The Journal of Heredity 78:208-210. 1987.
Tschermak: a non-discoverer
of Mendelism
II. A critique
Floyd V. Monaghan and Alain F. Corcos
In the following discussion those traits that pass
into hybrid association entirely or almost entirely
unchanged, thus themselves representing traits of
the hybrid are termed dominating, and those that
become latent in the association, recessive.
Tschermak wrote as follows about his hybrid
peas of the F2 generation':
IN AN EARLIER PAPER 4 we examined some of
the historical evidence relating to Tschermak's
claim to be an independent rediscoverer of
Mendelism. In that paper we concluded that he
was not. Tschermak wrote two papers in 1900
upon which his claim to have rediscovered the
principles of Mendelism was based. One of
these is the relatively short one that appeared in
the Berichte der Deutsche Botanischen Gesselschaft9. The other, far longer and more complete appeared in the Zeitschrift fur das Landwirtschaftliche Versuchswesen in Oesterreich*0. Because this last article was not
available to us, we depended on the portions
translated by Roberts in his book, Plant Hybridization Before Mendel7 and also in Olby's
book, Origin of Mendelism6. After examination
of this evidence our conclusion expressed above
is well supported. In our view, which is shared
by Stern and Sherwood8, Kotler2, and recently
by Olby6, Tschermak did not understand Mendel's paper when he read it in 1900.
In the following analysis the reader should
keep in mind that by the time Tschermak wrote
his two papers he had already read Mendel.
While correcting the first proofs of his longest
paper he received and read de Vries' paper on
the law of disjunction, and while correcting his
second and final proofs he received and read
Corrcns' paper4. In spite of all this, it is not
evident that he understood the Mendelian concept of dominance. This lack of understanding
permeates his whole approach and virtually destroys his claim to be an independent rediscoverer of Mendelism.
The authors are affiliated with the Department of
Natural Science, Michigan State University, East
Lansing, Ml 48824.
© 1987, American Genetic Association.
208
The Journal of Heredity
Regularly, the one character in question
.. .comes exclusively into expression (dominating character according to Mendel), in contrast
to the recessive character. . .which, however, in
the seeds of the hybrid plants (F2) is accustomed
in part to come to light.
Our first thought on reading this is that he
had read Mendel and did understand him, at
least in part. However, in a later comment on
the same page as the one above, he wrote:
The appearance of the dominating and the recessive character is not a purely exclusive one. In
individual cases, I could, on the contrary, detect
with certainty a simultaneous appearance of
both, that is to say, of transition stages. (Emphasis added.)
This statement, of course, not only contradicts Mendel's clear and explicit statement
about the first generation from the hybrids of
the seven traits used (F2): "Transitional forms
were not observed in any experiment," but it
also contradicts Tschermak's previous statement, a fact that he did not recognize. Hence,
although Tschermak had read Mendel, at least
that part on monohybrids, he did not have a
clear-cut concept of dominance nor did he recognize that the presence of transitional forms
implies lack of dominance.
Reciprocal crosses
A second example, his treatment of reciprocal crosses, further shows the weakness of
Tschermak's concept of dominance9:
In the last four cases of form, and in part, color
differences of the parent sorts.. .each of the parent sorts showed (relatively) more influence upon
the constitution of the crossed product when it
furnished the seed-pod than when it furnished the
pollen.
Tschermak's concept of dominance:
prevalence, relative potency
Let us turn to another quotation that further
indicates Tschermak's concept of dominance
was different from Mendel's10.
In the first case [the F|] there thus exists an
almost absolute dominance, in the second [the
F2] mere superiority [prevalence] (in a certain
relationship).
Downloaded from http://jhered.oxfordjournals.org/ at Penn State University (Paterno Lib) on September 16, 2016
ABSTRACT: An examination of Tschermak's two
papers of 1900 not only reinforces our conclusion cited in our first paper on Tschermak that he
was not a rediscoverer of Mendelism, but also he
did not understand Mendel when he had read it.
His concept of dominance differed from that of
Mendel, and his use of his own concept Is Inconsistent and contradictory. His discussion of his
backcross data Indicated that he had no idea of
the nature of Mendellan ratios. Nowhere did he
develop the Ideas of segregation and Independent assortment.
