AMER. ZOOL., 26:749-752 (1986)
Experiments in a Monastery Garden1-2
GREGOR MENDEL
Augustinian Monastery of St. Thomas, Briinn
SYNOPSIS. After a brief account of my early education, study at the University of Wien,
and preliminary experiments on hybridization conducted at the Augustinian Monastery
in Briinn, Austria, I state the reasons for selecting certain features of the edible pea, Pisum
sativum, for extensive investigation of their inheritance. After eight years I reported my
results to the Briinn Society for the Study of Natural Science, and they were published
in the following year (1866) in the Proceedings of the Society. I discovered two basic
principles of inheritance: the law of segregation and the law of independent assortment
of hypothetical units of heredity that I called Elemente. I conclude with some remarks on
the possible relation of my work to the evolution of organic form and on my disappointment
that my studies do not seem to be known or understood, and that because of my administrative duties at the monastery, now being the Abbot, I have no time for further investigations.
meters away. With great sacrifice to them
I went, but it was hard to keep body and
this evening, as announced by your Vor- soul together. Part of the time I was on
sitzer, is on the inheritance of hybrids in half-rations. Eventually, it appeared that I
the common edible pea, genus Pisum. My must discontinue my studies and begin to
interest in heredity began already as a boy earn my own livelihood. But one of my
on my father's farm in Heinzendorf in high school teachers recommended me to
Moravia, a province of Austria. My father the Augustinian Monastery of St. Thomas
had horses and cows, chickens and bees, in Briinn. I was accepted and became a
peas and beans, and flowers—always flow- novice. Later I took my vows in accordance
ers. Being a curious and uninhibited boy I with the rule of St. Augustine. After a few
observed breeding in animals and seed for- years my order sent me to the University
mation in plants. I found breeding of ani- of Wien with hopes that I would pass the
mals more interesting. I often wondered examinations and become an accredited
why the offspring resembled their parents teacher. Well, I did not pass my examinabut were usually not exactly like their par- tions, and so I returned to Briinn and
ents. We had a good teacher in the Hein- became an unaccredited teacher—a good
zendorf school that had opened its doors one, I am happy to say.
only thirty years earlier. Previously the boys
My interest in plants and animals, begun
and girls of Heinzendorf never learned to on my father's farm, as I have explained,
read or write. Their parents were too poor continued during my school years and at
to send them away to school. From my the University of Wien, and became my
teacher I learned much, including growing primary preoccupation at the monastery
fruits and keeping bees.
when I was not engaged in teaching and
When I completed the school my teacher religious duties. I always kept bees and
told my parents that they should send me mice. But I did not like snakes. Yet my boys
to the high school in a town many kilo- brought them to me because they knew
that I did not like snakes. My animal breeding in the monastery, however, was
regarded
as immoral by my superiors
1
From the Symposium on Science as a Way of Knowbecause
it
appeared
that I was playing with
ing—Genetics presented at the Annual Meeting of the
American Society of Zoologists, 27—30 December sex. I had to be particularly careful not to
incur further disfavor of the bishop, a con1985, at Baltimore, Maryland.
8
From Great Scientists Speak Again by Richard M.
servative cleric and a very corpulent man.
Eakin, copyright © 1975 The Regents of the Uni- You see, I had made the mistake of reversity of California, by permission of the University
marking to some friends that the bishop
of California Press.
Danke schon, Herr Professor Moore. Griiss
Gott, meine Damen und Herren. My lecture
749
750
"GREGOR MENDEL"
carried more fat than understanding.
Someone reported me, and after that the
bishop and I were not good friends. Incidentally, little did I know at that time that
I too would acquire stout proportions.
[Mendel pats his stomach.] So I turned from
animal breeding to plant breeding. You see,
the bishop did not understand that plants
also have sex. Gelt}
I had long grown ornamentals for their
lovely flowers, and I had learned to crosspollinate them to obtain interesting
hybrids. But these plants were not suitable
for the study of inheritance. After trying
several kinds of plants I found that the
common garden pea was most satisfactory,
for several reasons. First, seeds of several
varieties could be obtained from seedmen
in the town. Second, the plant grew well
in the little plot assigned to me in the monastery garden. Third, its flower is ideally
constructed for experiments in hybridization. Normally the plant reproduces by selfpollination. But this can be prevented by
removing the stamens, the male organs,
before the pollen is ripe. The flower is like
this. [Mendel uses his hands to illustrate.]
