A reconstruction of Mendel's Pisum experiments and an attempt at an explanation of Mendel's way of presentation


Orel, V.

Folia Mendeliana 6: 41-60

1971


R. A. Fisher (1936) in reconstructing Mendel's Pisum experiments had to come to the conclusion that Mendel knew very well what to expect. A new attempt at a reconstruction of Mendel's Pisum data yielded some differences in numbers and periodical arrangement of the experiments. This fully confirms Fisher's conclusion that Mendel must have known beforehand what to expect. It is, however, improbable that the hybridizing experiments preceded the experiments on gametic ratios as Fisher thought. It is most likely that after concluding (p. 29) "that pea hybrids form germinal and pollen cells that in their composition correspond in equal numbers to all the constant forms resulting from the combination of traits united through fertilization" Mendel projected his programme of hybridizing peas differing in one or more trait pairs to demonstrate how his idea worked. From the didactic point of view, he, however, first. described his mono-, di- and trihybridizing experiments which he presumed to be more easily comprehensible to his listeners. A detailed explanation of his theory was presented later in the letter, part "On Reproductive Cells" and especially in the Concluding Remarks.

A
RECONSTRUCTION
OF
MENDEL'S
FISUM
EXPERIMENTS
AND
AN
ATTEMPT
AT
AN
EXPLANATION
OF
MENDEL'S
WAY
OF
PRESENTATION
laterslav
Orel,
Mendelianum
of
the
Moravian
Museum,
Mendelovo
n.1,
Brno
An
Attempt
at
a
Reconstruction
by
R.
A.
Fisher
When
R.
A.
Fisher
/1936/
made
an
attempt
at
a
reconstruction
of
Mendel's
data
in
order
to
subject
them
to
statistical
analysis,
he
came
across
the
trouble
that
he
was
neither
able
to
make
a
complete
numerical
reconstruction
of
the
individual
experiments,
nor
to
ascertain
the
time
and
the
sequence
order
of
the
individual
experiments.
He
arrived
at
the
following
conclusion:
"Mendel
was
an
experienced
and
successful
teacher,
and
might
well
have
adop-
ted
a
style
of
presentation
suitable
for
the
lecture
-room
without
feeling
under
any
obligation
to
complicate
his
story
by
unessential
details".
This
is
confirmed
by
Mendel
himself
in
his
second
letter
to
Ntigeli
of
April
18th,
1867,
which
was
most
probably
unknown
to
R.A.Fisher,
where
he
writes
about
his
work:
"The
paper
which
was
submitted
to
you
is
the
unchanged
re-
print
of
the
draft
of
the
lecture
mentioned;
thus
the
brevity
of
the
exposition,
as
is
essential
for
a
public
lecture".
Mendel
was
successful
in
the
presentation
of
his
experiments
even
though
his
listeners
in
Brno
did
not
understand
much
of
him,
and
could
not
have
understood
him
in
Fact.
Fisher's
characterization
comes
very
near
to
the
truth:
°Mendel'
s
paper
is,
as
has
been
frequently
noted,
a
model
in
respect
of
the
order
and
lucidity
with
which
the
successive
relevant
facts
are
presented,
and
such
orderly
presentation
would
be
much
facilitated
had
the
author
felt
himself
at
liberty
to
ignore
the
particular
crosses
and
years
to
which
the
plants
contributing
to
any
special
result
might
belong".
In
his
reconstruction
Fisher
/1936/
used
only
the
data
from
Mendel's
published
paper
without
making
use
of
other
information
about
the
experi
-
ments
Mendel
mentioned
in
his
letters
to
Ntigeli,
what
was
also
pointed
out
by
Bennett
/1965/
and
later
also
by
Weiling
/1970/.
For
the
sake
of
a
better
understanding
of
Mendel's
approach
in
organizing
his
experi
-
ments
and
his
way
of
presenting
their
results
it
could
be
worthwhile
to
make
a
new
attempt
at
a
reconstruction
of
the
Pisum
experiments
on
the
basis
of
all
accessible
sources.
The
first
part
should
investigate
the
probable
dating
of
the
individual
experiments,
out
of
which
the
entire
system
of
work
will
result.
Last,
but
not
least,
along
with
this
goes
the
question
of
the
claim
of
the
space
in
connection
with
the
experiments
because
of
the
small
size
of
the
experimental
garden.
A
new
attempted
reconstruction
of
Mendel's
hybridizing
experiments
seems
to
be
promising
for
penetrating
rather
profoundly
into
Mendel's
way
of
thinking
when
creating
his
idea,
designing
his
experiments
and
especially
when
writing
his
famous
Pisum
paper.
Experimental
period
In
his
paper,
Mendel
mentioned
in
the
chapter
"The
subsequent
generations
from
hybrids"
describing
the
descendants
of
the
monohybrids
on
page
17:
"Experiments
1
and
2
have
by
now
been
carried
through
six
generations,
3
and
7
through
five,
and
4,5
and
6
through
four
with-
out
any
deviation
becoming
apparent,
although
from
the
third
generation
on
a
small
number
of
plants
were
used".
This
led
Fisher
to
the
assumption
that
Mendel
had
started
his
experi-
ments
in
1857.
In
his
second
letter
to
NtIgeli
of
April
17th,
1867,
Mendel
gave
the
period
of
experiments
with
Pisum
as
follows:
"the
experiments
which
are
discussed
were
conducted
41
SCHEME
OF
MONOHYBRIDISM
GIVING
THE
DATA
FROM
THE
FIRST
EXPERIMENT
Fi
9
.
I
P
A
a
F
3
A
F2
H
A
a
25.5
'
S
.7324,
-
-
- - -
- - -
•S
.5474
r
1
r
--
1
2k
I
S•4850
-
L'
_
_
_
_
_
I
;Aka
-
1
7
Aa
r
Aa
a
a
a
from
1856
to
1863".
In
a
further
part
of
the
letter
it
runs:
"at
that
time
En
.1863]
they
were
terminated
in
order
to
obtain
space
and
time
for
the
growing
of
other
experimental
plants".
In
the
given
second
letter
Mendel
also
mentioned
the
number
of
experimental
plants
in
the
individual
generations
as
follows:
"For
two
generations
all
experiments
were
conducted
with
a
fairly
large
number
of
plants.
Starting
with
the
third
generation
it
became
necessary
to
limit
the
numbers
because
of
lack
of
space,
so
that,
in
each
of
the
seven
experiments,
only
a.
sample
Cn
the
German
original
it
runs:
nur
einzelne
von
jenen
Pflanzeg
of
those
plants
of
the
second
generation
/which
either
bred
true
or
varied/
could
be
observed
fur-
ther.
The
observations
were
extended
over
four
to
six
generations
/p./7/.
Of
the
varieties
which
bred
true
/p.19
-
21/
some
plants
were
observed
for
four
generations".
To
this
in-
formation
attention
is
paid
also
by
Weiling
/1970/.
Monohybrid
Experiments
From
the
given
Mendel's
data
it
is
possible
to
reconstruct
the
time
sequence
of
the
first
seven
experiments
with
Pisum
differing
in
one
trait
pair.
The
first
experiment
with
crossing
peas
differing
in
the
shape
of
the
ripe
seeds
is
given
in
Fig.
1.
Fig.
1
demonstrates
also
the
character
of
further
monohybrid
experiments.
The
rectangles
drawn
in
a
full
line
in
F
i
and
F
2
represent
the
phenotypical
categories.
The
rectangles
drawn
in
a
thin
dashed
line
represent
the
genotypic
categories.
The
scheme
also
gives
the
number
of
experimental
plants
/p/,
or
seeds
/s/,
respectively.
The
hybrids'
progeny
marked
from
F
1
to
F
4
according
to
Mendel's
original
indication
saying:
"die
erste,
zweite,
etc.
Generation
der
Hybriden".
According
to
him
F
l
represents
the
F
2
Generation
in
current
genetical
terminology.
