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-
JENS CHRISTIAN CLAUSEN
March ~ 1, 1891-November 22, 1969
BY C. STACY FRENCH
OBSERVERS OF NATURE from primitive man to the most
enlightenec! modern scientists have long speculatecI
on the relative importance of heredity versus environment in
the development of living beings. With regarc! to humans the
subject is so explosive that many fear to learn more. With
regard to plants, however, the issue of development raises no
controversy; experiments can be carried out in peace and
results interpreted rationally. Working as the head of a plant
biology research group at the Carnegie Institution, lens
Christian CIausen successfully cIarifiecI for certain species
and under certain conditions the question of heredity ver-
sus environment so basic to biology.
When still a student in Denmark, fens CIausen became
interested in the genetics of a wide variety of local violet
fount! near his home. A farm boy with sharp powers of ob-
servation, he had a mind that always aspect why. His interest
in living things eventually took him to Copenhagen Univer-
sity for his B.Sc. and M.Sc. degrees and, in 1926, the Ph.D.
in the new field of genetics, and then to an assistant profes-
sorship at the Royal Agricultural College under 0jvincl
Winge—a scholarly botanist whom the young farmer-
student held in consiclerable awe.
In the 1920s, while CIausen was making his name with his
75
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BIOGRAPHICAL MEMOIRS
studies of Danish vegetation, Harvey Monroe Hall, professor
of botany at the University of California, Berkeley, and a re-
search associate of the Carnegie Institution, began trans-
planting native plants into contrasting environments. Sup-
ported by the institution, Hall and two student botanists,
William M. Hiesey ant! Davis! D. Keck, concentrated scat-
terecl transplants into three gardens with very different en-
vironments: one near sea level at Stanford University, one at
an elevation of 4,500 feet at Mather on the western edge of
Ypsemite National Park, and one at 10,000 feet at Timberline
in the High Sierra of Yosemite's far eastern edge. In 1932,
Hall invited CIausen to join his group as a geneticist. But a
few months after CIausen's arrival, Hall cried, leaving CIausen
to take over as the project's director.
lens CIausen's vigor and enthusiasm enabled him to spend
long hours in the field and made him a natural leader and
clelightfu! colleague. A devoted Christian, Jens's faith rein-
forcec! a naturally strong character anc! joy in life, never lim-
iting his independence of thought. He introclucec! many a
famous botanist to the California vegetation of the mountain
stations, and many hacT the good fortune, after a strenuous
day of fieldwork, to enjoy his warm hospitality at the Mather
"Hog Ranch" cabin.
In 1959, at the request of one of his stuclents, lens wrote
a brief autobiography, which written in his own words-
fortunately preserves for us something of his spirit:
CONFESSIONS AND OPINIONS OF AN
ECOLOGIST OF SORTS
Personal Background
Unfortunately, ~ must confess to being born in ~ 89 ~ in
the latter part of the nineteenth century. After a younger
brother cried when he was five and ~ ten years of age, ~ be-
came, essentially, an only child.
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JENS CHRISTIAN CLAUSEN
77
~ cannot claim much formal schooling because ~ went
through only two grades of a four-gracle, every-other-day
country grammar school in Denmark, attending the two up-
per gracles of this school between the ages of eight and thir-
teen. The principal of the school, who was also the teacher
of the two upper classes, had adviser! my father to spare me
from attending the beginner's classes by not starting me in
school until ~ was past eight. He remained a personal friend
of mine as long as he livecI, but ~ must confess that ~ put little
effort into the class work. Insteac! ~ clicl considerable extra-
curricular reading.
The grade school was followed by one year in a private,
local secondary school, where ~ was introducer! to the fun-
ciamentals of English, German, worm history, physical and
natural sciences, anct mathematics. At the age of fourteen ~
left school entirely and took up the farming of my parents'
fifteen-acre place. My father tract been a house-builcler clur-
ing my early boyhood, and as ~ took over the daily running
of the family farm, he resumed his primary interest. Unlike
him, ~ hac! no inclination toward the building trade but was
highly interested in farming. As a consequence, ~ never at-
tencled formal high school (or gymnasium as it was called in
Denmark), but at the age of twenty-two presented myself for
the entrance examination to Copenhagen University an af-
fair lasting a full month and was admitted. Half a year later
had my B.Sc. degree at the University.
As far as my early education, ~ was largely autodidactic. ~
Earned to read at the age of four using the daily newspaper
as a primer and asking my father the meaning of the words.
