "evident" in used in Chuacer's Treatise on the Astrolabe (1391), perhaps the earliest example of scientific writing in English. Indeed, the term has played an enormous, and perhaps under-appreciated, role in the development (and promotion) of English and American science.

In 1927, after Mendel's work became widely known but before Mendelian genetics and Darwinian evolution were thought obviously compatible, Richard Swann Lull wrote:

We can contrast this general definition with the specific theory of evolution advanced by Charles Darwin, in Origin of Species; it was Darwin's view that the organisms we see today have all descended from common ancestors through a process of "descent with modification"; and that the most important mechanism of evolution, the primary cause of these modifications through time, has been natural selection.

Although the phrase "history of the evolution" may be a reasonable translation of Mendel's Entwicklungs-Geschichte, and Entwicklungsgeschichte it would be wrong to conclude that Mendel was talking about any particular theory of evolution. Although we know that Mendel was interested in , and read Origin of Species before 1865, we have no evidence that he thought the specifics of Darwin's theory particularly relevent to his experiments with peas. Indeed, Mendel often seems to have used Entwicklungsgeschichte, in contrast to Entwicklung, simply to distinguish the historical development of species from the development of the individual organism.

1. to show or display or present to view. 2. to show or present outwardly. 3. to present for public viewing or consumption. 4. (Law) Something, such as an object or a document, presented as evidence in court. From the Latin exhibere, to hold forth or present.

The use of the term "exhibit", like that of evident, introduces a sense of direct perception, or at least direct visual experience, that is perhaps missing from Mendel's original. For example, the Bateson translation uses "exhibit" to translate the German erhalten, which might better have been translated as "receive" (or even "maintain") in this context.

1. A test conducted to establish the truth or falsity of a hypothesis. 2. One or several trials performed in order to demonstrate, discover, or investigate, what will happen under specific conditions. 3. a procedure carried out over time in order to try or test hypotheses; an attempt to demonstrate, discover, or search by means of experiencing the outcomes of such a procedure. From the Latin periri, to try (a root for both "experience" and "peril").

Although the earliest uses of the English term "experiment" come from alchemy, by the end of the 17th century an "experimental method" was considered to be an essential, and perhaps unique, quality of scientific investigations. Versed in the methods of chemistry and physics, and having recieved training as an experimental physicist at the University of Vienna, Mendel insisted not only on the importance of experiments in the study of plant hybrids, but on carefully designed experiments, by which he seems to have meant experiments modeled on those of physics. In the Introduction to his paper, Mendel mentions the need for detailed experiments (Detail-Versuche), that could discover the patterns of inheritance for particular characteristics; he also has an idea of what constitutes correct experiment, which is mentioned later in the paper.

In the original, Mendel used both "Versuche" and "Experimenten" to refer to experiments. Sometimes he used "Versuche" to refer to individual trials or experiments, while using "Experimenten" for discussions of experimentation per se, or references to the collection of individual experiments; but the logic behind his usage is not obvious.

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1. to make easier. 2. to reduce the effort necessary in making something possible. From the Latin facilis, easy to do.

1. a category in the biological classification of plants and animals coming below an Order and above a Genus. 2. A subdivision in the classification of plants, with names usually ending with -aceae or -osae (e.g. Leguminosae). 3. A category of social grouping usually consisting of two or more adults and their offspring, frequently living in the same place. From the Latin familia, meaning household or the servants in a household; from famulus, servant.

Although Mendel did use the term genus in its correct taxonomic sense, it is not clear that he was using "family" in such a precise way. In modern taxonomy, we recognize five kingdoms of organisms, and use the categories: Kingdom, Phylum (called Division in plants), Class, Order, Family, Genus and Species, to classify plants and animals. In Mendel's time, however, classification was based on a more limited system, proposed by the botanist and natural historian Carl Linnaeus (1707-1778), and each species of organism was designated by two Latin names, the first denoting the genus and the second the species (e.g. Pisum sativum).