In
his
monohybrid
experiments
Mendel
observed
the
traits
of
seeds
and
plants.
In
the
first
case
he
could
observe
the
traits
of
fertilized
seeds
of
the
following
generation.
In
the
second
case
he
had
to
sow
the
fertilized
seeds
in
the
following
year
so
that
he
might
observe
the
germinated
plants.
When
reconstructing
the
experiments,
it
is
necessary
to
estimate
the
number
of
plants
Mendel
used
for
testing
the
constant
segregated
forms.
In
the
beginning
of
the
chapter
"The
second
generation
from
hybrids"
Mendel
states
only
/p.15/
:
"Those
forms
that
receive
the
recessive
character
in
the
first
generation
do
not
vary
further
in
the
second
with
respect
to
this
trait;
they
remain
constant
in
their
progeny".
If
we
consider
the
above
mentioned
data
in
Mendel's
second
letter
to
Islageli,
saying
Mendel
tested
constant
and
segregating
forms
already
from
the
third
generation
on,
then
his
only
some
plants
may
well
comprise
even
less
than
50
plants
as
Fisher
/1936/
estimated
for
testing
only
segregating
forms.
As
the
cultivation
of
plants
was
limited'
in
the
Monastery
garden,
the
given
scheme
considers
only
20
plants
for
testing
recessive
homozygotes
in
F
2
.
The
concordant
number
of
20
plants
was
estimated
for
testing
the
dominant
homozygotes
and
20
plants
"which
varied",
i.e.
he-
terozygous,
starting
with
the
third
generation.
This
foreshadows
Mendel
did
not
test
con-
stant
forms
segregation
in
further
generations
of
hybrids
x/
progeny.
x/
If
he
had
tested
further
segregation
of
homozygous
recessive
as
well
as
dominant
forms,
he
must
have
tested
further
segregated
recessive
homozygotes
in
F
2
and
in
each
succeed-
ing
generation
always
two
more
groups.
In
the
first
and
second
experiments
this
would
mean
300
more
plants,
in
the
third
and
seventh
experiments
120
more
plants
and
in
the
fourth
to
sixth
experiments
60
more
plants,
that
is
480
plants
altogether.
Considering
the
fact
that
Mendel
evidently
tested
only
constant
forms
in
di-
and
trihybrid
experiments,
it
is
more
probable
that
in
the
monohybrid
experiments
he
limited
his
experiments
only
to
the
extent
given
above.
43
The
numbers
of
the
individual
experimental
plants
from
all
seven
experiments
are
given
in
Table
1.
The
Table
estimates
the
first
two
experiments
started
in
1856.
This
is
evident
from
Mendel's
data
in
his
second
letter
to
NAgeli,
saying
the
experiments
were
opened
in
.
that
year.
Fisher,
as
given
above,
estimated
the
beginning
of
those
experiments
one
year
later
because
he
considered
only
six
generations
of
the
hybrid's
progeny
given
in
Mendel's
paper.
In
evaluating
the
experiments
with
germ
cells
Mendel
was
aware
of
the
fact
/see
his
paper
on
p.
31/
that
"the
larger
their
number
[of
plants
or
seeds]
,
the
more
likely
it
is
that
mere
chance
effects
will
be
eliminated".
For
this
reason
Mendel
increased
the
number
of
plants
in
the
hybrids'
progeny
four
times,
The
Table
gives
also
the
number
of
artificial
fertilizations
Mendel
carried
out.
In
his
first
two
experiments
the
highest
number
of
118
artificially
fertilized
plants
is
given,
which
must
have
been
a
very
laborious
work.
If
we
consider
that
in
1856
Mendel,
besides
his
teaching
activity,
was
studying
for
his
university
exam,
we
can
presume
that
he
did
not
make
another
169
experiments
with
artificial
fertilization
in
this
year.
In
the
following
experiments
we
can
presume,
similarly
to
Fisher,
the
beginning
according
to
Mendel's
data
on
the
number
of
generations
of
the
hybrids'
progeny
cultivated
until
1863.
Accord-
ing
to
this,
the
third
and
seventh
experiments
might
have
been
started
in
1857,
while
the
remaining
ones
one
year
later.
In
this
connection
attention
may
be
drawn
to
a
certain
source
of
information
on
the
green
-house
erection
Mendel
mentions
on
page
9.
According
to
the
"Stifts-Haupt
Kassa
Journal"
/Nat.Arch:Brno,
Collection
E
-
4/
a
new
green
-house
was
built
near
the
experimental
garden
in
1855,
which
was
officially
approved
on
August
30th,
1856.
The
old,
perhaps
very
small,
green
-house
was
situated
in
the
garden
beyond
the
church.
According
to
this
fact
Mendel
might
have
used
the
new
green
-house
for
his
experi-
ments,
especially
from
1857
onwards.
In
his
experiments
with
plant
traits
/the
third
to
seventh/
Mendel
does
not
give
the
number
of
hybrid
plants.
Fisher
estimated
approximately
the
same
number
of
250
plants
as
given
by
Mendel
in
the
first
two
experiments.
In
Table
1
we
give
a
reduced
number
of
100
plants
on
the
basis
of
the
fact
that
Mendel
also
reduced
the
number
of
artificial
ferti-
lizations
from
the
average
59
in
the
first
two
experiments
to
33.6
in
the
remaining
experi-
ments.
Even
when
using
100
plants
Mendel
had
three
times
as
much
the
necessary
number
of
seeds
to
be
sown
in
the
succeeding
generation.
In
his
experiments
with
plant
traits,
Mendel
/see
p.16/
tested
the
constant
character
in
the
hybrid's
progeny
with
dominating
trait
in
such
a
way
that
"100
plants
that
possessed
the
dominating
trait
in
the
first
genera-
tion
were
selected,
and
in
order
to
test
this
trait's
significance
10
seeds
from
each
plant
were
sown".
On
the
basis
of
this
fact
we
give
in
the
Table,
similarly
to
Fisher,
1,000
tested
plants.
It
is
necessary
to
consider
here
the
fact
that
all
seeds
did
not
germinate.
The
numerical
data
from
Mendel's
bifactorial
experiment
prove
a
germination
of
95.2
per
cent.
It
is
evident
that
950
plants
grew
enough
to
be
studied
in
each
experiment.
In
the
fifth
experiment
with
the
lowest
number
of
fertilization
and.
of
plants
germinated
from
the
hybrid
seeds,
Mendel
repeated
the
test
of
the
constant
dominating
trait,
because
the
orig-
inal
result
/p.16/
"showed
the
greatest
deviation"
from
the
expected
ratio.
In
Table
1
numbers
of
plants
for
artificial
fertilization
are
comprised
which
Mendel
gives
on
page
9.
However,
Mendel
states
here
also
that
"from
a
fairly
large
number
of
plants
of
the
same
kind
only
the
most
vigorous
were
chosen
for
fertilization",
It
is
evident
44
NUMBERS
OF
PLANTS
IN
MONOHYBRID
PISUM
EXPERIMENTS
TABLE
I
..
>t
,.)Ncp
1
2
3
4-
5
6
7
TO
T
A
1_
1856
15"%t
10
.20
)1
25°
5
°'
1857
253
258
10"Its
°
t
`
2
%
5
3
1f
4
°'
1858
56
5"ri
519&
2
°'
100
r
10"14
Th
10
20
100
1309°
9
°
1859
60
60
929
100
100
100
1064
2413
1860
60
60
10061
11
8
1
580
858
10&
4739'
40
'
1861
60
60
60
1000
1000
4
1000
60
3240e"
1862
60
60
60
60
1008
3
60
60
13
6
0"°'
1863
60
60
60
60
60
300
TOTAL
1
0730)
1020)
221g
0)
244
27fra
2048
2
3
/
1
139170.4
NUMBER
OF
[ARM
LY
OBSERVED
PLANTS
25
531
1109
1993
2619
+
ADDITIONAL
PLANTS
FROM
WHICH
A
HALF
OF
THE
MOST
VIGOROUS
WERE
CONSIDERED
FOR.