Curiosity was a driving force, and my father, who himself
hacl been a quick learner, was a sensible person. My mother
had never gone to school but learned at home. Before ~ nor-
mally wouIct have started to school, ~ had learned reacting,
writing, and basic arithmetic. These skills opened the worIct
of books to me, anc! being brought up on a farm ~ also be-
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BIOGRAPHICAL MEMOIRS
came familiar with all kinds of living things ancT with farm
practices. At various times during the early years one Earned
the principles of physics ant! chemistry from everyday ex-
periments and had fun constructing primitive microscopes
and telescopes.
My first introduction to botany was given me at the age
of nine by an uncle who owned my mother's 5-acre birthplace
in a botanically interesting part of the country, sculptured by
high moraines ant] watercourses. My uncle was a farm la-
borer on a neighboring larger farm, but he was highly intel-
ligent, interested in botany, anc! had by himself learned to
recognize most of the Danish wile! plants. T spent short sum-
mer vacations there, anct on weekends he took me along on
hikes over hill anc! clale and through forests. These trips
opened a new world to me.
During my early teens, ~ borrowed from the county li-
brary Eugenius Warming's recently published book, Plante-
samfund, the Danish forerunner of his later, Ecology of Plants,
and considerably more inspired than its English successor. ~
became cleeply interested in this subject, anc! during my high
school years ~ made a cletailecl study of the botanical com-
munities within a 2,000-acre moor area near my home anct
wrote a kind of term paper on the subject as part of my
botanical training.
~ likewise stucliec! geology during my teens on small pri-
vate expeditions around} the country anct on a trip to the
famous Kinnekulle region in central Sweden, which con-
tained a complete succession of the Cambrian and Silurian
deposits. ~ returned from such expeditions with considerable
paleontological and botanical loot. My home was also near
primitive sites of miclclle stone age kitchen mittens, and near
remnants of a neolithic lake-c~weller's community where
stone axes of great artistic beauty had been manufactured
for trade some 4,000 years ago. The hills were stuclded with
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JENS CHRISTIAN CLAUSEN
79
burial sites from bronze and early iron age, uniting the past
with the present.
News of the rediscovery of Menclelism drifter! through
the local newspapers, and in high school ~ also bought the
sixth edition (1906) of Darwin's, The Origin of Species, in En-
glish. Receiving some private tutoring from Mr. Thorgiles,
an unusual teacher who had become headmaster of the sec-
onciary school ~ once attended, ~ was now able to expand on
my previous introduction to the sciences, mathematics, and
the history of the civilizations of the worIcI. Mr. Thorgiles,
more than anyone else, was responsible for introducing me
~o me sc-len~lnc mernoct. A new grasp of foreign languages
also opener! German and English literature to me.
Therefore, although ~ clict not attend formal high school
T ~ 1_ C_ ~ ~ ~
. ~ ~ A
_ _ ~ ~ 7
1 At oL'aL'ly clan Belter training, going on my own, with a little
guidance here and there. Life during those later teens was
interesting and absorbing, as I managed a small dairy farm,
pursued liberal stuclies of many kincis, anc! was church or-
ganist ant! church school teacher on the side.
· .
My original plan had been to go to the Royal Agricultural
College in Copenhagen as a preparation for a farming pro-
fession. From ~ 9 ~ 0, however, at the age of about nineteen, ~
was also a part-time teacher at the secondary school ~ had
attended a few years earlier, teaching primarily science. This
experience was absorbing, and ~ deciclec! to change plans and
attend the university instead. Starting at Copenhagen Uni-
versity in 1913 at the age of twenty-two, ~ majored in botany
and minored in physics, chemistry, geology, geography, and
zoology. In 1920, at the age of thirty, ~ received my master's
degree in natural history and geography. During my student
clays, ~ continue<] to teach in the school but gradually tapered
off on farming. ~ commuted the 30 miles to Copenhagen
certain (lays of the week for the mandatory laboratory
courses and some lectures. Two years ~ 9 ~ 6 to ~ 9 ~ ~—were
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BIOGRAPHICAL MEMOIRS
spent in military service during World War I. At that time,
stationed only ~ miles from Copenhagen, I commuted by
bicycle.
The University of Copenhagen was a true university
rather than a school. It ctid not have residence requirements
ant! one more or less developed one's own plans for study in
consultation with the professors. There were excellent op-
portunities for discussions with professors and with other
students. Chresten Raunkiaer was my major professor in bot-
any, P. Boysen Jensen in plant physiology, and Wilhelm Jo-
hannsen in plant physiology and genetics. I knew Eugenius
Warming, who at that time was retiree! but still highly inter-
ested in the young students. August Krogh was my professor
of animal physiology. ~ started physics uncler Niels Bohr, fol-
lowecl by H. M. Hansen, chemistry under Einar Biilmann
and Chr. Winther, and geography under H. P. Steensby.