1. capable of carrying out or supporting reproduction. 2. able to conceive offspring or produce fruit. 3. (in Botany) having a working set of reproductive organs. 4. (of soil) capable of producing abundant crops. From the Latin ferre, to bear.

In his investigations, one of Mendel's concerns was how hybridization affected the fertility of plants, and whether or not these effects were relevant to the formulation of laws of inheritance. Today we believe that when members of different species are crossed, their offspring, if they develop at all, will be infertile; but, it can also be the case that hybrids have reduced (or in rare cases enhanced) fertility.

In the Bateson translation, "fertility" and "fertile" are usually translations of the more illustrative terms "Fruchtbarkeit" and fruchtbar.

1. secured or made stable. 2. Constant, not subject to variation or alteration. 3. rigid or fastened. From the Latin fixus, which is the past participle of figere, meaning to fix or fasten.

The word "fixed" appears twice in the Bateson translation: first, in reference to the 2:1 ratio observed between the offspring of the F1 dominants that produced both dominant and recessive F2 characteristics and those that produced only dominant F2 characteristics; and second, in reference to the belief that there are definite limits to how species may be transformed through cross-breeding. An interesting analogy is thus drawn, in the English version, between the discovery of genetic ratios and the discovery of species boundaries. Mendel did not use the same word to describe the two situation in the original, however, using gesichert in the case of ratios, and fest in the case of species limits.

1. continual irregular variations in degree or number. 2. movements up and down, or back and forth. 3. continuous changes that are irregular, at least for short periods of time. From the Latin fluctus, a flowing (as of a water wave).

Mendel uses this term most often when discussing ratios, which seem clearest when the number of experimental plants (or seeds) is large. This is only to be expected, because when the number of plants is small, a small number of chance variations have more weight in the computation of averages.

English and American scientists reading the English word "fluctuation", around the turn of the century, would necessarily have thought of statistics and perhaps statistical physics; by 1901, the literature of physics had established a successful way of talking about laws and systematic relations that could be seen despite, or underneath random fluctuations (e.g. particles in a magnetic field). That the Bateson translation used "fluctuation" to translate a word like Störungen (rather than "disturbance" or "interference"), may be more indicative of what the translator considered good scientific thinking, than of Mendel's own thoughts.

1. the ordinary green leaves of a plant or tree, as opposed to those that are transformed into petals, bracts, scales, etc. From the French word for leaf, feuille.

1. Surgical pincers used for extracting or grasping. 2. A tool usually consisting of two pieces connected at one end, that can be brought or pinched together to hold or manipulate an object. 3. The name given for pincher-like appendages in some insects. The Latin word forceps is thought to come from combining formushot, with capere to seize (i.e. something used to seize hot things).

Mendel used a term originally borrowed from French, Pincette.

foundation and explanation
Mendel emphasized this phrase ( Begründung und Erklärung), to stress that the ratios he had found, and the combination series he had used to model those ratios, made sense and were predictable given the assumption that the hybrids produced pollen and eggs carrying both dominant and recessive characteristics, in equal proportion. One might argue that it was especially important for Mendel make this strong claim at this point in the paper, because the following section reports the comparatively inconclusive results from experiments with other species of plants.

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1. The group of organisms produced at approximately the same time; a group of organisms at the same stage in the life cycle. 2. The average period of time from the birth of an organism to production of its offspring. 3. The group of people, generally within a single society, born at approximately the same time. 4. A class of objects derived from, but significantly different from, the previous class. From the Latin generare, to produce or beget, which derives from genus.

When Mendel writes of successive generations of peas, he means the successive years' offspring from the parental (true-breeding) strains. Thus the first generation from the hybrids (F1), are the offspring of the hybrids, which are themselves the offspring of the parental strains; thus the F1 is actually the second generation from the parental strains.

The generation time for Mendel's peas is approximately one year; that's the time it takes from the appearance of a single pea (in late summer or early Fall) to the appearance of that pea's offspring (the following season).