Simply spread apart the petals to reveal the
sex organs inside. Pull out the stamens with
a pair of tweezers, leaving the pistil, the
female organ. Cross-fertilization can then
be accomplished by dusting pollen from a
ripe flower on the pistil by means of a small
brush. The petals enclose the pistil so well
that fine airborne pollen cannot enter.
Thus the chances of contamination are
slight, but I never relied on it. There is the
pesky pea weevil that can enter the bedroom chamber. So I always tied paper bags
over the flowers in my experiments. And
four, there are other advantages to peas.
They are nutritious. I usually carry a pocketful of them to satisfy my yearning. [Mendel produces handful of peas from his clerical gown and pops some into his mouth.]
And when my boys pay no attention to my
lectures or they fall asleep, I simply ask the
Almighty to send down a shower of peas.
[Mendel peppers his audience with peas.]
That wakes them up! Gelt}
in earnest in 1856 and finished them eight
years later, after studying over 10,000 pea
plants. I presented my results in 1865 to
the Briinn Society for the Study of Natural
Science, and they appeared in the Proceedings of our society in the following year.
I found that some features had clear contrasting traits such as tall and short vine or
either red or white colored flowers. In all
I selected for study seven features with clear
and distinct traits. The seven that I chose
were color of seed, shape of seed, color of
pod, form of pod, color of flowers, position
of flowers on the stem, and length of stem.
For each of these features one of the traits
was dominating and the other was recessive. For example, red flower was dominating over white flower; and tall vine was
dominating and short vine recessive. I illustrate what I mean by dominating and recessive.
I have here some red and white sweet
pea blossoms. Let us assume that they are
flowers of the garden peas. Now I cross a
red-flowering plant with a white-flowering
one. [Mendel playfully rubs together red
and white plastic blossoms and looks up at
his audience with a grin.] It makes no difference in the results whether I dust the
pistil of the red flower with pollen from a
white one, or vice versa. All of the next
generation plants have red flowers, one
hundred percent—not a single white
flower. Now, is the white trait lost? No!
When I cross two of the first generation
plants, lo and behold white flowers will
appear in all their purity. The whiteness
was only suppressed by the redness, and
that is why I call white recessive and red
dominating.
Of course, there were red-flowered
plants in the second generation offspring.
When I counted them there were about
three of the reds for every one of the whites.
The ratio is about 3 to 1. Now I say
"about"—it was never exactly 3 to 1. As
examples, I quote from my paper. In one
experiment I had 929 plants: 705 had red
flowers, 224 white ones. The calculated
ratio was 3.15 to 1. In another instance,
After a few years of preliminary studies the ratio was 2.95 to 1.1 think that if I had
to test the purity of my seeds and to select produced more plants my ratios would
features for study I began my experiments probably be closer to the theoretical 3 to 1.
EXPERIMENTS IN A MONASTERY GARDEN
I now proceed to analyze the secondgeneration plants. We discover, not unexpectedly, that the white plants when crossed
with white give white flowers. Actually, it
is easier to allow a white-flowered pea to
self-pollinate. Thus pollen from a white
flower fertilize ovules in a white flower.
Obviously, the whites are a pure line. Consider now the red-flowered plants: one third
of them turn out to be pure red-breeding.
When crossed with each other, or when
you permit self-pollination, they produce
only red-flowered plants, just like grandfather. The other two-thirds of the second
generation reds are like father and
mother—hybrid red—because upon interbreeding they give a 3 to 1 ratio of red to
white. So you see we have actually three
kinds: pure red, hybrid red, and white. And
the ratio between the kinds is 1:2:1. Gelt?
[Mendel suddenly notices a stem with
pink flowers. He picks it up.] Ach du Lieberl
Was ist das} Pink flowers? They should be
only red or white! [He tosses the pink flowers away.] I think that some student has
played a trick on Pater Mendel. Alsol I began
to think of discrete hereditary units. I called
them Elemente. They pass from generation
to generation through the pollen grains
and the ovules. Now there must be an Element for whiteness, a recessive, and a dominating Element for redness. When they are
together in a hybrid, the flowers are red.
But the Element for whiteness is there, all
the time. It will not be lost or contaminated. I then devised a simple system for
recording the Elemente, to save much writing. I said let the letter A represent an
Element for flower color with capital A
standing for the dominating Element and
little a for the recessive Element. Now hybrid
red, because it has both Elemente, should
be expressed by Aa. When the hybrids produce pollen and ovules the Elemente separate from one another so that in the stamens two kinds of pollen grains are formed,
half of them possessing large A and half of
them little a. Likewise in the pistil two types
of ovules will develop: those with A and
those with a. Gelt} This separation of the
Elemente I called the law of segregation.