We should note two points in regard to this
quotation. One is that the statement about the
unequal influence of seed and pollen parents
directly contradicts Mendel, who showed that
Monohybrid crosses
the results of reciprocal fertilizations were the
Tschermak stated that in his opinion the same. The second point is that Mendel limited
main contribution of Mendel was the concept of his statement to the numbers of offspring showdominance. This is an interesting assertion be- ing the character pairs and to no other characcause it shows how little he understood Mendel. teristics. In contrast, Tschermak wrote about
He did not recognize that the "special contribu- the relative amount of influence exerted by the
tion" lies elsewhere; in his empirical laws of the two parents on the "constitution of the crossed
formation and development of hybrids in their product." This is a very general and loose statedescendants, in his quantitative treatment of ment and appears to involve more than the one
inheritance, and his development and use of or two traits, "form and color difference." Interestingly enough, in his shorter paper9,
symbolic notation.
Since Tschermak believed that Mendel's Tschermak stated that for color (green/yellow)
main contribution was the concept of domi- and form (smooth/wrinkled) the results of renance, we should expect him to have a clear-cut ciprocal crosses are the same, "whether the
concept of dominance and recessiveness and seed- or pollen-parent possessed the character
that his views should be essentially the same as (as also Mendel)." Obviously this contradicts
those of Mendel. For reference, here are Men- the quotation above. However, Tschermak did
del's definitions of dominance and recessive- not seem to recognize this fact either here or in
the many other places in which that happens.
ness3:
Tschermak's Difficulty with Mendel's
Concept of Dominance
In the companion paper in the Berichte1 he
refers to the second as showing "mere prepotency (in a fixed proportion)."
From this it appears that for Tschermak
prevalence of appearance of a particular characteristic is evidence that it is a dominant characteristic. If the characteristic with the highest
potency takes over completely it will show absolute dominance and the less potent, the recessive, will not be expressed at all. If the two
characters are equally potent both will appear
in equal numbers and the form will be transitional. In this kind of system dominance of a
character is measured by relative numbers and
is not a constant property of that character but
varies over a wide range.
It is interesting to note that as late as 1925,
Tschermak was still confusing the Mendelian 1
idea of dominance with the old idea of prevalence. In a letter to Roberts7 he wrote:
In this I was struck especially by the different
value of the characters of the individual races
with respect to their structure, cotyledon color
and form (see conclusion III of my first paper, in
which I emphasized besides that, instead of 'dominieren' (dominant), one should say rather 'prevalieren' (predominant) at least in certain cases
(see conclusion VIII).
If this was indeed Tschermak's concept of
dominance there is no reason for him to anticipate, on theoretical grounds or otherwise, that
there should be any fixed ratio of dominants to
recessives in the F2. Nor would such a view lead
to the concept of segregation as already employed implicitly by Mendel and established
Notes
'
explicitly by de Vries. With a non-Mendelian
conception of dominance and no evidence that
he had thought about segregation of characters
in gamete formation and the recombination of
characters in fertilization, it is interesting to
note that Tschermak nevertheless presented
data purporting to show a 3:1 ratio of dominant
to recessive forms in the F| of some of his experiments. For an examination of these data see
Roberts7. Tschermak's summary on the relationships shown by his data7 is as follows:
The number of the bearers of the dominating, or
as the case may be, prevailing characters is thus
related to the bearers of the recessive about as
3:1.
It is difficult to say whether he saw the proportion
3-1 as more significant than representing one out
of a range of many possible values for the 'prevalence' of the dominating character in the F2 generation before he read Mendel.
It happens that his data were slightly closer to
3:1 than to 2:1. The choice of 3:1 may well have
been based on the fact that Mendel gave this as
the ratio. Having obtained the same ratio as
Mendel, he could then claim that, in this matter, he had rediscovered the same relationship
as Mendel. However, Tschermak did not understand the true nature of dominance, nor did he
give any reason why such a ratio should be
expected. He did not discuss the idea of segregation that would lead to such a ratio, nor is
there any evidence in his papers that he had any
idea of the character structure of parents, hybrids, and their offspring as Mendel so clearly
did. Given this, it is difficult to regard him as an
independent rediscoverer of Mendelism.
The backcroas data
Another point of difference between Mendel
and Tschermak that weakens still further his
iclaim to be a rediscoverer of Mendelism is his
treatment of his backcrosses. Again we begin by
quoting Tschermak's report of his experiments
with peas9.
1
When [the emasculated hybrid is] fertilized by
the parental type with the recessive character, the
number of bearers of the recessive character are
increased over that of self-fertilization of the hybrid. The influence of the character 'yellow' in
the seeds of the hybrid was, in this case, reduced
by 57 percent while the character 'green' was
reduced by 43.5 percent.
