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Basic versus applied research: Julius Sachs (1832–1897) and the
experimental physiology of plants
Ulrich Kutschera*
Institute of Biology; University of Kassel; Kassel, Germany
The German biologist Julius Sachs
was the first to introduce controlled,
accurate, quantitative experimentation
into the botanical sciences, and is
regarded as the founder of modern plant
physiology. His seminal monograph
Experimental-Physiologie der Pflanzen
(Experimental Physiology of Plants) was
published 150 y ago (1865), when Sachs
was employed as a lecturer at the Agricul-
tural Academy in Poppelsdorf/Bonn
(now part of the University). This book
marks the beginning of a new era of basic
and applied plant science. In this contri-
bution, I summarize the achievements of
Sachs and outline his lasting legacy. In
addition, I show that Sachs was one of
the first biologists who integrated bacte-
ria, which he considered to be descend-
ants of fungi, into the botanical sciences
and discussed their interaction with land
plants (degradation of wood etc.). This
“plant-microbe-view” of green organisms
was extended and elaborated by the
laboratory botanist Wilhelm Pfeffer
(1845–1920), so that the term “Sachs-
Pfeffer-Principle of Experimental Plant
Research” appears to be appropriate to
characterize this novel way of performing
scientific studies on green, photoautotro-
phic organisms (embryophytes, algae,
cyanobacteria).
Introduction
The chemist Justus Liebig (1803–
1873) was, together with his older col-
league Carl Sprengel (1787–1859), one of
the pioneers of an applied area of plant-
based research that was known in the 19th
century as “Agriculturchemie” (agricul-
tural chemistry). In his seminal 1840-
book Die Organische Chemie in ihrer
Anwendung auf Agricultur und Physiologie
(Organic Chemistry in its Application to
Agriculture and Physiology),
1
Liebig pro-
posed a novel theory of plant nutrition,
arguing that the chemical elements of
Nitrogen (N), Phosphorus (P) and Potas-
sium (K) are key components to support
vegetative growth and crop production. In
addition, he reported that plants acquire
the elements Carbon (C) and Hydrogen
(H) from the atmosphere, and water
(H
2
O), plus dissolved mineral salts, from
the soil. Unfortunately, Liebig’s conclu-
sions, notably his version of the “theory of
mineral nutrition of plants,” were largely
based on older experiments performed by
other investigators, or of speculative
nature
2
.
However, Liebig’s political agenda to
popularize the image of chemistry and its
use in agriculture was, at least in part,
responsible for the establishment of Ger-
man academic research stations aimed at
increasing crop production during the
Industrial Revolution.
3
In 1861, the 29-year-old Privatdozent
(Lecturer) Dr. Julius Sachs was appointed
as a teacher/researcher to the Landwirt-
schaftliche Akademie zu Poppelsdorf/Bonn
(Agricultural Academy of Poppelsdorf/
Bonn), an Institution that later became
part of the University (Fig. 1). In a short
Curriculum Vitae that he had to submit
to the German government in Berlin,
Sachs summarized his life as follows:
“Ferdinand Gustav Julius Sachs,
Dr. philos., teacher of natural sciences at
the Agricultural College of Poppelsdorf,
born Oct. Two, 1832 in Breslau, evangeli-
cal Christian. Father: Christian Gottlieb
Sachs, Engraver in Breslau, deceased;
Mother: Theresa Sachs, geb. Hofbauer,
Keywords: bacteria, epiphytes, experimen-
tal plant physiology, Julius Sachs, plant
science
*Correspondence to: Ulrich Kutschera; Email:
kut@uni-kassel.de
Submitted: 05/26/2015
Revised: 06/09/2015
Accepted: 06/10/2015
http://dx.doi.org/10.1080/15592324.2015.1062958
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Plant Signaling & Behavior 10:9, e1062958; September 2015; © 2015 Taylor and Francis Group, LLC
PERSPECTIVE
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also deceased in Breslau. Until my 6th
year, I lived in Breslau . . . 1845 I attended
the Gymnasium Elisabethanum and
earned, over the next 5 years, a ‘praemium
pro studio et virtute’. After the death of
my parents (1848) I was, due to lack of
any means, forced to leave the Gymna-
sium, and followed Professor Purkinje,
who moved to Prague. In this city, I
earned my Maturitaets-Examination (high
school diploma) at the Clementinum, was
then, for 3 years, a student of ‘higher phil-
osophy’ at the University of Prague, and
earned, after the successful passing of
the required 4 examinations, my
Ph.D. (1856). One year later, I obtained
the venia legendi for Prague University and
remained in this city as a Dozent (Lec-
turer) of Plant Physiology. 1859 I accepted
a position in Tharandt, where I remained
until the end of 1860. In the following
year (1861), I was a teacher of Physiology
at a school in Chemnitz, but gave up this
position to come to Poppelsdorf.