Intellectually, it was a highly stimulating environment. We
were a small group of graduate students in biology who met
for discussions, developing foundations for new approaches
to systematics and ecology, sparked by the young science of
genetics. In 1917 Winge defended his cloctoral thesis on the
significance of the numbers of chromosomes in plants, in
which he proposed the polyploidy theory.
When ~ had my first interview with Wilhelm ~ohannsen
in 1913, ~ mentioned that, for my master's clegree, T wanted
to choose a specialty in genetics, and that ~ was interested in
combining the genetic with the ecological approach to the
v A,
study of systematics. Johannsen had no use for ecology and
was rather amuser! at the suggestion. Genetics was still new
at the time, ant! although Johannsen was one of its pioneers,
nobody had ever before specializect in genetics. It was finally
arranged that ~ shouIcl have a specialty both in systematics
and genetics. At Raunkiaer's suggestion ~ chose the violaceae
because they were supposed to contain many natural hybrids.
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JENS CHRISTIAN CLAUSEN
81
Just at the time when Winge developed the polyploidy
theories, ~ found that Viola tricolor had thirteen and ~ arvensis
(a close relative) seventeen pairs of chromosomes not a
polyploid situation. Moreover the two species hybridized at
their points of contact in the wild, and the hybrids were mod-
erately fertile. It so happened that spontaneous hybrid col-
onies of these two species of violet were located a short dis-
tance from the headquarters of the artillery company to
which ~ was assigned, and T set up my microscope on the
office desk of the company command. This was undoubtedly
one of the queerest cannons in artillery history!
After the war ~ toured Denmark studying the wild pop-
ulations of these two Viola species. ~ found prostrate, peren-
nial races of Viola tricolor on exposed maritime sand dunes
and annual, erect races inland—although often in close prox-
imity to the maritime ones. Seedlings of the two kinds re-
tained their identities even when grown remote from the
coast. Viola arvensis was found to be associated with calcareous
soils, tricolor with sandy soils. On neutral to faintly acid soils
in the contact zones could be found swarms of interspecific
hybrids, having intermecliate, irregular chromosome num-
bers. Such spontaneous hybrids of various generations seg-
regated similarly to the artificial hybrids. ~ presented these
findings in two papers published in 192 ~ and 1922 in Botanisk
Tidssbrift. They constitute one of the early approaches to ex-
perimental taxonomy, to studies on natural populations, and
to the subject of gene introgression. These studies showed
that the characters of the two species recombined at their
points of contact, and that genes apparently could migrate
some distance from the point of contact.
Remarkably enough, Gote Turesson's first papers on eco-
types appeared in 1922, and we discovered that, unknown to
each other, we had been working on the same subject of races
of species adjusted to ecologically distinct environments at
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BIOGRAPHICAL MEMOIRS
sister universities only 30 miles apart, though in different
countries. From that time on, there was fairly close liaison
between Copenhagen and Luncl across the souncl.
At the Royal Agricu1ttura1t College, Copenhagen, 1921-1931
After my master's degree, ~ started preparing for my
teacher's credentials, although T tract already taught for ten
years. Three months later, however, in April 1921, the first
genetics department in Denmark was established at the Royal
Agricultural College. 0jvincl Winge became professor, and ~
was offered the assistantship (corresponding to the rank of
assistant professor). As a result ~ did not complete my teach-
er's creclentials but lanclect unexpectedly at the college ~ orig-
inally had aimed for.
The field of the new department was to be basic research
in genetics and not plant breeding a far-sighted arrange-
ment in an agricultural college. During the following ten
years, the genie compositions of many kinds of plants and of
the tropical freshwater fish, Lebistes reticulates, were analyzed;
the existence of sex chromosomes in several dioecious plant
species was ctiscoverecl; it was found that experimentally in-
ducec! cancers of sugar beets ant! mice had abnormal chro-
mosome numbers. We also studied interspecific hybric! prog-
enies of several groups of plants of the genera Melandrium,
Geum, Tragopogon, Erophila, and Hypericum. The papers relat-
ing these results are in Winge's name and much has never
been published, but it was an excellent experience to work
with so many different kinds of organisms.