1. a grouping of one or several species that possess common characteristics. 2. a category of biological classification above species and below family. 3. a class of objects with common characteristics or attributes. From the Latin genus, meaning kind, or race.

In biological terminology the name of the genus and species to which an organism belongs is sometimes called its "generic" and "specific" name, respectively. Thus Pisum is the generic name of the plants Mendel was using.

1. to sprout, or develop. 2. to bud or produce shoots. 3. to come or develop into existence. From the Latin germinare, to sprout.

Geum drawing Geum
Plants belonging to the genus geum, in the Rosaceae family, bearing flowers with four or five petals. (e.g. Geum rivale, and Geum triflorum [sometimes called "Prairie Smoke").

1. A building, often composed primarily of glass, designed for the cultivation of plants. 2. a building mainly of glass, for the growing and protection of delicate plant, or for controlling their growth.

Mendel's use of the greenhouse in these experiments was extremely important, because it allowed him to run controls, which in turn allowed him to make stronger analyses of both the results his theory predicted, and those that seemed exceptional (e.g. his attributing false impregnation in the garden to the presence of the beetle, "Brucus pisi").

(Although Andrew Faneuil of Boston is said to have built a glass house before 1737, the first greenhouse in the United States is generally attributed to James Beekman, who built one in New York City in 1764.)

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1. The offspring of two species of the same genus, or two varieties of the same species. 2. A plant obtained by the pollen of one species uniting with the stigma or egg of another. 3. something composed of elements of different kinds or types. From the Latin Hybrida ("mongrel"), the English term was first used in its biological sense around 1600.

Although the term hybrid now enjoys a fairly precise definition, in Mendel's time both hybrid and hybridization were often used to describe cross-fertilization between any species or varieties that were thought by breeders to be significantly different. The term "mule" was then used to denote sterile hybrids. Today, we believe that the offspring of two different species, if they come to be born at all, will be sterile; thus, we would say that what Mendel calls a "hybrid" is really the offspring or progeny of distinct varieties rather than species.

1. The fertilization of the flower of one species by the pollen of another species. 2. The art of obtaining hybrids by artificial crossing. 3. The production of hybrids that occurs in nature.

1. A statement used as a basis or starting point for investigation or reasoning. 2. A explanation tentatively accepted for the purposes of experimentation or argument, where the experiments and arguments are meant to help determine whether or not the explanation is true or valid. 3. An assumption, usually made in order to continue an analysis. From the Greek hupotithenai, to suppose.

Mendel often stressed the tentative nature of his conclusions, based a they were on a single set of experiments on particular species of plant. But he also stressed the need to continue investigations, not only on Pisum but on other flowering plants as well.

Mendel used the term Hypothese only once in his paper. He used the less formal term Annahme (assumption) many times, and the Bateson version used the terms assumption, theory, and hypothesis to translate it.

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impress their peculiarity upon
One of the most fascinating aspects of Mendel's paper is his success in describing the patterns of inheritance, without having any knowledge about the biological mechanisms responsible for those patterns. Although it was well-known by 1865 that peas, like all plants and animals, were made up of cells, Mendel had no knowledge of what the genetic material of the cell could be. More importantly, perhaps, he didn't have the language of genetics to reason about such things.

Mendel's use of mathematics (the combination series in particular) is important in this respect, because mathematics made it easy to avoid questions of biological mechanism. When he was forced to go beyond mathematics and to use natural language to describe what he saw, his description problems became more difficult. A nice example of the difficulty is seen in his use of the strange phrase "must impress their peculiarity upon" (Eigentümlichkeit aufprägen müssen), to describe dominance.

1. Not depending on, linked to, or affiliated with an other (e.g. another object, factor or group). 2. Not determined or governed by another or others. 3. (in mathematics) a variable which, when its value is changed, causes a change in another variable; yet, not itself dependent on other variables.