You must understand that I was not the
first person to study inheritance. Men and
751
women have been breeding plants and animals since ancient times and some scientists
have tried to discover the principles of
heredity. But why did I succeed whereas
others failed? One reason is just this: I
selected a few features with well-defined,
contrasting traits to study in an organism
that was suitable for experimentation. My
predecessors, however, tried to study the
whole organism at once. But inheritance is
complex. One must simplify the investigation, study one pair of contrasting traits
at a time. And then you may study two
traits together, as we shall do presently.
Only in that way can one discover the
secrets of nature. Then second, I used
quantitative methods. I counted peas, and
peas, and peas! I kept very careful records,
and I calculated ratios. During the long
winter months I worked with my seeds,
counting them, placing them in properly
labeled envelopes, posting my accounts,
doing the calculations, and planning the
experiments for the next spring. Hard,
tedious labor, but that was how I succeeded. I shall not say that my predecessors
were lazy. I was willing to work with zeal,
patience and with the stubbornness of my
peasant ancestry.
Also. Having studied all seven features
with clear contrasting traits and learning
that each one obeys the law of segregation,
I proceeded to study two or three features
simultaneously. Let me illustrate. Suppose
we cross a pure-breeding red-flowered, tall
pea plant with a white-flowered, short one.
Now we must choose a letter to stand for
length of vine, the second feature. Choose
letter B. Again the large B represents the
dominating Element for tall; the little b
stands for the recessive one for short. So
I write AABB x aabb. All of the first-generation offspring will be hybrid red and
hybrid tall or AaBb. Gelt} This follows from
the law of segregation.
Now let us cross two such hybrids or simply allow self pollination. I then discovered
my second principle, the law of independent assortment. That means the Elemente
for one feature (flower color) segregate
independently of the Elemente for the other
feature (length of vine). Thus there are
four types of pollen grains: AB, Ab, aB, and
752
'GREGOR MENDEL"
ab; and there are the same four types of
ovules. Next, we analyze the second-generation offspring. [Mendel uses a Punnett
square—an anachronism—to explain the
four phenotypes and nine genotypes and
their ratios. And with a table he demonstrates the arithmetic progression in numbers of gametes (pollen and ovules), phenotypes (traits), and genotypes (kinds), and
the combinations of gametes in crosses of
hybrids.]
Alsol What are these discrete Elemente
about which I have been speaking? I wish
I knew. My microscope does not greatly
magnify. I can see the tiny pollen grains
but not the Elemente inside them. I hope
that someday a powerful microscope will
be invented so that we can see the elements
of inheritance. And perhaps someday
clever chemists will be able to tell us their
chemical composition. Much more work
needs to be done on inheritance.
Recently I had a conversation with some
visitors in the monastery garden. One
member, a botanist, asked: "What is the
relationship, if any, between your work and
the origin of a new species?"
"I am convinced," I replied, "that my
studies on hybrids are of significance for
the evolutionary history of organic form."
They pressed me further. "Was I
acquainted with the writings of Charles
Darwin?" "Yes, indeed," I said. "I have
read almost everything that he has written
on the subject of evolution. Our monastery
library contains many of Darwin's books
and also Zoonomia by his grandfather, Erasmus Darwin."
"I have long thought that there was
something lacking in Darwin's theory of
natural selection. And I have also questioned the views of Lamarck. I once made
an effort to test the influence of environment on plants. I transplanted certain
plants from their natural habitat to the
monastery garden. Although cultivated
side by side with the form typical of the
garden, no change occurred in the transplanted form as a result of the change in
environment, even after several years.
Nature does not modify species in that way,
so some other forces must be at work."
My visitors then asked me about new
experiments that I was conducting. I sadly
looked about the garden. Not one of my
plants could be seen. All were gone. I have
become so burdened with the administration of the monastery that I no longer have
time for experiments. Much of my time
and energy is required to fight the state
government for money to educate my boys.
The government does not seem to realize
the importance of education. Maybe this is
your experience also. And I have become
discouraged. Few appear to know about my
work—not even Charles Darwin. But I take
comfort in the thought that science is always
moving forward, although slowly at times.
Sooner or later—sooner or later—my work
will be repeated, and I shall be either right
or wrong. In the meantime I must have
patience. I think that my day will come.
That is what I tell my boys. I say to them:
"Work hard, work with joy, and work with
patience. And I often commend to them
that verse in the Book of Ecclesiastes: "The
patient in spirit is better than the proud in
spirit. Therefore, be not hasty, and be not
angry: for haste and anger rest only in the
bosoms of fools." May God bless you.