It is obvious that he made an error in the last
sentence of the quotation above. Both the characters yellow and green cannot be reduced in
frequency as he indicated. Examination of the
German text as reproduced in Fundamenta
Genetica9 shows the translation to be correct.
Notes
And indeed the number of yellow to green seeds is
in the proportion 1.2:1, that of the smooth to
wrinkled 1.75:1, in contrast to...the average
numbers for self-pollination yellow:green »
2.8:1, round:wrinkled 3.1 to 1. The influence of
the character 'yellow* in the seeds of the crossbred pollinated with the recessive, green-seeded
parental variety compared with the influence in
the case of self-pollination of the crossbred was
thus depressed in the proportion 2.3 to 1 (about
57%), that of the character 'smooth' in the proportion 1.8:1 (about 43.5%). The latter, so-called
dominating character thus showed a somewhat
higher prevalence and equally a somewhat greater resistance than the so-called character 'yellow.'
It is interesting that although Tschermak had
read Mendel there is no indication that he saw
any relationship between what he had observed
and Mendel's treatment of backcrosses. In fact
there is nothing Mendelian about his treatment
of these experiments. He is still concerned, as he
was in his treatment of reciprocal crosses with
the relative potency or prevalence of the "socalled" characters, noting that the influence of
the "so-called dominating" characters was depressed but not equally and that they differed in
prevalence. He did not relate the relative frequencies of dominants and recessive in the offspring of the backcross to the character structure (genotype) of the hybrids as Mendel did in
much more complicated instances. Even having
read Mendel and de Vries he did not seem to
understand the process of segregation as implied by the 1:1 ratio or its consequences. Lacking this understanding he had no theoretical
reason to see one ratio as better representative
of the underlying process than another. Thus
1.2:1 and 1.75:1 are equally nonsignificant of
the 1:1 ratio. It is the view of Stern and Sherwood8 that this lack of understanding of his
backcross data destroyed his claim to be a rediscoverer of Mendel.
Tschermak's Difficulty with Mendel's
Symbolic Notations
Although it is clear that Tschermak had read
Mendel well enough to note the 3:1 ratio, there
is no doubt in our minds that he did not continue
his examination of Mendel's paper much be-
yond the monohybrid section. If we study Mendel's paper, we can see quite easily that his
treatment of his monohybrid data is readily accessible by anyone familiar with standard
breeding practice. However, at the conclusion
of this section he introduced the use of combination series written in his symbolic notation and
his mathematical treatment of reversion data.
From this point on, he used less verbal description and depended more and more on the use of
his abstract notation to carry the argument. As
pointed out in an earlier paper5, his search for
quantitative laws governing inheritance, his use
of an abstract symbolic notation, and his application of combination theory created formidable problems for his hearers and for subsequent
readers among whom was Tschermak. To reach
Mendel's treatment of backcrosses, Tschermak
would have had to work his way through Mendel's treatment of his dihybrids, trihybrids, and
the opening of the section on the reproductive
cells of the hybrids. In order to do this, he would
have had to master Mendel's methods as noted
above. We find no evidence to indicate that he
had this mastery.
By contrast, Mendel not only predicted what
the results should be for two much more complicated backcrosses, but also performed the necessary crosses and indicated how the confirmation obtained from them affected the assumptions on which he had based his predictions.
Tschermak and Independent Assortment
Tschermak, as we have pointed out, had a
concept of dominance, though it is defective.
We also have pointed out that he had no concept
of segregation. As we shall demonstrate in our
discussion of his two-trait data, he did not have
a concept of independent assortment either. In
these experiments, he reported results that he
interpreted as giving a 9:3:3:1 ratio of phenotypes in the F2. This ratio had been discovered
earlier by Correns and reported by him in his
1900 paper1, which Tschermak had seen while
correcting the second proof of his paper from
which his two-trait data are taken.
Tschermak's "final conclusion" to his paper
is given below as translated by Roberts7.
From this essential approach to average value,
there results, in my judgment, the conclusion,
that the combination of two dominating (or recessive) characters in the one parent form results
in the same relationship in the seed product of the
hybrids, as the characters in question do when
isolated. An alteration of the value, or an increase
of the prevalence, does not thereby enter.