On my own time, during evenings and vacations, ~ con-
tinued the investigations of the violet species of the Melanium
section. These experiments resulted in a series of papers that
were publishect in Hereditas between 1923 and 193 I, and two
papers on chromosome numbers anct relationships of species
published in Annals of Botany between 1927 and 1929. Mrs.
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JENS CHRISTIAN CLAUSEN
83
CIausen, although herself not a trained biologist, was a clect-
icatec! and skillful helper in the clelicate anct time-consuming
work of crossing, pollinating, and classifying the large F2
progenies, and of fixing and embeclding the buds for cyto-
logical investigations.
My doctoral thesis, "Genetical ant! Cytological Investiga-
tions on Viola tricolor L. and ~ arvensis Murr.," was published
in Hereditas in 1926. As far as ~ know, this is the first clem-
onstration of the fact that taxonomic characters clistinguish-
ing species are controlled by genes that can be analyzed. In
Denmark, as in other Scandinavian countries, the cloctorate
is based on advancecl research, the investigations are con-
ductect after one has ceased being a student at the university,
and there are no faculty advisors. The doctorate carries with
it the right to lecture at the university on subjects of one's
own choosing ant] to conduct courses there.
In 1927, ~ was granted a Rockefeller fellowship for one
year at the University of California at Berkeley. In 1929, to-
gether with E. B. Babcock, who became a lifelong, close
friend, ~ published a paper on chromosome pairing in three
interspecific hybrids of Crepas. But the highly varied and di-
versified California vegetation, which ~ saw in the company
of Babcock anct others, tract an even greater impact on my
ecological thinking. In ~ 93 I, after my return to Copenhagen,
~ published a paper on chromosome pairing in C. H. Osten-
field's interspecific Polemonium hybrids.
With the Carnegie Institution of Washington at Stanforcl, 1931
H. M. Hall pioneered! the transplant investigations in the
Sierra Nevada beginning about 1921, and in 1923 cooper-
ated with Babcock on a combiner! genetic-taxonomic inves-
tigation on the hayfielcl tarweecls, the Euhemizonia section of
the genus Hemizonia of the Madiinae. Hall wrote me aIreacly
in 1922 after my first two papers had been published that he
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BIOGRAPHICAL MEMOIRS
was interested in conducting similar studies in California on
plant relationships. We followed each other's work during the
years ant! met both in California in 1927, ant! in Denmark in
1928. In 1930 ~ was unexpectedly offered a position as cy-
tologist (later biologist) in his new program on experimental
taxonomy, after the department of plant biology of the Car-
negie Institution was established at Stanford in actdition to
the earlier stations in the Sierra Nevada. ~ accepted this offer
in 1931 ant! arrived at Stanford in late October.
Tragically, Hall cliecl four months later in Washington,
D.C. a great loss. ~ fount! myself unexpectedly chosen to
take his place. It was fortunate for the future program that
David D. Keck and William M. Hiesey, who had assisted Hall
and knew the background of the plants were able to remain
as part of the staff. Now began an interesting time of coop-
eration between men of quite different backgrounds and
leanings, representing cytogenetics, ecology, taxonomy, and
physiology.
Ecotype and Varied Environment Studies
Hall's transplant investigations, using plants of many gen-
era and families that were cloned and grown in highly con-
trasting environments had been started to check on claims by
Gaston Bonnier ant! F. E. Clements that lowland plants
changed into alpines upon being transplanted, and vice
versa. In analyzing the results of experiments under careful
and constant control (publishecl in 1940), it became obvious
that no such change takes place, although the transplanted
ramets are mollified in their new environment.
It was more significant, however, that species widely dis-
tributect in western North America contain a fairly large
number of physiologically distinct ecotypes, more so than
Turesson observed in his extensive investigations in northern
Europe. The most intensive sampling of natural populations
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JENS CHRISTIAN CLAUSEN
CHRONOLOGY
97
1891 Born March 11 in Eskilstrup, Denmark, 30 miles
from Copenhagen, to Christen Agustinus Clausen
and Christine Christensen
1905 - 1915 Farmer
1913 Entered Copenhagen University
1910-1916 Teacher in Danish secondary schools
1916 -1918 Artillery Corps, Danish Army
1918-1920 Teacher in Danish secondary schools
1921 Married Anna Hansen (died Palo Alto, California,
August 24, 1956)
1921 - 1931 Research Assistant, Department of Genetics, Royal
Agricultural and Veterinary College, Copenhagen
1926 Ph.D., Copenhagen University
1927 - 1928 Research Fellow, International Education Board at
the University of California, Berkeley
1931 - 1956 Staff, Department of Plant Biology, Carnegie Insti-
tution of Washington, Stanford, California
1936 Lecturer, University of Copenhagen
1943 Naturalized U.S. citizen
1950 Messenger Lectures, Cornell University
1950-1961 Trustee, Berkeley Baptist Divinity School
1951 Professor by Courtesy, Stanford University
1953 Lecturer in Brazilian universities
1956 Retired from Carnegie Institution of Washington
~ {ens preferred the word "pensioned" and kept on
working all his life.)