On March 28, 1861, I was appointed
as Lecturer at the Agricultural Academy at
Poppelsdorf. Salary: 800 Thaler. No other
job; since May 18, 1861 married to
Johanna n!ee Claudius from Prague. No
children, without wealth and debt” (trans-
lated from the German text, ref.4).
During his 6-year-tenure in Poppels-
dorf/Bonn, Sachs published 46 scientific
papers and worked on his most influential
book, the Handbuch der Experimental-
Physiologie der Pflanzen (Experimental
Physiology of Plants)
5
(Fig. 1). This
monograph inaugurated a new branch of
experimental botany
6
that will be detailed
in the next section.
The Multi-Author Handbook that
was Never Finished
In 1857, Julius Sachs (Fig. 2) con-
tacted his colleague Wilhelm Hofmeister
(1824–1877), the discoverer of the
homology of the life cycles in bryophytes,
pteridophytes, and coniferous seed plants.
A few years later (1861), Hofmeister
became the Editor of a Four-Vol.-mono-
graph entitled Handbuch der Physiologi-
schen Botanik (Handbook of Physiological
Botany).
7
Unfortunately, the Handbuch,
as envisioned by the Editor Hofmeister in
1866, was never published as scheduled,
because one of the invited authors, Thilo
Irmisch (1816–1879), did not submit the
text assigned to him.
8
In 1877, after Hofmeister’s death, A.
de Bary (Strassburg) and J. Sachs (Wuerz-
burg) announced, in the preface to Vol.
III, the formal completion of this multi-
author-monograph. The five books (Vols.
I – IV) were arranged by de Bary and
Sachs as follows:
Vol. I: W. Hofmeister (1867/1868)
Die Lehre von der Pflanzenzelle
(Plant Cell Biology) (A)
Allgemeine Morphologie der Gew€
achse
(General Morphology of Plants) (B)
Vol. II: A. de Bary (1866) Morpholo-
gie und Physiologie der Pilze, Flechten
und Myxomyceten
(Morphology and Physiology of
Fungi, Lichens and Myxomycetes)
Vol. III: A. de Bary (1877) Verglei-
chende Anatomie der Vegetationsorgane
der Gef€
asspflanzen
(Comparative Anatomy of the Vege-
tation Organs of Cryptogams)
Vol. IV: J. Sachs (1865) Experimental-
Physiologie der Pflanzen
(Experimental Physiology of Plants)
Vols. I to IV (i.e., 5 separate books)
were published by the Verlag Wil-
helm Engelmann in Leipzig.
This arrangement shows that 1. the
two books of Hofmeister (1867/1868)
were combined and issued as Vol. I; 2. the
Experimental-Physiologie of Sachs (1865),
which was published first, finally became
Vol. IV, and 3. de Bary’s monograph of
1877, with a concluding “Preface” signed
by the author and Sachs on behalf of the
deceased Hofmeister, represented Vol. III
of this multi-author book.