According to the OED, the English word independent first appears around 1610, and comes directly from the French indépendant and/or Italian independente. Ultimately, the term derives from the Latin pendere, to hang; a root shared by Mendel's term unabhängig, which he used to refer to the independence of characters.

The phrase independent assortment is often used to describe one of Mendel's laws or discoveries, based on the experiments described in this paper. The phrase means that the patterns of inheritance of individual traits, or characters are independent of other studied traits. For example, Mendel finds that the inheritance patterns and ratios for pea color are uninfluenced by pea shape, pod shape, or the length of the plant stem.

Today, we believe that this independence has to do with whether or not the gene or genes that code for different traits are on the same or different pairs of chromosomes. Mendel knew nothing of chromosomes, of course (their significance for the study of inheritance was not known during Mendel's lifetime), so it is remarkable that he reported his investigations of exactly seven traits in Pisum, finding each independent of the other, and that Pisum in fact has seven pairs of chromosomes. Given Mendel's expertise as a gardener, and his ad hoc selection of seven characters to study (he describes more than a dozen) it is reasonable to assume that he knew that seven independent characters was the limit in peas.

Mendel used the term unabhängig to describe the independence of traits, and Selbständigkeit to describe the independence of species.

1. A disposition or tendency to behave one way rather than another. 2. A preference for, or leaning toward, one set of thoughts or actions rather than another. From the Middle English enclinen, ultimately from Latin clinare, to lean.

Here, Mendel reports confirmation of the observations of Gärtner and Kölreuter, each of whom had noted that, over time, the number of parental forms increases at a faster rate than the number of hybrids. Mendel refined their views by describing how this generation of parental and hybrid forms worked for individual traits. That is, he noted that while parental forms, both dominant and recessive, breed true generation after generation, hybrids produce parental and hybrid forms as offspring; therefore, the ratio of parental forms to hybrids increases over time. This increase is dramatically illustrated table in the seventh section of the paper.

Throughout the paper, Mendel reports and speculates about the laws governing the inheritance of traits (what we now call the science of genetics), but he does so without knowing the mechanism responsible for these laws. His use of the term "inclined" (Neigung), is a nice example of the difficulty he had in relating his deterministic findings without a mechanistic language.

"internal nature"
inter se

Taken from the name for the piece extending the length of the bottom of a boat, usually forming a ridge, the keel is often a prow-shaped structure formed by the petals at the top of the flower. In Pisum, this petal structure completely covers the sepals and the reproductive organs of the flower.


Lathyrus drawing Lathyrus
A genus, of the pea family (Leguminosae), sometimes called the sweet pea or wild pea, although those are but two of the 150 species known today. Lathyrus are annual and perennial herbs, often distinguished by their clusters of irregular flowers, each with five petals. This name comes from the Greek thoures, stimulant.

Lavatera Arborea
drawing Lavatera
A genus of the Mallow family, comprised of more than 20 species of herbs and subshrubs. Species of Lavatera are usually distinguished by flowers with five notched petals, and fused stamens.

"law of probability"
leaf, leaves

The pea and bean family, and the third largest family of flowering plants, with more than 16,000 species known today (Allaby, p. 227). One reason for their numbers is that the roots of Leguminosae usually hold nodules containing nitrogen-fixing bacteria. Because the plants can convert atmospheric nitrogen into useful nitrogenous compounds, they are able to grown under a wide range of soil conditions.

The "peculiarities" (Mendel uses eigenthümlichen) which were most important to Mendel's study were the bisexual nature of the flower, the ovary positioned at the bottom of the flower, and, most of all, the united sepals (which kept out foreign pollen during reproduction).

luxuriance, luxuriant
"mathematical exactness"

mean, median and mode
Three techniques or methods for determining an average. Consider the sequence of numbers and the question: "What is the average of these numbers?":

The type of average you decide to calculate should depend on the sorts of data you are dealing with and the things you want to know about that data. Similarly, when you are presented with an average, it is worth noting which technique was used to calculate it, since taking the mean, median and mode of large data sets rarely yields the same number. See the homework sets for some questions concerning these methods for calculating averages (e.g. Problem 5 of set #1 )

When Mendel referred to averages, he was always referring to the mean. The English words "mean" and "median" both come from the Latin medius. "Mode" was not used in this way in English until 1895.

