Plant Morphology
Continuum
Morphology and Process Morphology
Rolf Sattler
Plant Morphology
deals with plant form, including its development and
evolution. It can be defined in a narrow sense as referring
only to external form, in contrast to anatomy that refers to
internal form. But plant morphology can also be defined in a
wide sense that includes both internal and external form at
all levels of organization from the molecular and cellular
level to the organismal level (Sattler, R. (ed.) 1978.
Theoretical Plant Morphology, Introduction).
Since molecular genetics has become fashionable, plant
morphology has been increasingly neglected. Nonetheless,
plant morphology remains fundamentally relevant to nearly all
fields of plant biology such as molecular genetics,
physiology, ecology, evolutionary biology and systematics. In
these fields morphological concepts and/or theories are used
or implied. Therefore, to some extent these fields are based
on or reflect morphology (Sattler and Rutishauser
1997).
Contrary to a widespread misconception, plant morphology is
not a finished science, but, like any science, open to
constant innovation. Such innovation may concern details or
concepts, theories, and even the disciplinary matrix (or
paradigm). My contributions to plant morphology have been
empirical and theoretical, involving a revision of some of
the most basic assumptions and tenets in the disciplinary
matrix of plant morphology (see also Yin-Yang and Dao
(Tao)).
With many undergraduate and graduate students, technicians,
postdoctoral fellows, research associates, and colleagues I
carried out research in plant morphology for nearly forty
years in the second half of the 20th
century (see
my Publications). One major
focus of this research has been the dynamic form continuum
in plants, especially flowering plants. A review of many
aspects of this research can be found in my book chapter
entitled “Homology, homeosis and process morphology in
plants” in B.K. Hall (ed). 1994. Homology: The
hierarchical basis of comparative biology. Academic Press,
pp. 423-475. What follows is a brief summary of this work
with some references that can be found in the list of my
publications.
Mainstream plant morphology (also
called classical plant
morphology) emphasizes
fragmentation and categorization. Thus, plants are
conceptually fragmented into organ systems such as the
shoot and root system, organs such as root, stem
(caulome), leaf (phyllome), and outgrowths of these organs
such as hairs (trichomes). Then the whole diversity of
plant form such as that of flowering plants is reduced to
categories of these fragments. Hence, every organ that is
encountered in flowering plants must be either a root, or
a stem, or a leaf, or homologous to any one of them.
Continuum Morphology - Although the
fragmenting approach of mainstream morphology
works to some
extent, it tends to obscure the continuum of plant form.
When we observe any one particular plant such as a
flowering plant, we cannot find a clear-cut boundary
between the root and the stem or the stem and the leaves.
Furthermore, we cannot find a clear-cut boundary between
the soil and the root or the leaves and the air. A close
microscopic inspection reveals what has been called the
Soil-Plant-Air Continuum (SPAC). Since animals and humans
breathe in the air of this continuum, they are also
included in it. With regard to various energies, this
continuum extends into ecosystems, Gaia, and the whole
universe. Thus, plant morphology and plant biology,
although they may seem narrow fields, can become
universal.
In spite of the continuum within plants, in textbooks and
many research publications it is stated explicitly or assumed
implicitly that plants such as flowering plants
consist
of
roots, stems, and leaves. This gives the impression that
roots, stems, and leaves actually exist as entities. However,
since there are no clear-cut boundaries between these organs,
we have to construct them through our delimitations. Although
these delimitations have a limited validity, they do not
constitute absolute discontinuities. Other delimitations that
divide plants in different ways can also be made. For
example, the leaf with a continuous part of the stem below it
can be considered a unit of plant construction (Cusset, G.
The conceptual bases of plant morphology. In Sattler, R.
(ed.) 1982. Axioms and
Principles of Plant Construction, pp.8
– 86 (also published in Vol. 31a of Acta Biotheoretica);
Rutishauser and Sattler 1985*).
Units that result from different delimitations complement
each other (Rutishauser and Sattler 1985). They illuminate
different complementary aspects of plant construction and
thus, together, provide a more comprehensive picture and
understanding than any one single set of units such as the
common root, stem and leaf units (for the concept of
complementarity see chapter 6
of Wilber’s
AQAL Map and Beyond, and my
post Perspectivism and Complementarity: AQAL,
the Big Tube, and the Dynamic
Mandala).