The “Tables of Contents” of the
“Handbook of Physiological Botany”
(Vol. I to IV, 1865–1877)
8
shows that
19th-century botanists studied all plant-
like organisms that were not
Figure 1. The 29-year-old Julius Sachs (1832–1897) (6th from the left) among some of his col-
leagues at the Agricultural Academy in Poppelsdorf/Bonn (i.e., the building in the background). Dur-
ing his 6-year-tenure, Sachs published, in addition to numerous journal articles, his textbook
Experimental Physiology of Plants (1865) (adapted from ref.4).
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unequivocally classified as animals: algae
(inclusive of the blue greens, i.e., cyano-
bacteria), vascular cryptogams, bryo-
phytes, angiosperms, lichens, fungi and
plasmodial slime molds (myxomycetes).
In 1872, the botanist Ferdinand Cohn
(1828–1898) described microorganisms
associated with plant material, and coined
the name “Schizomyceten,” or “Spalt-
Pilze” (Bakterien) for these tiny living
beings.
9
These prokaryotic microbes (that
were discovered and described as
“animalcules” in 1676 by Antonie van
Leeuwenhoek, 1632–1723) were system-
atically investigated by botanists since ca.
1873.
This broad view of “the Plant King-
dom” is in contrast to the more specific
opinion that Sachs (Fig. 2) expressed in
his Experimental-Physiologie. Despite the
fact that he referred, within the context of
protoplasmic streaming, to de Bary’s work
on the myxomycetes, the author largely
focused on crop species, such as maize
(“Turkish wheat”), bread wheat, sun-
flower, buckwheat, cucumber, broad bean
etc. Accordingly, his favorite “green
plants” were all characterized by oxygen-
producing photosynthesis, a process he
had studied over many years (for instance,
light-induced accumulation of starch
grains within the “chlorophyll bodies” of
leaves; release of O
2
-bubbles in irradiated
aquatic plants that were maintained in
CO
2
-enriched water etc.).
A Novel Botanical Research
Agenda
As mentioned above, the key publica-
tion of Sachs, his Experimental-Physiologie
der Pflanzen (Experimental Physiology of
Plants) was Vol. IV of an (unfinished)
multi-author-monograph entitled
“Physiological Botany.” In contrast to the
book of Sachs (1865)
5
(Fig. 1), which is
still popular today, the other parts of
Hofmeister’s series of monographs
remained largely unknown. In his master-
piece, which was highly praised by Francis
Darwin (1848–1925) and other
well-known plant scientists, Sachs (1865)
summarized all areas of plant research
established at that time, and based his gen-
eral conclusions mostly on his own
experimental studies. The author
described, in chapters I to XIII, not only
the effects of light, temperature, electric-
ity, gravity, nutrients and atmospheric
oxygen on physiological processes in
plants, but also summarized the following
topics: transformation of substances,
translocation of organic material, molecu-
lar architecture of starch, and tissue ten-
sion in relation to organ growth. The
book was published in November 1865
and was rapidly sold out. Translations
into French (1868) and Russian (1867)
made this publication well-known
throughout many parts of Europe.
10
Three key features characterize Sachs’
Experimental Physiology that distinguishes
this monograph from all of its predecessors
(for instance, the 2 books of Hermann
Schacht [1814–1864] on the Anatomy and
Physiology of Plants, 1856/1859, wherein
“vegetation forces” etc. are discussed):
6
1. In contrast to Schacht and others,
Sachs (1865) did not mention “vital
forces” etc.; he exclusively explained
living processes in plants with reference
to physical and chemical principles.
2. Sachs (1865) described novel methods
and apparatuses for the experimental
analysis of plant development and
other physiological processes (water
transport, transpiration, root pressure,
germination, respiration, photosynthe-
sis etc.). Moreover, he clearly pointed
out that controlled, defined conditions
(constant temperature etc.) are neces-
sary to obtain reliable, reproducible,
and hence meaningful results (Fig. 3).