FERTILIZATION
ac
NUMBER
OF
ARTIFICIAL
FERTILIZATIONS
NUMBERS
OF
PLANTS
IN
PISUM
EXPERIMENT
TABLE
2
Exp.
ea
Pore
lines
mono-
hybrids
di
-
-
hybrids
fri
-
hyb
r
id
s
9
erm
ce
ll
s
TOTAL
1854
850
850
55
850
850
56
550
25
(+5°
5756-50'
57
550
53
P
al
1081
144°)
58
550
1309
°
1
,,
30
30
1919
(+9°)
59
550
2413
15
24
3002
1860
550
4739
01
529
639
6457
(.40)
61
550
324d
+4
80
4738
°
860r
o)
62
550
1360
42°)
80
160
100
2250"
°)
63
550
300
80
160
i
551
1641
TOTAL
610013917,
814
5
-
7
1
3,
0:
651
27225
Plants
carefully
observed
25
531
1129
2032
3787
4730
50
551
12835
45
BIFACTORIAL
EXPERIMENT
Fig.
2
0
AB
ab
\
O
/
G1
315
AB
ABb
AaB
AaBb
38
65
60
138
H
AaBb
aBb
101
28
68
15p
108
A6
Aab
35
67
TRIFACTORIAL
EXPERIMENT
Fi9.3
ABC
ABC
ABc
A
bC
A
bc
aBC
aBc
a
bC
abc
1
10
H
abc
AaBbCc
687s
ABCc
AbCc
aBCc
abCc
ABbC
ABbc
aB
be
aBbc
AaBC
AaBc
AabC
Aabc
22
17
25
20
15
,
1$
19
24
14
18
20
16
24
p
AB
bCc
45
aBbe
aBbCc
AaBCe
AabCc
AaBbx/49
C
AaBbc
4
8
36
38
47
that
he
must
have
sown
a
larger
number
of
seeds,
e.g.
three
times
as
much,
i.e.
140
seeds
more.
Yet
it
is
a
small
number
out
of
the
total
of
14,077
plants
given
in
Table
1.
These
higher
estimates
of
plants
are
comprised
in
Table
2
in
the
total
estimate
of
tested
Plants.
Bi-
and
Trifactorial
Experiments.
Mendel
does
not
give
any
data
in
his
paper
according
to
which
we
might
date
his
bi-
or
trifactorial
experiments
in
the
period
of
1856
-
1863.
From
the
given
second
letter
to
NAgeli
one
can
deduce
that
in
1863
some
plants
were
observed
which
bred
true
or
varied
over
four
to
.
six
generations
for
the
last
time.
This
date,
to
which
Welling
/1970/
drew
attention,
es-
caped
Fisher's
attention
and
that
is
why
he
supposed
the
experiments
had
been
started
as
late
as
in
1861
in
accordance
with
the
smallest
claim
of
space
for
the
experimental
garden
in
1861
-
1863.
Figure
2
represents
the
scheme
of
the
bifactorial
experiment.
Mendel
gives
only
15
hy-
brid
plants
out
of
which
he
got
four
phenotypical
seed
categories.
The
estimate
of
plants
for
reciprocal
crossing
amounts
to
30
so
that
"only
the
most
vigorous"
could
be
'chosen
for
fer-
tilization
as
Mendel
states
in
his
paper
on
page
9.
In
the
trifactorial
experiment
30.
plants
for
fertilization
are
also
estimated.
Furthermore,
Mendel
gives
the
number
of
the
germinated
seeds
in
which
he
tested
genotypes
of
the
obtained
various
phenotypical
categories.
Out
of
556
seeds
he
planted
529
plants,
i.e.
95.2
per
cent.
In
Table
2
numerical
data
from
all
experiments
are
given.
The
beginning
of
the
bi-
and
trifactorial
experiment
is
according
to
Welling
/1970,
p.78/
estimated
in
1858
or
1859.
Figure
3
gives
the
trifactorial
experiment.
As'
far
as
numerical
data
are
concerned,
this
experiment
is
numerically
not
extent,
but
according
to
Mendel's
statement
on
pt4e
21
it
"required
the
most
time
and
effort"
.
Only
24
hybrid
plants
are
given.
Out
of
687
seeds
of
eight
pos-
sible
phenotypical
categories
Mendel
got
639
plants
/i.e.
93
per
cent/
in
the
following
year
of
27
possible
genotypical
categories.
The
constancy
of
the
third
trait
-
the
seed
coat
colour
-
Mendel
could
test
only
one
generation
later
than
that
of
the
first
two.
If
he
had
consistently
tested
the
constancy
of
the
third
trait
as
well
as
he
gives
in
his
monofactorial
experiment
for
four
generations,
then
he
might
have
started
his
trifactorial
experiment
one
year
earlier
than
the
bifactorial
experiment.
In
that
case
he
must
have
tested
the
given
4,730
plants
al-
ready
in
1860
when
he,
according
to
Table
2,
tested
the
largest
number
of
plants
from
his
monofactorial
experiments.
Because
of
the
space
limit
of
his
experimental
garden
it
is,
how-
ever,
not
very
probable.
Table
2,
therefore,
supposes
artificial
fertilization
in
the
trifactor-
ial
experiment
and
bifactorial
as
well.
In
the
second
generation
of
the
hybrids
Mendel
might
have
tested,
besides
the
constancy
of
the
trait
C,
already
four
constant
traits
with
recessive
c
known
to
him,
namely:
ABc,
Abc,
aBc,
abc.
In
the
following
years
testing
of
all
eight
constant
forms
is
supposed
in
20
plants
each.
Experiments
on
the
Reproductive
Cells
of
Hybrids
I
did
not
succeed
in
finding
any
data
enabling
to
date
the
experiments
on
the
reproduction
cells
of
hybrids.
Their
schemes
are
given
in
Fig.
4
to
6.
Mendel
does
not
say
the
number
of
plants
and
fertilization
either
of
the
original
generation
or
in
crossing.
It
is
highly
evi-
dent
that
he
did
not
carry
out
special
fertilization
to
obtain
the
original
genotypical
cate-
gories
AaBb,
Aab
and
aBb,but
that
he
used
seeds
material
from
other
experiments.
In
re-
ciprocal
crossing
20
plants
are
estimated.
Mendel
only
says
on
page
25
that
"the
most
vigorous
specimens
were
chosen
for
reciprocal
crosses".
The
data
on
the
number
of
plants
48
o
AB
ab
AaBb
O
O
AaBb
AB
O
AB
ABb
AaB
AaBb
22
EXPERIMENTAL
TESTING
OF
THE
HYPOTHESIS
Fici.
5
AB
O
0
AaBb
O
AaBb
O
AaBb
ab
Aab
aBb
e,"
Ab
N
s
Fi43.
6
0
Aa6
aB
ab
o
aBb
0
AaBb
115
41
57
Aab
147,
a
aBb
O
aBb
40
Aab
5,
79
are
given
in
Table
3.
Their
total
number
is
comprised
in
Table
2.
Table
3
-
Number
of
Plants
Tested
in
the
Experiment
on
Germ
Cells
Type
of
crossing
Number
of
Plants
for
fertilization
hybrids
AaBb
x
AB
/20/
x
90
AB
x
AaBb
/20/
110
AaBb
x
ab
/20/
87
ab
x
AaBb
/20/
98
Aab
x
aBb
/20/
166
Total
100
551
x/
estimate
These
experiments
did
not
require
much
garden
space
and
Fisher
assumed
that
Mendel
carried
them
out
in
1861
-
1862.
In
this
reconstruction
they
are
dated
back
to
1862
and
1863.
Out
of
the
total
number
of
experimental
plants
it
is
the
smallest
number,
and
estimates
of
(
the
probable
time
period
they
were
carried
out
in
can
be
only
of
a
speculative
character.