1962 Lecturer, Vanderbilt University
1963 Lecturer, University of Chicago and Washington
State University
1963-1964 Visiting Professor of Genetics, University of Califor-
nia, Davis
1966 Attended 11th Pacific Science Congress in Tokyo
1969 Died in Palo Alto, California, November 22
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BIOGRAPHICAL MEMOIRS
SELECTED BIBLIOGRAPHY
1921
Studies on the collective species Viola tricolor L. Preliminary notes.
Bot. Tidsskr., 37:205 - 21.
1922
Studies on the collective species Viola tricolor L. II. Bot. Tidsskr.,
37:363-416.
1923
The variation of the wild pansy. Nat. Verden (Copenhagen), 218-
36.
1924
Increase of chromosome numbers in Viola experimentally induced
by crossing. Hereditas, 5:29-32.
1926
Genetical and Cytological Investigations on Viola tricolor L. and ~ ar-
vens~s Murr. Dissertation, University of Copenhagen, III-IV:
1-156. (Also in: Hereditas, 8: 1-156.)
1927
Non-Mendelian inheritance in Viola. Hereditas, 9:245-56.
Chromosome number and the relationship of species in the genus
Viola. Ann. Bot. (London), 41:677-714.
The origin of cultivated pansies. Dan. Garden J., 3:17-18, 40-41.
The chromosomes as carriers of the hereditary units. Frem, 777-
85.
Has there been an evolution? Frem, 202-208.
How do natural variations originate? Frem, 266-74.
1928
Evolution by hybridization between species. Frem, 332-36, 459-
63.
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JENS CHRISTIAN CLAUSEN
1929
99
Chromosome number and relationship of some North American
species of Viola. Ann. Bot., 43:741-64.
Report of the Eighteenth Scandinavian Naturalist Congress, Copen-
hagen: Exchange between chromatics of homologous chro-
mosomes, pp. 239-45; discussion, pp. 245-46.
1930
Inheritance of variegation and of black flower color in Viola tricolor
L. Hereditas, 13 :342-56.
Male sterility in Viola orphanidis. Hereditas, 14:53-72.
Induction of mutations by radiation, x-ray and radium (I and III).
Nat. Verden (Copenhagen), 240-66, 289-312.
1931
Genetic studies in Polemonium. III. Preliminary account on the cy-
tology of species and specific hybrids. Hereditas, 15:62-66.
Danmarks Viol-Arter. Bot. Tidsskr., 41:317-35.
Viola canina L., a cytologically irregular species. Hereditas, 15:67-
88.
Cytogenetic and taxonomic investigations on Melanium violets.
Hereditas, 15:219-308.
1932
Remarks upon H. G. Bruun's paper on Viola canine L. Hereditas,
17:67-70.
Inheritance and synthesis of Melanium violets. Proc. Sixth Int.
Congr. Genet., 2:346-49.
Principles for a joint attack on evolutionary problems. Proc. Sixth
Int. Congr. Genet., 2:21-23.
With David D. Keck and William M. Heusi. Experimental tax-
onomy: Problems and objectives, methods, Madiinae, Zausch-
neria, Penstemon, Potentilla, miscellaneous materials. Carnegie
Inst. Washington Yearb., 31:201-5.
1933
Cytological evidence for the hybrid origin of Pentstemon neotericus
Keck. Hereditas, 18:65 -76.
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100
BIOGRAPHICAL MEMOIRS
With David D. Keck and William M. Heusi. Experimental taxon-
omy: Madiinae, Zauschneris, Potentilla, Penstemon and Viola.
Transplant experiments. Carnegie Inst. Washington Yearb.,
32: 192-96.
1934
With David D. Keck and William M. Heusi. Experimental taxon-
omy: Madiinae, field and herbarium studies, garden observa-
tions, cytology, genetic studies, transplant studies, Zauschneria.
Carnegie Inst. Washington Yearb., 33:173-77.
1935
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: Transplant studies, herbarium studies, field studies, gar-
den studies, miscellaneous investigations. Carnegie Inst. Wash-
ington Yearb., 34:201-6.