This was the major reason why the
German biologist did not accept the
“country-house-studies” of Charles
Darwin and others
11
– Sachs had no
trust in the experimental results
obtained under variable environmental
Figure 2. Julius Sachs (1832–1897), the founder of experimental plant physiology. Relief on the
outside of the lecture hall, Institute of Agricultural Botany, University of Bonn, Germany (Artwork:
A. Reusch) (adapted from ref. 7).
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conditions. In addition to physiologi-
cal phenomena investigated on whole
plants, Sachs also studied intracellular
processes. For instance, in Chapter VII
entitled Molecularstructur he described
and illustrated protoplasmic streaming
in the hair cells of a squash (Cucurbita
pepo L.) plant (Fig. 4). In this context,
Sachs
5
referred to the
“Chlorophyllk€orner” (chloroplasts)
and compared these intracellular rotary
movements with those observed in
plasmodia of the myxomycetes.
3. Contrary to most other botanists of his
time, Sachs
5
made references to agri-
culture and practical applications of
botanical studies. This may be due to
the fact that Julius Sachs established
his independent scientific career at
institutions devoted to applied botany
and agricultural research (Fig. 1),
rather than in classical Botanical Insti-
tutes at Universities.
For instance, Sachs analyzed the associ-
ation of the root with soil particles in crop
plants such as bread wheat (Triticum aesti-
vum L.) (Fig. 5A), and discovered that the
root hairs are largely responsible for the
uptake of water and dissolved mineral salts
(Fig. 5B). Together with Sachs’ well-
known hydroculture-experiments, these
studies established “root biology” as a new
scientific discipline. As summarized by
Hoexterman (1999)
10
and others,
11,12
most conclusions and theoretical concepts
of Sachs concerning plant development,
metabolism and behavior have been con-
firmed by subsequent investigators,
13-16
with few exceptions (for instance, his
“imbibition theory of water transport”).
Since the German botanist studied the
physiology of crop plants with reference
to agriculture, he established a new branch
of the botanical sciences. This practical
aspect of the work of Sachs is discussed in
the next section.
Basic versus Applied Plant
Research
In 1859, when Sachs was still a Lec-
turer at the University of Prague, the 27-
year-old plant physiologist published a
provocative thesis-paper in the journal
Der Chemische Ackersmann (The Chemical
Agriculturist) (Fig. 6). In this theoretical/
philosophical contribution, Sachs
(1859)
17
argued that the science of plant
physiology had been created by a few,
curiosity-driven men (most of whom were
poor), without financial aid from Govern-
ment-supported Institutions. Moreover,
he complained that “while everything in
the world can be purchased; there are still
many people who want to obtain knowl-
edge, the most precious human product,
free of charge” (ref.17).
Based on these premises, Sachs
17
con-
cluded that Agricultural Colleges, devoted
to research dealing with the improvement
of crop productivity, should employ not
only chemists, but also plant physiologists.
Moreover, he suggested that, in addition
Figure 4. Drawing of a hair cell of a flower bud from squash (Cucurbita pepo L.), showing the
phenomenon of protoplasmic streaming. The nucleus is in the center of the cell, and numerous
chloroplasts are visible (adapted from ref.5).
Figure 3. Custom-built apparatuses constructed and used by Julius Sachs during his tenure at the Agricultural Academy in Poppelsdorf/Bonn. Methods
for the quantification of transpiration (A, B), root pressure (C), and the effect of temperature on seed germination (D) (adapted from ref.5).
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to theoretical plant physiology, a second,
applied branch should be established,
which he labeled as “Agricultural Physi-
ology.” According to Sachs, agricultural
physiologists, who focus on crop plants,
should get positions at research stations to
supplement the work of chemists using
“the physiological approach,” i.e., to eluci-
date open questions via “anatomical analy-
ses and experiments” (Sachs 1859).
17
It is obvious that Sachs’ concept of
“agricultural (i.e., applied) plant physi-
ology” was reminiscent to the ideas
expressed in Liebig’s monograph of 1840,
but the younger physiologist proposed a
much more precise concept than the older
chemist.