Tschermak concluded that the dominant
characters remain dominant, the recessives remain recessive, and the relationship of each
dominant to its contrasting recessive has remained unchanged when they are combined in
the dihybrid. This seems to imply that the ratio
of "about 3 to 1" still holds for each pair independently. However, he did not comment on the
fact that there are two classes of offspring in the
F2 in which new combinations of characters
occur. Both Mendel and Correns did observe
this. Tschermak did not see that the 9:3:3:1
ratio and the presence of these new phenotypes
implied independent assortment of each pair in
May/June 1987
209
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Even though he had read Mendel, de Vries,
and Correns he did not come down unequivocally on the 3:1 ratio either as the limit approached
by his data or as the general pattern for all
dominant-recessive character pairs.
Given his confusion on the nature of dominance and his continued use of the concepts of
potency and prevalence there was, as we commented above, little or no reason for Tschermak
to expect a 3:1 ratio. We agree with Olby's
following comment6:
Examination of the same sentence in Tschermak's longer paper, however10, showed that the
character green (gruen) was given there as
smooth (glatt). From this it appears that an
error was made when the briefer paper in the
Berichte was prepared.
Leaving the error aside, the above quotation
is a good example of the convoluted character of
Tschermak's thought. He wrote about the percentages of the recessives being increased but
offered an example in which the percentage of
dominants is decreased. Moreover, he gave no
evidence of knowing that the result of a backcross of this type must be in the ratio of 1 to 1.
His use of the terms decrease and increase in
comparing the results of two types of crosses
implies that many intermediate values are possible rather than just two specific ones.
The longer paper as reported in Olby* gives a
fuller statement of the difference between backcross results and those from self-fertilization.
However, there is no evidence of an attempt to
frame generalizations of the data from which
new experiments might be projected. Neither
did Tschermak attempt to explain the results of
other investigators in terms of his results. There
is no evidence of an attempt to discover empirical natural laws relating to the formation of
hybrids and the development of their progeny.
By contrast, Mendel did these things again and
again. Nowhere in Tschermak's papers were
there any attempts to propose a theoretical process or mechanism that could account for his
observed results. And there is no evidence that
he understood those parts of Mendel's paper
concerned with this. For example Tschermak
did not discuss, as Mendel did, the possible
composition of egg and pollen cells and their
relationship to the data. Tschermak's failure of
understanding dominance blocked him from
grasping the concept of segregation, a necessary
step in understanding Mendelism.
It is the failure on the part of Tschermak
together with his evident confusion and his contradictions noted above that are major reasons
why we believe that Tschermak should never
have been included among the independent rediscoverers of Mendelism.
Conclusion
There is no question that Tschermak had, by
1900, accumulated numerical data from his
breeding experiments with peas that could be
interpreted as giving the 3:1 and 9:3:3:1 ratios.
The Journal of Heredity 78:210-212. 1987.
Isozyme variation in
proso millet
Suzanne I. Warwick
ABSTRACT. Proso millet (Panlcum mlllaceum L.),
a cultivated species, exhibits considerable morphological and physiological variation, including
The author is affiliated with the Biosystematics
Research Center, Agriculture Canada, Wm Saunders
Bldg., C.E.F., Ottawa, Ontario, Canada KIA 0C6.
She thanks L. D. Gottlieb, University of California,
for his advice on preliminary electrophoretic studies of
proso millet conducted in his laboratory and L. Black
for assistance in conducting further enzyme assays; H.
Scholz, Museum Berlin-Dahlem for providing seed of
ssp. ruderale; P. Cavers and M. Bough, University of
Western Ontario for their assistance in providing
germplasm collections; P. Catling and S. E. Weaver,
Agriculture Canada, S. C H. Barrett, University of
Toronto and L. D. Gottlieb for offering constructive
criticism of the manuscript
© 1987, American Genetic Association.
210
The Journal of Heredity
References
1. CORRENS, C. G. Mendel's Rcgcl ubcr das Verhalten der Nachkonmenschaft der Rassenbastarde. Berichte der Deutschen Botanischen Ges-
the relatively recent divergence of weedy
strains. Isozyme variation was assessed for
seedlings grown from 110 world-wide accessions of proso millet, Including seed material
from two world seed banks representing cultivated varieties, and weedy strains from North
America and Europe. Variation was detected in
only two (AAT and 6PGD) of the 11 enzyme
systems examined. All plants were monomorphlc for identical alleles for eight loci. Fixed
heterozygous phenotypes were observed at 11
of the 19 enzyme loci examined. Only five multilocus genotypes were evident, these differing by
only one or two alleles from each other. There
was no obvious correlation of isozyme patterns
with seed color type, degree of weedlness, and
geographical origin. All of the populations contained a single genotype and 65 percent of the
collections contained the same genotype. All
North American weedy strains of proso millet
were either one or the other of two genotypes.