The
Total
Number
of
Experimental
Plants
Next
to
the
tested
plants
described
in
the
experiments,
Mendel
also
multiplied
34
and
later
22
varieties
of
peas
proved
as
being
pure..
Fisher
estimated
the
number
of
multiplied
plants
as
60
for
each
variety.
In
Table
2
only
half
the
number
is
considered,
because
Mendel
must
have
been
very
much
limited
by
the
space
available
in
the
garden
and
the
green
-house.
Moreover,
he
made
further
experiments
he
mentions
only
by
the
way.
In
describing
the
fifth
experiment
he
says
in
the
footnote
/p.8/
:
"One
variety
has
a
beau-
tiful
brownish
-red
pod
colour
which
tends
to
a
violet
and
blue
around
the
time
of
ripening.
The
experiment
with
this
trait
was
started
only
in
the
past
year".
This
footnote
shows
that
the
fifth
experiment
was
at
least
carried
out
in
more
varieties
of
peas
and,
moreover,
was
not
started
in
the
same
year.
Otherwise
we
would
have
to
accept
the
statement
that
he
start-
ed
his
experiments
later
than
he
said
in
his
paper
on
page
17,
when
describing
the
genera-
tions
tested
for
constancy.
In
the
second
letter
to
Nageli,
Mendel
mentions
the
tetrahybrid
crossing
which
Welling
/1970/
assumes
was
carried
out
in
1857
at
the
latest.
The
obtained
'descendant
BcDG
ex-
hibited
good
qualities
and
Mendel
planted
it
in
the
vegetable
garden
for
current
use.
Men.del's
last
statement
on
page
23
has
escaped
attention
till
now:
"All
constant
associ-
ations
possible
in
Pisum
through
combination
of
the
above
-mentioned
seven
characteristic
traits
were
actually
obtained
through
repeated
crossing.
Their
number
is
given
by
2
7
=128".
Some
of
these
associations
are
mentioned
by
Correns
/1905/
in
the
appendix
to
the
second
letter
to
Nagel"
in
the
description
of
140
seed
parcels.
In
the
English
and
Russian
editions
of
Mendel's
letter
to
Nageli
this
appendix
is
not
given.
Similarly
on
page
24,
Mendel
mentioned
"an
experiment
of
flower
stems
of
different
lenght
gave
on
the
whole
rather
satisfactory
results,
although
distinction
and
classification
of
the
50
Fi9.7
A
POSSIBLE
LAY
-OUT
OF
PLANTS
IN
THE
MENDEL
EXPERIMENTAL
GARDEN
The
dots
represent
the
plants
the
total
number
of
which,
Uxy.
is
expressed
by
Uxy
-
2n
im4
-
1);
where
m,n
are
integral
parts
of
divisions
a/x,
1)/y
respectively
and
y
y
1
+
y
2
.
a
-
7',,
rr.
5.
0-
*
forms
could
not
be
accomplished
with
the
certainty
that
is
indispensable
for
correct
experi-
ments".
This
supports
the
assumption
that
Mendel
planted
further
plants
we
have
no
evidence
of.
In
Mendel's
paper
the
total
number
of
tested
plants
is
given
only
on
page
10:
"more
than
10,000
carefully
examined
plants
...".
Out
of
the
total
number
of
estimated
plants
given
in
Table
2
it
is
necessary
to
deduct
the
plants
which
were
not
carefully
examined.
These
are
the
plants
of
pure
varieties
first
of
all.
Further
hybrid
plants
of
the
third
to
the
seventh
mo-
nofactorial
experiments,
the
plants
tested
for
constancy
and
segregation
of
traits
from
the
third
generation
of
the
hybrids'
progeny
on.
Also
plants
tested
for
constancy
of
dominating
traits
in
the
third
generation
in
monofactorial
experiments
might
not
have
been
carefully
ex-
amined.
Neither
are
the
plants
estimated
in
Table
2
for
fertilization
listed.
In
Tables
1
and
2,
in
the
last
column,
estimates
of
"carefully
examined"
plants
are
given
separately.
Their
total
number
of
12,835
plants
given
in
Table
2
approaches
Mendel's
given
number
of
"more
than
10,000
carefully
examined
plants".
Estimates
of
Number
of
Observed
Seeds
The
exactness
of
Mendel'
s
work
is
also
characterized
by
the
number
of
seeds
examined.
First
of
all
he
had
to
observe
the
seeds
from
the
first
two
monofactorial
experiments
in
2,140
plants
and
most
probably
also
the
seeds
from
the
third
experiment
in
which
he
exam-
ined
flower
and
seed
-coat
colours.
Further,
all
seeds
from
the
bi-
and
trifactorial
experi-
ments
and
lastly
the
seeds
from
the
experiments
on
the
germ
cells
.
Out
of
the
total
number
of
11,482
plants
he
obtained
on
the
average
30
x/
seeds
per
plant,
i.e.
344,460
seeds
altogeth-
er.
Experimental
Plants
and
the
Size
of
the
Garden
Plot
On
page
9,
Mendel
says
that
"the
plants
were
grown
in
garden
beds
-
except
for
a
few
in
pots
-
and
were
maintained
in
their
natural
upright
position
by
means
of
sticks,
twigs,
and
taut
strings.
For
each
experiment
a
number
of
the
potted
plants
were
placed
in
a
green-
house
during
the
flowering
period;
they
were
to
serve
as
controls
for
the
main
experiment
in
the
garden
against
possible
disturbance
by
insects".
R.A.
Fisher
/1936/
gives
in
the
footnote
of
his
account
on
the
possible
number
of
culti-
vated
plants
in
the
Monastery
garden
a
communication
by
Rasmussen
/
Sweden/
that
Mendel
might
have
grown
4,000
-
5,000
plants
in
the
experimental
garden
the
area
of
which
was
7
by
35
metres.
A
possible
setting
of
plants
in
Mendel's
garden
is
demonstrated
in
Fig.
7.
If
we
consider
paths
of
40
cm,
the
spacing
between
two
rows
making
20
or
15
cm,
and
the
distance
between
the
plants
in
the
row
being
20
or
15
cm,
Mendel
might
have
grown
3,503
-
5,043
plants
in
his
garden,
which
is
in
agreement
with
Rasmussen's
estimated
number
of
grown
plants
.The
estimated
manner
of
growing
peas
is
in
accordance
with
Mendel's
manner
of
harvesting
seeds
from
the
examined
plants
in
the
garden.
In
his
second
letter
to
Niigeli,
Mendel
writes
:
"The
legend
which
I
have
added
to
the
packet
numbers
on
a
separate
sheet
is
a
copy
of
the
notes
x/
In
the
most
extent
trifactorial
experiment
Mendel
obtained
on
the
average
28.6
seeds
per
plant.
52
I
made
for
each
individual
plant,
with
pencil,
on
its
envelope
at
the
time
of
harvest".
The
estimated
way
of
the
harvest
gives
evidence
for
an
easy
access
to
all
plants.
If
we
consider
a
part
of
the
plants
Mendel
grew
in
his
green
-house
and
some
in
the
veg-
etable
garden,
we
can
presume
that
the
numerical
estimate
and
the
estimate
of
the
time
se-
quence
order
of
the
experiments
given
in
Table
2
may
well
come
near
the
truth.
Impetus
to
Mendel's
Research
Programme
The
plant
and
animal
breeders
in
Moravia
of
the
nineteenth
century
were
highly
interested
in
breeding
new
breeds
and
sorts
and
the
applied
methods
of
crossing
and
hybridization
were
described
in
books
on
agriculture.
When
studying
theology,
Mendel
was
reading
special
courses
in
agriculture
and
pomiculture
and
vine
-growing
given
by
his
Professor
F.Diebl
/1770
-
1859/
who
devoted
attention
to
those
problems
in
several
publications
of
him
as
treat-
ed
in
the
previous
Colloquium
paper
by
Orel,
Rod
and
Vcivra.