1936
The basis for natural systematic units. 19. Nordiska Skandinaviska
Naturforskarmotet i Helsingfors, 520-23.
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: Principles and problems, the species problem, investiga-
tions on Madiinae, transplant studies, other investigations. Car-
negie Inst. Washington Yearb., 35:208-14.
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: Regional differentiation into ecotypes and ecospecies, the
reaction patterns of ecotypes, other investigations. Carnegie
Inst. Washington Yearb., 34:218-21.
1937
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: Compilation of manuscript, evolutionary patterns of the
Madiinae, Madiinae hybrids, transplant experiments (varied
environment investigations), studies abroad, other investiga-
tions. Carnegie Inst. Washington Yearb., 36:209-14.
1939
With D. D. Keck and W. M. Hiesey. The concept of species based
on experiment. Am. l. Bot., 26: 103-6.
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JENS CHRISTIAN CLAUSEN
101
With David D. Keck and William Hiesey. Experimental taxonomy:
Cytological differentiation within species complexes, causes of
discontinuity in nature, other investigations. Carnegie Inst.
Washington Yearb., 38:123-27.
1940
With D. D. Keck and W. M. Hiesey. Experimental Studies on the Nature
of Species. I. E#ect of Varied Environment on Western North American
Plants. Carnegie Institution of Washington Publication no. 520.
Washington, D.C.
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: The organization of plant groups, Madiinae hybrids, pro-
duction of amphiploids, field studies, cytological studies, selec-
tion experiment, status of present knowledge. Carnegie Inst.
Washington Yearb., 39: 158-63.
1941
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: Criteria for relationship, relationships in the genus Layia,
a possible new species of Layia, synthesis of a pre-existing spe-
cies of Madia, other investigations. Carnegie Inst. Washington
Yearb., 40: 160-70.
1942
With W. M. Hiesey and D. D. Keck. Relations between climate and
intra-specific variation in plants. Am. Nat., 76:5-22.
With David D. Keck, William M. Hiesey, and E. V. Martin. Exper-
imental taxonomy: Hereditary composition of climatic races,
physiological studies, investigations of the Madiinae, studies at
the transplant stations. Carnegie Inst. Washington Yearb., 41:
126-34.
1943
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: The biosystematic units, evolutionary sequences, success
or failure of amphiploids, investigations on range and forage
grasses, other studies, guest investigator. Carnegie Inst. Wash-
ington Yearb., 42:91-100.
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102
BIOGRAPHICAL MEMOIRS
1944
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: The depletion of the western range, breeding of range
grasses, taxonomy and distribution of Poa, biological character-
istics of Poa and breeding technique, cytology of Poa, hybridi-
zation of Poa, physiology of climatic races of Achillea, other in-
vestigations. Carnegie Inst. Washington Yearb., 43:69-81.
1945
With D. D. Keck and W. M. Hiesey. Experimental Studies on the Nature
of Species. II. Plant Evolution Through Amphiploidy and Autoploidy,
with Examples from the Madiinae. Carnegie Institution of Wash-
ington Publication no. 564. Washington, D.C.
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: Breeding stock, Poa hybrids, transplant experiments, cy-
tology of range grasses, Achillea studies, future investigations,
guest investigators. Carnegie Inst. Washington Yearb., 44:71-
83.
1946
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: Climatic races of Achillea, Poa investigations, transplant
stations. Carnegie Inst. Washington Yearb., 45 :111-20.
1947
With D. D. Keck and W. M. Hiesey. Heredity of geographically and
ecologically isolated races. Am. Nat., 81 :1 14-33.
With D. D. Keck and W. M. Hiesey. Plant relationship as deter-
mined by experiment. In: Exhibitions Representing Results of Re-
search Scholars, pp. 18-23. Washington, D.C.: Carnegie Institu-
tion of Washington.
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: The physiologic and genetic bases of climatic races; new
hybrid poas for different environments; responses of the Poa
hybrids to different climates; partial apomyxis: an evolutionary
labyrinth; use of the station facilities. Carnegie Inst. Washing-
ton Yearb., 46:95-104.
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JENS C HRI STIAN C LAUSEN
1948
103
With D. D. Keck and W. M. Hiesey. Experimental Studies on the Nature
of Species. III. Environmental Responses of Climatic Races of Achillea.
Carnegie Institution of Washington Publication no. 581. Wash-
ington, D.C.
With David D. Keck and William M. Hiesey. Experimental taxon-
omy: The range-grass program, climatic races of Potentilla glan-
dulosa, genetic analysis of the climatic races, selection experi-
ment, exploratory crossings. Carnegie Inst. Washington Yearb.,
47: 105-10.