When we compare organs of different plants, we find that
although many of them can be grouped into categories such as
root, stem (caulome) and leaf (phyllome), there are also
intermediates between these categories. Thus, we find a
structural continuum not only within plants but also between
organ categories. This continuum even reaches beyond the
organ level to include higher and lower levels of the
structural hierarchy, thus leading to a new model of the
shoot (Sattler 1971, 1974), referred to as the pyramid model
of the shoot by Anthony and Sattler (1990).
According to this model, the typical shoot occupies the
top corner of the pyramid and the typical stem (caulome),
leaf (phyllome), and hair (trichome) the three bottom
corners of the tetrahedral pyramid. Intermediate
structures occur in the space between the four poles of
the tetrahedron (see Sattler. 1986. Biophilosophy,
p. 105). Using principal component analysis, we demonstrated
a continuum between roots, shoots, stems, leaves, and hairs
(Sattler and Jeune,
1992).
Nonetheless, as long as we consider only structures that fit
the structural categories, either/or thinking of our common
Aristotelian logic is applicable. Thus, a structure
belongs either to category A or B, an organ is either a
stem (caulome), or a leaf (phyllome). However, if we
consider the whole structural continuum, continuum
or fuzzy logic is required
because for intermediate structures it makes no longer
sense to ask whether they are essentially A or B; they are
neither A nor B; they represent partially A and B. In
fuzzy logic we express to what degree they represent A and
B. For example, the stamens of Commandra
umbellata (that in
mainstream plant morphology are interpreted as phyllomes,
that is, leaf homologues), according to principal
component analysis turn out as 51% phyllomes and 49%
caulomes (stem homologues) (Sattler and Jeune
1992, Appendix 5,
p. 261). (For a general discussion of fuzzy logic see Chapter 2
of Wilber’s
AQAL Map and Beyond. For
philosophical
issues of plant morphology see Chapter 5 of my
Biophilosophy
book (1986)
and my article “Some comments on the morphological,
scientific, philosophical and spiritual significance of
Agnes Arber’s life and work,” published in the Annals of
Botany 88: 1215-1217, 2001).
The existence of
intermediate structures has often been overlooked or denied
because of excessive and overriding weighting of the position
criterion. According to this criterion, structures are
considered homologous, if they occupy the same relative
position within the plant. Thus, what occurs in the axil of a
leaf is considered a shoot, and what subtends a shoot is
interpreted as a leaf. However, a simple thought experiment
shows that this kind of reasoning can lead to absurd
conclusions: for example, if we placed a leaf in the axil of
a leaf, it would have to be homologized with a shoot.
Obviously, this would not be a case of homology, but only
homotopy (same position). Similarly, intermediate structures
that we have found to occur in the axil of leaves are not
essentially shoots, nor are they derived from shoots only;
they are derived from the organs whose traits they share. For
example, if they combine leaf and stem traits, they are
derived from both leaves and stems: they represent hybrid
structures or mosaics (Sattler, R. 1988. Homeosis in plants).
We have much evidence that not only the quality but also the
relative position of structures may change, which means that
one structure can be totally or partially replaced by another
structure that may or may not be homologous. This phenomenon
is called homeosis. Examples of total homeosis: the
replacement of a stamen by a petal, or an axillary shoot by a
leaf (Sattler 1988; Lehmann and Sattler 1993). Examples of
partial homeosis: certain compound leaves that show a
combination of leaf and shoot features (Sattler and
Rutishauser 1992; Lacroix and Sattler 1994; Rutishauser and
Sattler 1997; Rutishauser and Isler
2001) and
therefore can be considered partially leaves and shoots
as Agnes Arber has pointed
out long ago in her Philosophy
of Plant Form (1950) whose
nearly 50th
anniversary
was celebrated in a symposium at the International
Botanical Congress in 1999. In this symposium,
Rutishauser and Isler (2001)
contrasted
Fuzzy Arberian Morphology (FAM) with the more restricted
Classical Morphology (CLAM). Serge Meyen's work also went
far beyond the limitations of classical morphology (see,
e.g., Meyen, S.V. 1987. Fundamentals
of Palaeobotany. London:
Chapman & Hall). Like Arber's work, the contributions
of Meyen (that focus on evolutionary plant morphology)
have not received the attention they deserve. However, my
own work has been much inspired by that of Serge Meyen
(whom I once met in Moscow at the International Botanical
Congress), Agnes Arber (whom I never met), and many
others.