Mendel
possessing
both
practical
and
theoretical
knowledge
in
plant
breeding
could
start
his
Pisum
experiments
only
on
the
basis
of
his
experience
he
gained
from
his
previous
ex-
periments
as
given
in
his
paper.
In
his
fourth
letter
to
Nageli
of
February
9th,
1868,
Mendel
wrote:
"After
having
in
the
past
two
years
collected
some
experience
in
the
artificial
fertilization
of
Hieracia,
I
intend
to
perform
some
planwise
experiments
with
this
genus".
This
gives
some
evidence
for
the
fact
that
Mendel
might
similarly
have
collected
experiences
with
hybridization
of
Pisum
be-
fore
projecting
those
treated
in
his
Pisum
paper.
When
studying
at
the
University,
Mendel
purchased
a
book
by
C.F
.
Gartner
/1849/
"Versuche
und
Beobachtungen
fiber
die
Bastard-
erzeugung
im
Pflanzenreich"
which
is
now
in
the
Mendel
Archives
in
Brno.
Frequent
under-
lining
and
notes
by
Mendel
allow
us
to
assume
that
he
must
have
read
it
from
cover
to
cover.
In
the
text
of
Gartner's
book
Mendel
marked
in
his
typical
manner
interesting
parts
of
the
text
and
on
the
inner
side
of
the
book
cover
he
made
some
notes,
e.g.
extracts
from
the
text
or
numbers
of
pages
which
drew
his
attention.
On
the
inner
side
of
the
front
cover
we
can
read,
e.g.
"499
Pisum".
On
the
inner
side
of
the
back
cover
there
are
also
notes
on
trait
pairs
of
Pisum,
on
the
one
side,
and
traits
of
Geum,
Aquilegia
and
Verbascum
and
numbers
of
pages
on.
the
other
side.
When
studying
Gartner's
book,
Mendel
must
have
come
across
the
explanation
of
the
uni-
formity
of
hybrids
and
with
extreme
diversity
of
forms
in
the
second
and
succeeding
genera-
tions.
Gartner
also
stated
that
both
parental
forms
and
completely
new
ones
appeared
in
the
hybrids'
progeny.
To
these
facts
attention
was
brought
also
by
Zirkle
/1951/
and
by
Welling
/1970/.
Hence
one
can
say
that
Gartner
described
separately
all
phenomena
that
occur
in
the
definition
of
the
so-called
Mendel's
laws
of
heredity
with
the
exception
of
the
numerical
segregation
ratio.
In
Gartner's
book
Mendel
marked
the
text
he
must
have
been
interested
in
in
his
medita-
tions
preceding
the
experiments
.
Furthermore,
some
parts
of
the
text
are
marked
which
might
have
had
some
connection
with
the
creation
of
his
idea
as
well
as
with
projecting
his
experi-
mental
plan.
On
page
235,
Mendel
e.g.
margined
a
part
of
the
text
dealing
with
hybrid
types:
"Dass
die
Typen
der
Bastarde
im
Allgemeinen
nicht
vag
und
zufallig
sind,
oder
aberhaupt
ganz
von
aus-
seren
Einfliissen
abhangen:
sondern
constant
und
gesetzmassig
aus
den
gleichen
Faktoren
immer
wieder
ebenso
gebildet
weraen,
kann
man
auch
noch
ganz
deutlich
aus
der
vollkom-
53
menen
Gleichheit
der
Produkte
der
Kreuzung
der
Arten
abnehmen".
This
might
have
initiated
Mendel's
statement
in
his
paper
he
made
on
page
11:
"...
it
is
entirely
immaterial
whether
the
dominating
trait
belongs
to
the
seed
or
pollen
plant".
On
page
272,
Mendel
margined
a
part
of
the
text
where
Gartner
initiated
to
analytical
search
for
a
law
of
the
origin
of
hybrid
form.
It
runs:
"...
so
machte
die
Analysirung
eines
Bastards
mit
einfacher
Organisation
and
geometrischer
Regelmassigkeit
des
Stengels,
der
Blotter
u.s.w.
in
seine
beiden
Faktoren
kein
ganz
vergeblicher
Versuch
sein;
nicht
nur
den
Gesetzen
der
Formbildung
der
Bastarde,
sondern
folglich
auch
der
Gewachse
iiberhaupt
auf
die
Spur
zu
kommen"
.
There
are
no
indications
foreshadowing
Mendel
might
have
got
any
impetus
from
the
authors
quoted
in
his
paper
with
the
exception
of
Gartner.
Mendel
refers
to
Kiilreuter,
Gart-
ner,
Herbert,
Lecoq
and
Wichura.
It
can
be
presumed
that
he
studied
only
the
work
of
Gart-
ner
/1849/
and
Wichura
/1853
and
1865/
.
The
same
conclusion
was
also
arrived
at
by
Wei
-
ling
/1970/.
With
the
works
of
the
other
authors
Mendel
was
acquainted
through
Gartner's
book.
There
are
many
reflections
whether
Mendel
was
aware
of
the
work
by
Goss
/1824/
and
Seton
/1824/
who
came
closest
to
the
observation
of
dominance
and
segregation
of
seed
colour
in
peas
as
it
was
suggested
e.g.
by
Dunn
/1965/.
Zirkie
/1951/
drew
attention
to
the
fact
that
Gartner,
in
his
review
of
literature
relating
to
plant
hybridization
cited
the
work
of
Knight
/1824/
on.
peas.
In
describing
the
outcome
of
his
various
pollinations
on
Pi
-
sum
sativum
viride
Gartner
wrote
on
page
85
that
those
results
agreed
essentially
with
those
published
by
Goss
and
Seton.
These
authors
are
not
quoted
by
Gartner
in
the
authors'
index.
Gartner
quoted
Knight's
/1824/
paper
on
page
734
as
follows:
"Transact
of
the
horticult.
Soc.
of
London,
Vol.V.
Fiirst
Frauendorf,
Allg.
Gartenzeit,
1834
x/
Nr.
27,
.p.213.
Now
we
can
prove
that
Is&ndel
must
have
been
aware
of
the
works
by
the
given
English
authors.
The
paper
by
Alexander
Seton
was
read
to
the
Horticultural
Society
of
London
on
August
20th,
1822.
John
Goss
read
his
paper
in
the
Society
on
October
15th,
1822.
Th.A.Knight's
/1824/
paper
was
read
in
the
above
Society
on
June
3rd,
1823.
Partly
it
was
a
commentary
on
the
work
of
Seton
and
Goss
.
Knight
described
the
facts
of
dominance
and
segregation,
but
did
not
make
any
comments
.
The
three
papers
were
published
in
the
same
book
,volume
five
of
the
Transactions
of
the
Horticultural
Society
of
London
in
1824.
Mendel
made
a
pencilled
note
on
the
work
of
Goss
and
Seton
in
the
margin
of
Gartner's
book
on
page
85
as
follows:
"Frauendo
Zeitg
1837.
pg.
213".
The
journal
cited
by
Gartner
is
the
Allgenleine
deutsche
Garten
Zeitung
xx/
published
by
the"Praktische
Gartenbau-Ge-
sellschaft"/Practical
Gardening
Society/
in
Bayern.
On
pages
213-214,
vol.
1837
there
is
an
article
"tJber
die
durch
kreuzende
Befruchtung
bewirkte
Veranderung
in
der
Farbe
der
Erbsen".
The
article
appeared
under
the
initial
"G".
This
article
is
a
mere
translation
x/
The
year
1834
is
probably
misquoted
and
should
read
1837.
xx
'
This
is
to
thank
Professor
E.
Lauprecht
for
his
kindness
in
providing
me
with
a
xero,
copy
of
this
work.
54
of
communications
by
Goss
and
Seton.
The
only
change
is
in
the
date
of
the
experimental
period.
The
reader
of
the
German
article
must
have
been
of
the
opinion
that
the
anonymous
author
described
his
own
experiments.