According to Sachs (1859)
17
, the coop-
eration of plant physiologists and chemists
at Agricultural stations has the aim to
improve and secure crop productivity.
Under the headline “Tasks of the Agricul-
tural physiologist,” he lists the following
topics:
1. Seed germination (density of propa-
gules, temperature, moisture, depth of
the soil etc.).
2. Function of different plant organs dur-
ing development (water- and nutrient
uptake via the root system; leaves as
assimilatory organs; senescence etc.).
3. Fruit development (role of plant nutri-
tion; source and uptake of organic sub-
stances etc.) (ref.17).
Hence, the 27-year-old Julius Sachs
defined plant physiology in 1859 as a
basic and applied branch of the botanical
sciences (Fig. 6). This novel view was
elaborated and extended in his seminal
Handbuch of 1865 (Fig. 1).
Recognition and Neglect of the
Sachsian Research Agenda
Six decades after the publication of the
Handbuch (Fig. 1), the American Society of
Plant Physiologists (ASPP) (re-named in
2001 as the ASP Biologists, ASPB) was
founded (1924), and in January 1926,
Issue 1 of Vol. One of the new Journal
Plant Physiology appeared in print. In the
Foreword, the Editors explained the aims
and scope of their new Periodical as
follows: “With this issue, PLANT PHYSIOL-
OGY takes its place among the American
journals published in the interests of
botanical science. The Editors conceive
their task as one of devoted service to the
whole field of plant physiology;...
Research in plant physiology must pro-
ceed in 2 general directions. It must con-
tinue to spread out into the practical fields
of human service, such as agriculture, hor-
ticulture, agronomy, ecology, pathology,
forestry, climatology, etc.; at the same
time it must constantly delve more deeply
into the problems of developmental
metabolism under the leadership of physi-
ologists well trained in the methods of
biophysics and biochemistry. Exploratory
research, . . . is of the utmost importance
for the practical fields, for it yields us a
broader knowledge of the methods of con-
trol of plant behavior and plant produc-
tion. But exploratory research alone must
lead only to empiricism, to rule of thumb
methods of practice. Such exploratory
research must be followed by an investiga-
tion of the fundamental causes of observed
Figure 5. Drawing of a wheat (Triticum aestivum L.) seedling, with soil particles attached to the roots
(A), and schematic rendering of the soil, penetrated by root hairs (B). Note that in this scheme the
soil is composed of 3 phases: air-bubbles, capillary water and solid particles (adapted from ref.5).
Figure 6. Headline (“How can a closer cooperation of Plant Physiology with Agricultural Chemistry
be achieved?”) and key sentences of an important theoretical contribution of Julius Sachs published
in 1859. The author argued that plant physiology and agricultural chemistry should join forces for
the improvement of crop productivity.
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behavior. ... It is evident therefore that
these 2 lines of investigation, practical and
fundamental, must always go hand in
hand. There can never be a logical separa-
tion of these 2 aspects of our science. Like-
wise, there can never be a logical
separation of the pure physiologists from
the practical physiologists. Our tasks are
one, and we must learn to march together
in their performance. . . . To this end it
invites the support of plant physiologists
of every denomination, ‘fundamentalists
and modernists’, pure physiologists and
applied physiologists. It has no other pur-
pose, and no other desires than to be of
service, and to promote cooperation in the
common tasks of advancing plant physiol-
ogy as a pure and applied botanical scien-
ce” (the Editors, 1926).
18
It is obvious that in this anonymous
Editorial, the vision of Sachs (1859)
17
is
expressed in words that are similar to
those used by the German botanist deca-
des earlier (Fig. 6). Accordingly, the life
and scientific legacy of Julius Sachs was
described in Vol. Four (1929) of the
American journal Plant Physiology,
19
a
clear indication of the enormous interna-
tional reputation of the German biologist.