All black-seeded weedy strains of the species
from both Europe and North America contained
the most common genotype.
PROSO MILLET (Panicum milaceum L.), a native cereal of the Old World, is grown in North
America mainly for bird seed, although it is
widely cultivated for human consumption else-
2.
3
4.
5.
6.
7.
selschaft 18:158-168. English translation by
Leonie Kellen Piternick in the Birth of Genetics.
Genetics 35: No. 5 part 2 Sept. 1950.
KOTTLER, M. Hugo de Vries and the rediscovery
of Mendel's laws. Ann. Sci. 36517-538. 1979.
MENDEL, G. J Experiments in plant hybridization In The Origins of Genetics. C. Stern and E.
R. Sherwood, Eds. W.H. Freeman, San Francisco 1966.
MONAGHAN, F. and A. CORCOS. Tschermak: A
non-discoverer of Mendelism. I An historical
note J. Hered. 77:468-469. 1986.
and
. Reexamination of the fate of
Mendel's paper. J.Hered.l%\ 16-118. 1987.
OLBY, R. Origins of Mendelism. Seconded University of Chicago Press. 1985.
ROBERTS, H. J. Plant Hybridization before
Mendel. Hafner Publishing Co., New York/London. 1965. (Facsimile of the 1929 edition)
8. STERN, C. and E. SHERWOOD, Eds. The Origins
Downloaded from http://jhered.oxfordjournals.org/ at Penn State University (Paterno Lib) on September 16, 2016
gamete formation followed by random recombination in fertilization. Both Mendel and Correns did understand this. Tschermak also concluded that neither of the dominant characters
experienced any increase in prevalence as a result of their close association in the hybrid.
From this it appears that he was still associating
prevalence with dominance, a confusion we
have commented on earlier.
Tschermak obtained numerical results for
monohybrids F2s that appear to approach the 3
to 1 ratio as a limiting value. And in a like
fashion he obtained numerical results for dihybrid F2s that appear to approach the 9:3:3:1
ratio as a limit. But it is one thing to have
obtained such numerical results and quite another thing to understand why those results
"are as they are and not otherwise." Mendel
had that understanding of his results. We can
find no evidence that Tschermak had such understanding even after reading Mendel, de
Vries, and Correns. Not only did Tschermak
show no evidence of this understanding and often misinterpreted Mendel, but also he often
contradicted both Mendel and himself, seemingly without realizing that he had done so.
of Genetics. W.H. Freeman, San Francisco
1966.
9. TSCHERMAK, E. Uber Kunstliche Kreuzung bei
Pisum salivum. Berichte Deutsche Botanischen
Gesselschaft 18:232-239 1900 Reproduced in
Fundamema Genetica. "The revised edition of
Mendel's classic paper with a collection of 27
original papers during the rediscovery area. Anthropological publications, publishing house of
the Czechoslovak Academy of Sciences, Prague
1965 English translation by Aloha Hannah in the
Birth of Genetics. Genetics 35: No. 5, part 2. Sept.
1950.
10
. Uber Kunstliche Kreuzung bei Pisum salivum. Zeitschrift Land Wirtschaftliche Versuchswesen Oestereich 3.465-555. 1900
where6. Proso millet is an example of a crop
species in which weedy strains have recently
evolved6. The development of weedy strains
from cultivated plant species represents a rather subtle intra-specific evolutionary strategy in
the evolution of weeds and one that will result in
increased difficulties in weed control110.
Weedy populations of proso millet were first
observed in the midwestern United States and
parts of Canada in the early 1970s6. The species
now occurs in three states (Wisconsin, Minnesota, and North Dakota) and in three provinces
in Canada (Ontario, Quebec, and Manitoba)3-6.!
Several different biotypes of the weed exist;
these differ in seed color, degree of openness of
the panicle, seed shattering, seed dormancy,
seedling vigor, and competitive ability3-5".
Only the black-seeded weedy biotype of proso
millet has received taxonomic recognition as P.
spontaneum Lyss. (= P. miliaceum var. ruderale Kitag. = P. ruderale (Kitag.) Lyss.3). Based'
on seed protein analysis, Oestry and Dewet12
considered the black-seeded biotype to be a subspecies of P. miliaceum (ssp. ruderale) rather
than a separate species.
Electrophoretic assays of allozymes have
proven useful in elucidating evolutionary relationships and levels of genetic divergence in
many cultivated groups". The purpose of the
following study was to examine allozyme diver-
Notes