From
the
German
paper
Mendel
learned
the
uniform-
ity
of
pea
seeds
colour
of
hybrids
and
the
segregation
of
both
parental
forms
in
the
succeed-
ing
generation.
The
article
of
the
Bavarian
gardeners'
Journal
might
have
also
influenced
Mendel
in
that
sense
that
it
evoked
again
his
interest
in
hybridizing
experiments
with
the
view
of
obtaining
new
traits
of
cultural
plants,
e.g.
from
the
viewpoint
of
plant
breeding.
For
creating
and
supporting
his
idea
Mendel
might
have
taken
over
some
further
data
from
Gartner's
book.
Gartner
also
described
e.g,
on
page
290
the
character
of
dominance,
intermediarity
and
recessiveness,
even
though
he
did
not
use
terms
later
appearing
in
Mendel's
paper.
To
support
the
hypothesis
of
Mendel's
preceding
considerations
the
marked
text
on
page
260
is
of
interest:
"Aus
diesen
Verschiedenheiten
folgt,
class
sich
fiber
Blattbildung
der
Bastarde
aus
der
Form
der
Blatter
der
Stammeltern
noch
keine
bestimmte
Norm
auf-
stellen
lasst,
und
Bass
hiezu
noch
eine
grosse
Anzahl
von
Beobachtungen
und
Vergleichun-
gen
erforderlich
ist".
This
might
have
lead
Mendel
to
the
necessity
of
studying
the
regu-
larity
of
hybrids'
formation
in
a
larger
number
of
experimental
plants
-
as
Mendel
already
stated
in
the
Introduction.
On
page
311
of
Gartner's
book,
Mendel
margined
with
double
lines
the
text
proving
that
heredity
is
not
always
a
blending
process.
This
might
have
evoked
Mendel
for
searching
the
particular
character
of
factors
controlling
the
plant
forms.
In
the
first
part
of
his
lecture
Mendel
termed
the
plant
characters
as
symbols
in
capital
and
small
letters
and
much
later
in
the
second
lecture
when
explaining
his
theory
he
used
the
terms
Anlage
:
Faktor
and
Element.
He
also
underlined
the
term
Anlage
in
Gartner's
book
on
page
473
"...
so
sehen
wir
uns
veranlasst,
die.
Ursache
dieser
Abweichung
von
dem
gewohnlichentlmwandelungsprocess
in
einer
besonderen
Anlage
des
Eichens
zu
ver-
muthen,
welches
dem
lndividuum
seine
Entstehung
gab;
Worilber
jedoch
noch
weitere
Unter-
suchungen
anzustellen
sind".
Similarly
on
page
250
Mendel
margined
with
double
lines
the
text
on
elements
relating
to
traits.
"Die
Erklarung
der
Entstehung
und
Bildung
der
Formen
der
Bastarde
aus
den
Elementen
und.
Charakteren
der
Stammeltern
ist
fur
die
Pflanzenphy-
siologie
ebenso
wichtig
als
fiir
die
systematische
Botanik;"
Gartner
also
assumed
that
"Factor",
"Anlage"
and
"Element"
controlling
hybrid's
for-
mation
are
of
material
character.
On
page
271
Gartner
says
among
others:
"Das
weibliche
Element
ist
daher
unzweifelhaft
auch
bei
der
Bildung
der
Bastardtypen
thatig
und
der
mann-
liche
Befruchtungsstoff
nicht
das
allein
schaffende
bei
der
Bildung
/des
Embryo
und/
der
Typen
der
Pflanzenbastarde".
The
segregating
of
factors
/Trennung
der
Faktoren/
in
the
development
of
hybrid's
pro-
geny
are
also
mentioned
by
Gartner
on
page
446.Here
Mendel
might
have
found
the
idea
of
ele-
ments
segregation.
The
results
of
Mendel's
experimental
data
are
compared
by
him
in
the
Concluding
Re-
marks
only
with
Gartner's
and
secondarily
with
those
of
K5lreuter.
This
foreshadows
his
direct
precursor
was
Gartner.
Mendel
also
highly
appreciated
Gartner's
"very
estimable
observations"
already
on
first
page
of
his
Pisum
paper.
In
creating
his
idea,
Mendel
might
have
found
a
number
of
impetuses
in
Gartner's
book.
Nevertheless,
as
K31reuter's
and
Gartner's
successor
Mendel
must
have
had,
as
understood
55
by
de
Beer
/1965/
"a
flash
of
genius
of
his
own,
one
of
those
dangerous
things
called
ideas".
We
can
now
presume
that
after
his
return
home
from
his
studies,
Mendel
started
imme-
diately
some
preliminary
experiments
with
Pisum
varieties
he
had
brought
back
with
him
from
Vienna
already
with
that
intention,
as
he
later
stated
in
the
Introduction
to
his
Pisum
paper:
to
find
"generally
applicable
law
of
the
formation
and
development
of
hybrids".
From
his
paper
on
the
occurrence
of
Bruchus
pisi
/Verhandlungen
des
Zoologischen-botanischenVer-
eines
,
1854,
4:27-28/
it
can
be
confirmed
that
Mendel
occupied
himself
with
Pisum
experi-
ments
in
Brno
already
in
1853.
The
then
existing
interest
in
natural
science
in
the
Monaste-
ry
and
among
the
enthusiastic
natural
scientists
in
Brno
might
have
encouraged
Mendel
to
carry
out
his
programme.
From
the
published
Minutes
of
the
meetings
of
the
Natural
Science
Society
in
Brno
/Ver-
handlungen/
it
is
obvious
that
also
other
natural
scientists
in
Brno
displayed
great
interest
in
plant
hybrids
in
the
spirit
of
that
time.
In
the
very
beginning
of
the
Society's
activity
on
February
12th,
1862,C.
Theimer,
the
pharmaceutical
chemist
in
Brno,
reported
on
the
bastard's
forming
in
the
plant
kingdom
and
demonstrated
the
newly
found
bastard
Cirsium
praemorsum
Michl
/Cirs.
oleraceo-rivulare
Dc./
and•already
known
bastard
Cirsium
cano-
-oleraceum
Koch.
Theimer
characterized
the
parental
forms
by
that
of
the
bastard
in
de-
scribing
the
alternative
traits
of
the
leaves,
presence
of
thorns,
colour
of
blossoms,
po-
sition
of
stem
and
coverage
with
foliage
/Verhandlungen
des
nat.for.
Vereines
1862,
1:19-
-20/.
In
the
following
year,
on
July
7,
Profess'or
G.
Niessl
demonstrated
the
newly
found
bastard
Cirsium
palustri-rivulare
and
similarly
gave
in
detail
a
description
of
the
roots,
stems,
leaves,
and
blossoms
/Verhandlungen
des
nat.for.Vereines,
1863,
2:43-45/.
Next
year,
on
July
10,
Professor
A.
Makowsky
showed
the
honey
along
with
the
Italian
bee
and
the
bastard
between
/Verhandlungen
des
nat.for.Vereines,
1864,
3:60/.
On
➢ecember
14th
of
the
same
year
Niessl
reported
on
bastards
Hieracium
Auricula-Pilosella
Fries
and
Ver-
bascum
Lychnitidiphlomoid.es
Reissek
/Verhandlugen
des
nat.for.Vereines,
1864,
3:85-88/.
The
plant
hybrids
were
discussed
in
the
Natural
Science
Society
in
Brno
even
later
by
Mendel
as
well
as
by
other
Society
members
as
treated
in
detail
by
Ceti,
Character
of
experiments
In
his
first
lecture
in
1865
Mendel
first
read
the
empiric
results
of
his
experiments
with
crossing
organisms
differing
in
one
trait
pair.
Mendel
performed
these
monofactorial
experi-
ments
with
most
exactness
which
is
confirmed
by
the
fact
that
he
made
them
with
about
14,000
plants
out
of
the
total
estimate
of
about
21,500
plants
with
the
exception
of
the
number
of
plants
multiplied
as
pure
lines.