In November 2014, the Botanical Soci-
ety of America (BSA), established in 1893,
published a Special Issue entitled
“Speaking of Food: Connecting Basic and
Applied Plant Science.” In the Introduc-
tion, Gross et al. (2014)
20
argued that,
since the “Food and Agricultural Organi-
zation of the United Nations predicts that
food production must rise by 70% over
the next 40 y to meet the demands of a
growing population expected to reach 9
billion by the year 2050,” basic plant sci-
ence is of great importance for agriculture.
With reference to the work of the French
chemist and bacteriologist Louis Pasteur
(1822–1895), Gross et al. (2014)
20
distin-
guished between “Pure basic research (N.
Bohr), Use-inspired basic research (L. Pas-
teur), and Pure applied research
(T. Edison).”
However, the second concept, which
has also been called “Pasteur’s quadrant”
(Strokes 1997),
21
is not new – it was pro-
posed for the first time by Sachs (1859)
17
,
and this principle of “use-inspired basic
plant research” is described in detail in his
Experimental-Physiologie der Pflanzen
(Sachs 1865)
5
(Fig. 1).
Louis Pasteur’s work was used by
Strokes
21
and Gross et al.
20
to illustrate
the synthesis of basic and applied plant
research, whereas the important contribu-
tions of Julius Sachs, the founder of mod-
ern plant physiology (Figs. 1, 2), where
ignored. This may, in part, be due to the
fact that Pasteur had studied bacteria,
which were primarily viewed as pathogens
of humans (“germ theory of disease”);
hence, a medicinal aspect was associated
with the research agenda of the French sci-
entist that made his work much better
known than that of the German botanist
Julius Sachs.
Plants, Fungi and Bacteria
In his Experimental-Physiologie der
Pflanzen of 1865, Sachs
5
illustrated all
basic living processes with reference to
green algae and aquatic, as well as terres-
trial plants (embryophytes). In addition,
he sometimes referred to plasmodial slime
molds (myxomycetes), and cited the work
of his colleague A. de Bary in this con-
text.
22
Fungi are rarely mentioned (they
were discussed in detail in de Bary’s
monograph of 1866), and bacteria are
absent in this 1865-book. This changed in
Figure 7. Scheme published by Julius Sachs in 1882, showing the basic body plan of an idealized
dicotyledonous seed plant (III), with the development of the embryo (I, II). Note that the growing
(meristematic) regions of this plant (buds, young leaves, root tips) are drawn in black/gray, whereas
the mature parts of the organism are white (adapted from ref.23).
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1872, after the plant scientist Ferdinand
Cohn had introduced these microbes
(“Schizomyceten,” also called “F€aulnis- or
Spaltpilze”) into the botanical literature.
Interestingly, in the revised-, updated
and extended version of his Experimental-
Physiologie, the Vorlesungen €uber Pflanzen-
Physiologie (Lectures on the Physiology of
Plants), Sachs (1882)
23
discussed green
plants (embryophytes), with reference to
an idealized “model organism” (Fig. 7), as
well as algae, lichens, fungi and bacteria
(Fig. 8A and B). In his Lecture XXIV,
Sachs (1882)
23
discussed the “F€aulnis- or
Spaltpilze” (Bakterien) with reference to
the work of F. Cohn. The author adopted
the then-popular idea that bacteria are
descendants of the hyphae of fungi (such
as Mucor), and that the tiny microbes can
also re-assemble to give rise to another
fungus. These non-green “lower plants”
(fungi and bacteria) are discussed with
respect to the destruction of wood and
other degenerative processes observed in
rotten plant material, as well as putrifica-
tion of fruits etc. Hence, Sachs (1882)
23
regarded both the fungi and bacteria as
pathogenic microorganisms that destroy
wood, fruits and other parts of healthy
plants. Beneficial microbes (symbionts)
are not mentioned by the author, although
Sachs’ colleague de Bary had discussed
symbiotic “plant-cyanobacteria” (Azolla/
Anabaena) interactions in several of his
publications.