"ornamental plants"

Phaseolus drawing Phaseolus
Known most commonly as bean plants, Phaseolus is a genus of the family Leguminosae. Mendel discusses several species of this genus, including Phaseolus vulgaris.

1.the observable characteristics of an organism, produced by the genetic material in conjunction with the environment. 2. the appearance of physical and biochemical parts of an organism, as distinct from the composition of its genetic material (or genotype.

"Phenotype" was first used in 1909, by the geneticist Wilhelm Johannsen (1857-1927), who coined the terms gene and genotype as well. But Johannsen used the term to refer not just to the appearance of an organism, but to the average appearance of self-fertilizing, apparently "constant" forms. The current sense of the term was developed later, but was well-established in genetics by the mid-1920s (e.g. Sinnott and Dunn [1925], whose genetics textbook was dedicated to "the work of Gregor Mendel"). For more on the history of the terms phenotype and genotype, see Churchill [1974].

Mendel drew the distinction between the forms of characters that appeared in a particular generation (i.e. dominant and recessive) and the "internal nature" of the plants that exhibited those characters (parental and hybrid). This distinction is the basis for the contemporary distinction between the appearance of an organism (its parts as well as its molecules) and the genetic material that, along with the environment in which the organism develops, determines that appearance.


Pisum sativum drawing Pisum
A small genus of the family Leguminosae. Species of Pisum are distinguished by their five united sepals and five fused petals. "The upper petal .. is held erect, the 2 lateral petals or wings are usually spread, and the lower 2 petals are held together to form the keel." (Hyam and Pankhurst, p.396)

Mendel performed most of his experiments on the garden pea, Pisum sativum

The grains produced by the anthers that carry reproductive or sex cells (gametes). In Pisum the pollen are considered the "male" reproductive cells, while the eggs are considered the "female" cells; of course in such plants this distinction is primarily metaphorical. The English and German words both derive from the Latin term for mill dust and finely ground flour, pollen. (According to Barnhart [1988], p. 814, the Latin may be cognate with the Sanskrit palala-m, meaning ground seeds or porridge.)

Mendel used the phrase "foreign pollen" to describe pollen of unknown origin that might accidentally fertilize one of the flowers on which he was experimenting. The closed keel of the pea flower made this significantly less likely than it would have been in other species of flowering plants.

"practical proof"
"reciprocal crossings"
"reproductive cells"

The separate sections or leaves of the calyx, this term comes from the combination of the first syllable of the Latin separare with the Latin word for petals, petalum. Thus "separate petals" is a fair description of the sepals.

"serial arrangement"

1. the new growth of a plant or flower. 2. the ascending axis of a plant, which later becomes the stem. 3. the young sprout, branch or twig of a plant. From the Middle English shoten, to dart or spring forward.

significance, signification

1. a group of animals or plants with very similar characteristics and evolutionary histories, capable of producing fertile offspring by interbreeding. 2. a category of biological classification, below genus, referring to a group of organisms with similar physical and behavioral traits and capable of producing fertile offspring by interbreeding with one another. 3. a group of organisms that share an environment and have such similar genetic characteristics that they can interbreed and produce fertile offspring. 4. a kind or type. Though the term comes from the Latin species, meaning "kind" or "form", the use of the term for biological classification is due to Linnaeus (1707-1778).