Most
conclusive
are
the
first
and
second
experiments
with
seed
traits
in
which
Mendel
tested
the
constancy
of
segregated
constant
forms
for
the
long-
est
time.
Intentiously
Mendel
said
on
page
19:
"Two
experiments
were
carried
out
with
a
larger
number
of
plants".
The
paragraph
closes
with
the
following
words:
"Experiments
with
seed
traits
lead
most
easily
and
assuredly
to
success".
In
these
first
experiments
Mendel
confirmed
in
two
years
the
uniformity
of
hybrids
and
at
the
same
time
he
proved
the
numer-
ical
segregation
ratio
3
:
1.
In
the
following
year
he
proved
the
segregation
of
constant
parental
forms
and
the
segregation
ratio
1
:
2
:
1.
Fisher
/1936/
suggested
that
Mendel's
discovery
of
"the
3
:
1
ratio
was
evidently
the
critical
point
in
his
research".
With
two
approximate
ratios
/meant
are
1
:
3
and
1
:
2
:
1/,
according
to
Fisher,
Mendel
was
"convinced
as
to
their
explanation,
and
framed
the
entire
Mendelian
theory
of
genetic
factors
and
gametic
segregation".
56
The
above
mentioned
ratios
Mendel
also
held
for
decisive
in
proving
his
theory.
This
can
be
seen
from
his
first
letter
to
Nageli.
He
did
not
expect
difficulties
in
proving
the
general
validity
of
this
theory
and
wrote:
"In
order
to
determine
the
agreement,
if
any,
with
Pisum,
a
study
of
those
forms
which
occur
in
the
first
generation
should
be
sufficient.
If,
for
two
differing
traits,
the
same
ratios
and
series
which
exist
in
Pisum
can
be
found,
the
whole
matter
would
be
decided",
It
can
be
deduced
that
Mendel
derived
or
confirmed
finally
his theory
after
the
evaluation
of
the
hybrid's
progeny
of
the
first
two
monofacto-
rial
experiments
at
the
latest
in
1858.
From
that
moment
on
all
experiments
ought
to
de-
monstrate
the
importance
and
sequence
of
his
theory.
In
contrast
to
Gartner's
data,
Mendel
newly
gives
the
regularity
of
numerical
segre-
gation
of
parental
and
hybrid
forms
in
the
hybrids'
progeny.
In
his
first
letter
to
Nageli
Mendel
regretted
that
Gartner
"did
not
diagnose
his
hybrid
types
sufficiently,
especially
those
resulting
frcim
like
fertilizations"
and
that
Gartner's
statements
"are
too
general,
too
vague,
to
furnish
a
basis
for
sound
judgment"
.A
novum
in
Mendel's
experiments
in
the
very
organisation
of
experiments
which
enables
to
form
"a
basis
for
sound
judgment".
Mendel's
original
idea
for
explaining
the
formation
and
development
of
hybrids
must
have
been
anticipated
by
the
hypothesis
according
to
which
the
experiments
were
projected
and
conducted.
This
hypothesis
Mendel
must
have
had
in
mind
already
when
describing
the
arrangement
and
sequence
of
the
experiments
on
page
9
as
follows:
"...
in
all
experiments
reciprocal
crosses
were
made
in
such
a
manner
that
that
one
of
the
two
varieties
serving
as
seed
plant
in
one
group
of
fertilizations
was
used
as
pollen
plant
in
the
other
group".
Mendel's
starting
point
lies
in
the
already
cited
experience
described
by
Gartner
on
page
222.
The
fact
of
equivalent
reciprocal
hybridization,
however,
was
not
proved
by
Mendel
theoretically
and
experimentally
until
in
his
second
lecture,
Chapter
on
"The
Reproduc-
tive
Cells
of
Hybrids"
in
explaining
his
theory
of
paired
elements.
It
is
also
remarkable
that
Mendel
does
not
give
numbers
of
tested
plants
for
recessive
constancy
segregated
in
the
hybrid's
progeny
in
his
monofactorial
experiments.
After
the
cited
second
letter
to
Nageli,
Mendel
studied
only
some
plants
"which
either
bred
true
or
varied".
This
is
possible
-to
explain
only
by
the
fact
that
at
that
time
Mendel
already
anti-
cipated
the
constancy
of
segregated
recessive
forms
in
evaluating
the
segregated
traits
in
the
hybrid's
progeny
as
factual
on
the
basis
of
gathered
previous
experience
and
also
on
the
basis
of
a
hypothesis
according
to
which
he
might
have
explained
numerical
segre-
gation
ratios
of
all
forms
in
the
hybrid's
progeny.
In
monofactorial
experiments
Mendel
demonstrated
series
in
hybrid's
progeny
and
thus
segregation
ratios.
The
possible
deviations
of
these
series
are
elucidated
in
jindra's
Colloquium
paper.
At
the
same
time
he
also
explained
the
principle
of
transformation
in
the
hybrid's
progeny.
In
the
bifactorial
experiment
he
illustrated
the
combination
series
composed
of
two
series
for
each
trait
pair,
and
in
the
trifactorial
experiment
he
genera-
lized
his theory
in
explaining
/p.22/
"that
constant
traits
occuring
in
different
forms
of
a
plant
kindred
can,
by
means
of
repeated
artificial
fertilization,
enter
into
all
the
as-
sociations
possible
within
the
rules
of
combination".
The
different
way
of
Mendel's
presentation
of
mono-,
bi-and
trifactorial
experiments
is
illustrated
in
Fig.
1,
2,
and
3.
The
arrangement
and
sequence
of
Mendel's
experi-
ments
along
with
his
careful
selection
of
pea
forms
for
crosses
and
his
way
of
different
evaluation
of
every
experiment
gives
evidence
for
the
assumption
that
Mendel
performed
57
those
experiments
to
demonstrate
the
significance
of
his
theory
just
according
to
the
plan.
Misra
/1965/
grasped
this
fact
as
follows:
"He
had
a
clear
idea
of
what
he
had
set
out
to
do,
because,
otherwise,
he
could
not
have
planted
his
experiments
the
way
he
did."
Mendel
explicitely
mentioned
his
hypothesis
in
his
Pisum
paper
in
the
part
on
"The
Re-
productive
Cells
of
Hybrids"
on
pages
24
and
25,
which
remained
mostly
neglected.
Those
experiments
were
also
performed
for
demonstration
and
according
to
Mendel
/p.24/
the
goal
of
them
was
to
"throw
light
on
the
composition
of
seed
and
pollen
cells
in
hybrids".
In
the
first
paragraph
of
the
above
mentioned
part
Mendel
defines
his
theory.
To
avoid
the
unexactness
of
interpretation,
Mendel's
original
version
is
given
/pp.24
and
25/.
"Einen
wtchtigen
Anhaltspunkt
bietet
bei
Pisum
der
Umstand,
dass
unter
den
Nachkommen
der
Hybriden
konstante
Formen
auftreten,
und
zwar
in
alien
Kombinirungen
der
verbundenen
Merkmale.
Soweit
die
Erfahrung
reicht,
finden
wir
es
aberall
bestatigt,
dass
konstante
Nachkommen
nur
claim
gebildet
werden
konnen,
wen.n.
die
Keimzellen
und
der
befruchtende
Pollen
gleichartig,
somit
beide
mit
der
Anlage
ausgeriistet
sind,
vollig
gleiche
Individuen
zu
beleben,
wie
das
bei
der
normalen
Befruchtung
der
reinen
Arten
der
Fall
ist.
Wir
mils-
sen
es
daher
als
nothwendig
erachten,
dass
auch
bei
Erzeugung
der
konstanten
Formen
an
der
Hybridpf1anze
vollkommen
gleiche
Faktoren
zusammenwirken.