22
Interestingly, Sachs (1882)
23
described
in detail the thallus of liverworts, such as
that of the widely distributed species
Marchantia polymorpha (Fig. 9A and B).
In this context, the botanist referred to the
gametophyte (i.e., the green plant body)
as representing the dominant phase of the
life cycle in this “primitive land plant”
and provided insights into the cellular
structure of this organism that is charac-
terized by dichotomously branched thalli
(with rhizoids attaching them to the soil)
that exhibit apical growth.
Ten years ago, it was discovered that the
vegetative growth of pieces of thalli (or iso-
lated vegetative propagules, the gemmae)
of liverworts, such as M. polymorpha, is pro-
moted by naturally-occurring, plant-
associated methylobacteria.
24
These a-pro-
teobacteria, which can be isolated/culti-
vated on agar-plates (Fig. 10A), consume
Figure 8. Drawings of the fungus Phycomyces nitens, with a network of hyphae (mycelium) and spo-
rangia (A). The groups of bacteria 1 to 4 were described by Julius Sachs in 1882 as Schizomycetes
(Spaltpilze) (B). Different morphotypes of bacteria are depicted schematically, with reference to the
work of F. Cohn (adapted from ref.23).
Figure 9. Julius Sachs frequently referred to “lower plants”(bryophytes etc.) to describe basic prin-
ciples of growth and reproduction. Morphology of part of the thallus of a mature liverwort (March-
antia polymorpha) (gametophyte), without stalked sporophytes (archegonia). Shallow cups with
disk-shaped gemmae (vegetative propagules) are visible (A). The cross-section through the thallus
shows a respiratory pore, the upper/lower epidermis, and mesophyll tissues (B) (adapted from
ref.23).
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methanol released by the growing plant
cells, and stimulate elongation growth of
their host organism via the biosynthesis/
secretion of phytohormones (auxins, cyto-
kinines).
25
Figure 10B shows the upper
surface of a thallus that grows rapidly in the
presence of methylobacteria. At larger mag-
nification, numerous epiphytic microbes
can be detected that are attached to the epi-
dermal cells of the liverwort via extra-cellu-
lar polymeric substances. Moreover, it is
obvious that these plant-associated methyl-
obacteria live in a social community,
referred to as a “bacterial biofilm”
(Fig. 10C). Based on these and other find-
ings, these microbes have been classified as
co-evolved phytosymbionts.
24-28
Julius Sachs’ younger colleague, the
German botanist Wilhelm Pfeffer (1845–
1920), elaborated and extended the Sach-
sian principle of controlled experimenta-
tion. Moreover, Pfeffer fully incorporated
bacteria as pathogens, commensals, or
cooperation partners of green plants into
botanical research. For instance, in his
textbook Pflanzenphysiologie (Vol. I,
1897/Vol. II, 1894),
29
Pfeffer discussed
Theodor Engelmann’s (1843–1909)
“bacteria-experiments” of 1882 for the
elucidation of the action spectrum of pho-
tosynthesis in filamentous green algae,
such as Oedogonium. This outstanding dis-
covery was not accepted by Sachs, who
responded with polemical remarks
directed against Engelmann (and others)
when these findings were published.
6
In addition, Pfeffer (1897/1904)
29
described the symbiotic relationship
between leguminous plants (Lupinus luteus
etc.) and soil-borne bacteria of the genus
Rhizobium with respect to nitrogen fixation.
Hence, Wilhelm Pfeffer was the most inno-
vative and creative successor of Julius Sachs,
so that it is appropriate to introduce the
term “Sachs-Pfeffer-Principle of Experi-
mental Plant Research.” However, in con-
trast to Sachs, who was a gifted author,
Pfeffer’s work is difficult to read, due to his
formal style. Nevertheless, Pfeffer should be
regarded as the co-founder of experimental
plant biology,
30
notably since he fully
incorporated the “microbiological aspects”
into this emerging scientific discipline.