The meaning of "species" in biology has been the subject of much study and debate since the middle of the 19th century, and the meaning of the term has changed since Mendel's time. Consider the following explanations of "species", the first from a standard early 19th century botany textbook (by the naturalist Asa Gray), and the second from a recent textbook on evolutionary biology (by Douglas J. Futuyama):

Mendel was aware that writing about species raised problems of definition and though he certainly considered the term useful, he seems to have felt that the issue of precisely distinguishing between species and varieties was not crucial to his experimental results or his theorizing about the laws governing hybrids. This is especially clear in the original (German) text, where Mendel rarely uses the formal term Species; instead he uses the less-committed term Art (or words composed from it) most often. While Arten was certainly a word for biological species, in botany it was also used as a term for varieties. As these different words were (usually) translated as "species" in the Druery-Bateson version (and in the Stern-Sherwood translation as well), it is understandable that, in English, Mendel seems to use "species" inconsistently and ambiguously.

Issues of translation aside, today we would say that in cases where Mendel talks about different species of plants being crossed and producing fertile hybrids, he was in fact a talking about different varieties of these plants.


The reproductive organs of the flower holding the pollen, the stamen includes includes the anthers. From the Latin stamen, thread.

To artificially fertilize a particular flower, Mendel would try to remove all the stamens, and then dust the stigma with pollen gathered from the anthers of another flower.

sterile, sterility
stigma, stigmatic tip
"sufficient explanation"
theory, theoretically
"transitional forms"
true value/ratio

Variance is a statistic that shows the dispersion of a data set, or how varied, or spread out the data is. Knowing that the variance of a sample is low, for example, tells you that the data is closely clustered around the mean. Although there are many ways to measure dispersion, in statistics the variance of a data sample usually signifies the sum of the squares of the differences between each data point and the mean, divided by the number of data points. Another way to describe the variance is as the average squared deviation from the mean. The formula for computing the variance can be written as:

variance = SUM((datapoint-mean)^2))/numberofdatapoints)

For example, suppose you have a set of data points with the following values:

10 10 25 25 35 65 65 85 90 90

The mean is obviously 50, and the variance can be calculated as:

[(10-50)^2 + (10-50)^2 + 
(25-50)^2 + (25-50)^2 + (35-50)^2 + (65-50)^2 + (65-50)^2 + (85-50)^2 +
(90-50)^2 + (90-50)^2]/10 = 955

Sometimes statistics calculated on a sample of data, drawn from a larger population, are used as estimators of the statistics of tha population; that is, the sample statistics are used to estimate the (unknown) population statistics. When this is the goal, the formula given above is often modified so that n-1, rather than n, is in the denominator. We then have:

variance = SUM((datapoint-mean)^2))/(numberofdatapoints-1))

On the Statistics Calculation Page the latter formula is referred to as sample variance and the first formula is referred to simply as the variance. You may recognize that, as the size of the data sample gets larger (i.e. for very large n ), the difference between the two forms of variance becomes small. (For more information about statistics and statistics terms, take a look at the Statistics sites on the Reference Page.)

Finally, the variance is usually calculated so that the standard deviation can be calculated. The standard deviation, which is the square-root of the variance, is also a measure of dispersion; but it used more often than variance to indicate the distribution of the data relative to the mean (see, for example, the discussion of the Normal Distribution and Standard Scores, part of a Basic Statistics course at Arizona State University).

1. a kind or group that possesses certain chracteristics that distinguish it from another. 2. a biological classification for an intraspecific group or population, usually isolated geographically, distinguished by certain characteristics exhibited by each member. 3. a group of organisms that are members of the same species, and have certain characteristics in common that are not shared by all members of the species; sometimes called a subspecies, when the variance within the variety is great and sometimes called a strain (particularly in genetics), which the variance is minimal. From the Latin varius, various.

Although Mendel sometimes uses "species" where we would today use "variety" or "strain", he clearly understands that a distinction between varieties is not the same as a distinction between species. He also seems to understand that two varieties are capable of producing fertile offspring when crossed. But he emphasizes, early in the paper, that the decision to classify two organisms as members of different species rather than different varieties may at times appear arbitrary .

Mendel uses the term Varietäten to refer explicitly to biological varieties, but sometimes his use of the term arten seems to also signify a variety (rather than a species).

"vivifying union"
weak, weakly

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