Da
die
verschiedenen
kon-
stanten
Formen
an
e
iner
Pflanze,
ja
in
einer
Bllithe
derselben
erzeugt
werden,
erscheint
die
Annahme
folgerichtig,
dass
in
den
Fruchtknoten
der
Hybriden
so
vielerlei
/Keimblaschen/
und
in
den
Antheren
so
vielerlei
Pollenzellen
gebildet
werden,
als
kons
tante
Kombina-
tionsformen
m5glich
sind,
und
class
diese
Keim-
und
Pollenzellen
ihrer
inneren
Beschaffen-
heit
nach
den
,einzelnen.
Formen
entsprechen:
,
Mendel
went
on
in
expressing
his
belief
that
/p.24
7
25/
:
"In
der
'That
lasst
sich
auf
theo-
retischem
Weg
zeigen,
x/
dass
these
Annahme
vollstandig
ausreichen
wiirde,
um
die
Ent-
wicklung
der
Hybriden
in
den
einzelnen
Generationen
zu
erklaren,
wenn
man
zugleich
vor-
aussetzen
dilrfte,
dass
die
verschiedenen
Arten
von
Keim-
und
Pollenzellen
an
der
Hybride
durchschnittlich
in
gleicher
Anzahl
gebildet
werden".
In
the
theoretical
logical
proof
of
the
theory
Mendel
could
have
made
full
use
of
the
data
in
Gartner's
book.In
the
next
paragraph
Men-
del
started
with
the
following
words:
"Um
diese
Voraussetzungen
auf
experimentellem
Wege
einer
Priifung
zu
unterziehen,
x
/
wurden
folgende
Versuche
ausgewahlt:
"These
experiments
deal
with
reproductive
cells
of
hybrids.
They
were
brilliantly
planned
and
prepared
by
Men-
del.
In
the
conclusion
of
this
part
Mendel
states
quite
unambiguously
/p.29/
:
"Es
ist
daher
auch
x/
auf
dem
experimentellem
Wege
die
Annahme
gerechtfertigt,
das
s
die
E
r
b
s
en
-
Hybriden
Keim-
und
Pollenzellen
bilden, welche
ihrer
Beschaffen-
heit
nach
in
gleicher Anzahl
alien konstanten
Formen
entsprechen,
welche aus der Kombinirung der
durch Befruchtung vereinigten
Merk-
mal
e
he
rvo
rgehen ".
I
am
stressing
here
Mendel's
word
too
illustrating
that
the
experimental
proof
of
Mendel's
hypothesis
was
for
him
the
second
one.
Mendel
must
have
highly
appreciated
the
experiments
on
reproductive
cells
and
already
in
his
Pisum
paper
recommended
/p.42/
as
follows:
"...
a
repetition
of
at
least
the
more
important
experiments
is
therefore
desirable:
for
instance,
the
one
on
the
composition
of
hybrid
fertilizing
cells".
Similarly
Mendel
recommended
the
performance
of
similar
experi-
x
i
underlined
by
Orel
58
ments
to
Nageli
in
his
second
letter
of
April
18th,
1867.
He
also
used
the
same
approach
in
the
investigation
of
the
illusory
stabile
hybrids
of
Geum,
as
he
mentioned
in
his
third
letter
to
Nageli.
Conclusion
R.
A.
Fisher
/1936/
in
reconstructing
Mendel's
Pisum
experiments
had
to
come
to
the
conclusion
that
Mendel
knew
very
well
what
to
expect.
A
new
attempt
at
a
reconstruction
of
Mendel's
Pisum
data
yielded
some
differences
in
numbers
and
periodical
arrangement
of
the
experiments.
This
fully
confirms
Fisher's
conclusion
that
Mendel
must
have
known
be-
forehand
what
to
expect.
It
is,
however,
improbable
that
the
hybridizing
experiments
pre-
ceded
the
experiments
on
gametic
ratios
as
Fisher
thought.
It
is
most
likely
that
after
con-
cluding
/p.29/
"that
pea
hybrids
form
germinal
and
pollen
cells
that
in
their
composition
correspond
in
equal
numbers
to
all
the
constant
forms
resulting
from
the
combination
of
traits
united
through
fertilization"
Mendel
projected
his
programme
of
hybridizing
peas
differing
in
one
or
more
trait
pairs
to
demonstrate
how
his
idea
worked.
From
the
didactic
point
of
view,
he,
however,
first
described
his
mono-,
di
-and
trihybridizing
experiments
which
he
presumed
to
be
more
easily
comprehensible
to
his
listeners.
A
detailed
explana-
tion
of
his
theory
was
presented
later
in
the
letter,
part
"On
Reproductive
Cells"
and
es-
pecially
in
the
Concluding
Remarks.
*
•m
ook.
R
eferences
Bennett
,
J.H.
1965:
Experiments
in
Plant
Hybridisation
-Gregor
Mendel.
Oliver
&
Boyd,
Edinburgh,
pp.
95.
Correns,
C.
1905:
Gregor
Mendel's
Bridle
an
Carl
Nageli,
1866-1873.
Abhandlungen
der
mathematisch-physikalischen
Klasse
der
kiiniglich
sii.chsischen
Gesellschaft
der
Wissenschaften,
29:189-265.
English
translation
in
C.Stern
and
E.R.Sherwood,
1966
de
Beer,
G.
1965:
Other
Men's
Shoulders.
Annals
of
Science,
20,4:303-322
Dunn,
L.C.
1965:
Mendel,
His
Work
and
its
Place
in
History.
Proceedings
of
the
Ameri-
can
Philosophical
Society,
109,4:189-198
Fisher,
R.A.
1936:
Has
Mendel's
work
been
rediscovered
?
Annals
of
Science,
1:115-137
/
Reprinted
by
Bennet,
1965
and
by
C.
Stern
and
E.R.Sherwood,
1966/
Gartner,
C.
1849:
Versuche
and
Beobachtungen
fiber
die
Bastarderzeugung
im
Pflanzen-
reich.
Stuttgart,
pp.
790
Goss,
J.
1824:
On
the
variation
in
the
colour
of
peas,
occasioned
by
cross
-impregnation.
Transactions
of
the
Horticultural
Society,
London,
5:234-236
Knight,
T.A.
1824:
Some
remarks
on
the
supposed
influence
of
the
pollen,
in
cross
-breed-
ing,
upon
the
colour
of
the
seed
-coats
of
plants,
and
the
qualities
of
their
fruits.
Transactions
of
the
Horticultural
Society,
London,
5:377-380
MENDEL,
G.
1865:
Versuche
fiber
Pflanzen-Hybriden.
Verhandlungen.des
naturforschen-
den
Vereines,
Band
IV.
Abhandlungen,
3-47
Misra,
A.B.
1965:
Luck
and
Pluck
of
Gregor
Mendel.
Mendel
Centenary
Souvenir,
Maharajas
College,
Ernakulam,
p.1-8
59
Seton,
A.
1824:
On
the
variation
in
the
colour
of
peas
from
cross
-impregnation.
Transaction
of
the
Horticultural
Society,
London,
5:236-7
Stern,
C
. ,
E.R.Sherwood,
1966:
The
Origin
of
Genetics
-
A
Mendel
Source
Book.
W.H.
Freeman
and
Co.
,
pp.179
Weiling,
F
.
1970:
Geschichte
des
Textes
der
"Versuche"
sowie
textkritische
Bemerkungen.
In
the
new
edition
of
Mendel's
paper
in
the
serial
Ostwalds
Kiassiker
der
exakten
Wissenschaften.
F
.Vieweg
&
Sohn,
Braunschweig,
pp.110
Wichura,
M.
1865:
Die
Bastardbefruchtung
im
Pflanzenreich,
erllutert
an
den
Bastarden
der
Weiden.
Breslau
Wichura,M.
1853:
tl
ber
kimstlich
erzeugte
Weidenbastarde.
Ber.
Schles.
Ges
.
vaterl.
Kultur,
31:160-164
Zirkle,
C.
1951:
Gregor
Mendel
and
His
Precursors.
Isis,
42:97-104
60