Conclusions
In his Review of E. G. Pringsheim’s
monograph on Julius Sachs, the botanist and
psychologist Arthur Tansley (1871–1955)
summarized the rare combination of charac-
ters likely responsible for Sachs’ genius as
follows: 1. He was a great investigator with
the urge to go direct to nature and find out
for himself; 2. he was a gifted experimental-
ist, with the ability to devise and construct
his own apparatuses; 3. he had the true philo-
sophical mind which always and everywhere
seeks the general significance of particular
phenomena, and 4. he had the spirit of
the creative artist who aims at con-
structing an artistic whole from the
materials with which he works.
31
Hence, the specific quality of the publi-
cations authored by Julius Sachs may
rest on these 4 specific characters of the
great scientist (and philosopher/artist).
In 1866, Sachs left the Agricultural
College in Poppelsdorf/Bonn (Fig. 1) to
became, as successor of Anton de Bary,
Professor of botany at the University of
Freiburg i. Br., where he wrote his influen-
tial Lehrbuch der Botanik (Textbook of
Botany) (1868; 4. Ed. 1874).
32
After only
3 semesters, he accepted the chair of bot-
any at the University of Wuerzburg, where
he stayed until his death on May 29,
1897. In Wuerzburg, Sachs published a
book on the Geschichte der Botanik (His-
tory of Botany) (1875),
33
and his famous
Vorlesungen €uber Pflanzen-Physiologie (Lec-
tures on the Physiology of Plants) (1882;
2. Ed. 1887).
23
Figure 10. Photograph of a piece of the liverwort Marchantia polymorpha and agar plate-impressions, showing colonies of pink-pigmented methylobac-
teria isolated from the upper surface of the thallus (A). Scanning electron micrographs of the upper side of the thallus of M. polymorpha, with 3 respira-
tory pores (B). On the surface of the epidermal cells, and the margin of the pores, bacteria are attached. At 50-fold larger magnification, numerous
epiphytic microbes (Methylobacterium mesophilicum) become visible. These bacteria live in a super-cellular biofilm, in which individual prokaryotes are
attached to each other, and to the epidermal cells of the plant, via extracellular polymeric substances (thread-like structures) (C). Ba Dbacteria, Ep Depi-
dermis (unpublished results).
e1062958-8 Volume 10 Issue 9Plant Signaling & Behavior
Downloaded by [Universitaetsbibliothek Kassel] at 23:26 12 October 2015
Julius Sachs was the mentor of numer-
ous well-known botanists, such as Francis
Darwin and Wilhelm Pfeffer; he also
exerted a strong influence on Arthur Tans-
ley, who wrote, with reference to the
English version (1887) of Sachs’ Vorlesun-
gen, that “It was this translation, read
when it appeared in 1887, that first
attracted interest of the present reviewer,
as a boy, to scientific botany.” (ref.31). As
a result of his outstanding achievements,
Sachs received many honors and awards
during the second half of his professional
career. However, despite this world-wide
recognition, he remained a dedicated, cre-
ative, hard-working scientist and evolu-
tionist thorough his life.
34-36
Finally, it should be stressed that his
Vorlesungen, published in 1882, may be
interpreted as the “second, updated/
extended edition” of Sachs’ Experimental-
Physiologie of 1865. In this elegant, well-
illustrated book, wherein he published his
most famous drawing, a general scheme of
a dicotyledonous plant (Fig. 7), Sachs also
discussed bacteria with reference to the liv-
ing processes of angiosperms (Fig. 8).
However, it was Wilhelm Pfeffer, who
fully incorporated the “bacterial world”
into 19th-century botanical sciences.
Therefore, Pfeffer should be honored as
the co-founder of experimental plant
physiology, which can be defined in 2015
as “systems biology of photoautotrophic
organisms (embryophytes, algae, and
cyanobacteria).”
Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were
disclosed.
Funding
This project was supported by the
Alexander von Humboldt-Foundation
(Bonn, Germany) (AvH-Fellowship
Stanford-CA, USA, 2014/15 to U. K.).
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