1949
Genetics of climatic races of Potentilla glandulosa. (Presented at the
Eighth International Congress of Genetics.) Hereditas, Suppl.
vol.: 162-72.
Evolution in Crepes. Evolution, 3: 185-88.
With David D. Keck, William M. Hiesey, and Paul Grun. Experi-
mental taxonomy: Personnel and guest investigators, Potentilla
gland?llosa, Poa investigations, California plant communities.
Carnegie Inst. Washington Yearb., 48 :95-103.
1950
Leonas Lancelot Burlingame. Rec. Genet. Soc. Am., 19:27-29.
With David D. Keck, William M. Hiesey, and Paul Grun. Experi-
mental taxonomy: Growth of contrasting climatic races un-
der varied temperatures, Poa investigations, Achillea hybrids,
Mimulus studies, cytotaxonomy of the sagebrush, Dodecatheon,
Phaseolus, Armenia. Carnegie Inst. Washington Yearb., 49:
101-1 1.
1951
Stages in the Evolution of Plant Species. Ithaca: Cornell Univ. Press.
Reprinted: New York: Hafner Press (1962~.
With William M. Hiesey, David D. Keck, Paul Grun, Axel Nygren,
and Malcolm Nobs. Climatic tolerances of Poa species and hy-
brids. Carnegie Inst. Washington Yearb., 50:105-8.
With Paul Grun, Axel Nygren, and Malcolm Nobs. Genetics and
evolution of Poa. Carnegie Inst. Washington Yearb., 50:109-11.
OCR for page 104
04
BIOGRAPHICAL MEMOIRS
With William M. Hiesey and Malcolm Nobs. Genetics of climatic
races and species in Achillea. Carnegie Inst. Washington Yearb.,
50:115-17.
1952
With William M. Hiesey, Paul Grun, and Malcolm A. Nobs. Exper-
imental taxonomy: Survey of the range grass program, new Poa
hybrids. Carnegie Inst. Washington Yearb., 51:107-17.
1953
With William M. Hiesey and Malcolm A. Nobs. Experimental tax-
onomy: The Poa program. Carnegie Inst. Washington Yearb.,
52: 169-73.
With William M. Hiesey and Malcolm A. Nobs. Genetic studies on
ecological races. Carnegie Inst. Washington Yearb., 52:174-76.
1954
Partial apomixis as an equilibrium system in evolution. (Presented
at the Ninth International Congress of Genetics, Bellagio, Italy,
1952.) Caryologia (Suppl. vol.), 6:469-79.
The ecological race as a variable biotype compound in dynamic
balance with its environment. In: Proceedings, Symposium on Ge-
netics of Population Structure, pp. 104-13. International Union of
Biological Sciences Series B. no. 15. Secretariat-General de
['Union Internationale des Sciences Bioligiques.
With William M. Hiesey and Malcolm A. Nobs. Experimental tax-
onomy: The Poa program. Carnegie Inst. Washington Yearb.,
53: 150-56.
With Edward L. Triplett. Chromosome numbers of hybrid Poa
lines. Carnegie Inst. Washington Yearb., 53:156-57.
Evolutionary differentiation at tropical latitudes. Carnegie Inst.
Washington Yearb., 53: 162-64.
1955
With William M. Hiesey and Malcolm A. Nobs. Experimental tax-
onomy: Poa investigations. Carnegie Inst. Washington Yearb.,
54: 170-175. Diploid, tetrapoloid and hexaploid hybrids of
Achillea, Chromosome 182-183.
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JENS CHRISTIAN CLAUSEN
105
With Lois M. Cox. Numabers of hybrid Poa lines. Carnegie Insti-
tute Washington Yearb., 54: 175-77.
1956
With William M. Hiesey and Malcolm A. Nobs. Experimental tax-
onomy: Studies in Poa, plantings of Achillea and Mimulus. Car-
negie Inst. Washington Yearb., 55:236-39.
1957
With William M. Hiesey and Malcolm A. Nobs. Contrasting toler-
ance ranges of apomictic species and hybrids of Poa. Carnegie
Inst. Washington Yearb., 56:293-95.
1958
With W. M. Hiesey. Phenotypic expression of genotypes in con-
trasting environments. In: Scottish Plant Breeding Station Report,
pp. 41-51.
The function and evolution of ecotypes, ecospecies, and other nat-
ural entities. Uppsala Univ. Arsskr., 6:139-43. Also in: System-
atics of Today, Uppsala, Lundequistska Bokhandeln.
With William M. Hiesey and Malcolm A. Nobs. Poa investigations.
Carnegie Inst. Washington Yearb., 57:272-78.
With W. M. Hiesey. Experimental Studies on the Nature of Species.
IV Genetic Structure of Ecological Races. Carnegie Institution of
Washington Publication no. 615. Washington, D.C.
1959
Gene systems regulating characters of ecological races and subspe-
cies. In: Proceedings of the Tenth International Congress of Genetics,
vol. 1, pp. 434-43.
With William M. Hiesey and Malcolm A. Nobs. Evolutionary pro-
cesses in apomictic species of Poa. Carnegie Inst. Washington
Yearb., 58:358-60.
1960
A simple method for sampling of natural populations. In: Scottish
Plant Breeding Station Report, pp. 69-75.
With W. M. Hiesey. The balance between coherence and variation
in evolution. Proc. Natl. Acad. Sci. USA, 46:494-506.
OCR for page 106
106
BIOGRAPHICAL MEMOIRS
With Malcolm A. Nobs and William M. Hiesey. Interlatitudinal se-
lection experiments in Poa. Carnegie Inst. Washington Yearb.,
59:322-24.
1961
Introgression facilitated by apomixis in polyploid Poa. Euphytica,
10:87-94.
With P. I. Watson. Phenotypic responses to contrasting environ-
ments in the genus Poa. In: Scottish Plant Breeding Station Report,
pp. 64-78.
With Malcolm A. Nobs and William M. Hiesey. Studies in Poa. Car-
negie Inst. Washington Yearb., 60:384.
1962
With Malcolm A. Nobs, William M. Hiesey, and Frank Nicholson.
Transplant station activities. Carnegie Inst. Washington Yearb.,
61:312-13.
With William M. Hiesey and Malcolm A. Nobs. Studies in Poa hy-
bridization. Carnegie Inst. Washington Yearb., 61 :325-33.
With R. B. Channell. The North American field pansy, Viola rafin-
esauii. Carnegie Inst. Washington Yearb., 61:333-34.
1963
Tree line and germ plasm- a study in evolutionary limitations.
Proc. Natl. Acad. Sci. USA, 50:860-68.
Studies on the distribution of tree species. Carnegie Inst. Washing-
ton Yearb., 62:394-98.
Cytotaxonomy and distributional ecology of western North Amer-
ican violets. Carnegie Inst. Washington Yearb., 62:398-99.
1964
With R. B. Channell and Uzi Nur. Viola rafinesquii, the only Melan-
ium violet native to North America. Rhodora, 66:32-46.
Cytotaxonomy and distributional ecology of western North Amer-
ican violets. Madrono, 17: 173-97.
New combinations in western North American violets. Madrono,
17:295.
Synthesis. In: Genetics Today: Proceedings of the Eleventh International
Congress of Genetics, vol. 2, pp. 447-49.
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JENS CHRISTIAN CLAUSEN
107
1965
Prof. 0jvind Winge. 19. Maj 1886-5. April 1964. Saertryk af Na-
turhistorisk Tidende, 28-29:60-66.
Population studies of alpine and subalpine races of conifers and
willows in the California High Sierra Nevada. Evolution,
19:56-68.
Microclimatic and vegetational contrasts within a sub-alpine valley.
Proc. Natl. Acad. Sci. USA, 53: 1315 -19.
Vegetational and climatic contrasts within the Harvey Monroe Hall
natural area. Carnegie Inst. Washington Yearb., 64:431-35.
1966
Stability of genetic characters in Tragopogon species through 200
years. Trans. Proc. Bot. Soc. Edinburgh, 40:148-58
. . . .
i,
Stored Developments In the cytogenet~cs ot lragopon. Carnegie
Inst. Washington Yearb., 65:471-73.
1967
Biosystematic consequences of ecotypic and chromosomal differ-
entiation. Taxon, 16:271-79.
Clusters of tree species on both sides of the Pacific. Carnegie Inst.
Washington Yearb., 66:234-42.
1969
Vegetation of the Harvey Monroe Hall natural area. Carnegie Inst.
Washington Yearb., 68 :643-44.
1970
Genecology and breeding. In: Estratto da Eurarpia, Fifth Congress
of the European Association for Research on Plant Breeding,
Milan, 1968, pp. 405-24.
The Harvey Monroe Hall Natural Area. Carnegie Institution of Wash-
ington D.P.B. Publication no. 459. Washington, D.C.
Representative terms from entire chapter:
christian clausen