In Fuzzy Arberian Morphology or continuum morphology the
concept of homology becomes also fuzzy. The question then is
not whether an intermediate structure is homologous with A or
B, but to what degree it appears homologous with A and B
(Sattler 1966; Sattler 1884. Homology - a continuing
challenge; Sattler 1994. Homology, homeosis and process
morphology in plants). However, for structures that fit the
categories, the common homology concept based on either/or
logic seems still applicable.
The claims of continuum morphology have been supported by
many detailed empirical investigations of shoot, leaf, and
flower development in a great diversity of flowering plants
(see my publications and those of
other authors such as Rutishauser and Isler
2001). The
complexity of developmental patterns that we presented in
my book Organogensis
of Flowers (1973) can
also be understood in terms of continuum morphology (see
also Flowers and
Mandalas)
Investigations in molecular genetics have provided some
support for continuum morphology. For example, it has been
shown that certain compound leaves combine gene activity that
is typical for shoot and leaf development (see below).
Therefore, these compound leaves are not only morphological
but also genetic mosaics, that is, intermediates between
leaves and shoots as postulated by Agnes Arber’s
partial-shoot theory of the leaf (Sattler and Rutishausr
1992; Rutishauser and Sattler 1997; Rutishauser and Isler
2001).
Process Morphology (Dynamic Morphology) - It can be
useful to make a distinction between structure and process:
for example, between the structure of a leaf and the
processes that occur within the leaf. However, upon close
inspection, we can see that the structure of the leaf changes
and therefore can be seen as a process. Since it changes very
slowly, this process is not easily noticeable, especially in
later developmental stages as the leaf approaches maturity.
But the leaf, like other structures, is never completely
static. It always undergoes a process of growth and/or decay,
differentiation and/or dedifferention. Within these four
basic morphogenetic processes, subprocesses can be
distinguished such as branching or symmetrisation. A whole
structure such as a leaf can then be seen as a combination of
processes, and the diversity of plant form can be understood
as a diversity of process combinations (Sattler 1988. A
dynamic multidimensional approach to floral morphology;
Sattler 1990. Towards a more dynamic plant
morphology; Sattler
1992. Process morphology: structural dynamics in
development and evolution; Sattler 1993. Why do we need a
more dynamic study of morphogenesis?; Sattler and
Rutishauser 1990. Structural and dynamic descriptions of
the development of Utricularia
foliosa and
U.
australis). Many of the
process combinations correspond to the typical organ
categories. However, since there are intermediates that do
not fit the categories, a continuum of process combination
occurs (Jeune and Sattler 1992). The result: the dynamic
form continuum of plants that I referred to above.
I called this dynamic approach to the study of plant form
process morphology or dynamic morphology (Sattler
1990). And I
applied it not only to plant development but also to the
evolution of plants (Sattler 1998. On the origin of
symmetry, branching and phyllotaxis in land plants).
Most of my publications, including my papers on
fusion and
continuity (Sattler 1978) and a new approach to gynoecial
morphology (Sattler 1974) deal with processes, but, like
almost all research in developmental and evolutionary plant
biology, still imply a structure/process dichotomy.
One reason, maybe the main reason, why we imply so easily a
structure/process dualism resides in the structure of our
language. Most languages, including the English language,
have a noun-verb or subject-verb-object structure in which
nouns refer to things such as leaves and verbs to processes
such as the processes of leaves (Sattler 1993. Why do we need
a more dynamic study of morphogenesis?) If we could devise a
language that is based on verbs only, we would have a
pure process language
that would no
longer imply a structure/process dualism. Then we could
easily recognize that what we call a leaf constitutes
leafing, only activity.
In his Biological
Principles (1967, p. 330),
J.H. Woodger characterized the aim of process morphology very
succinctly in very general terms when he wrote: "what is
required is an enlargement of our concept of 'structure' so
as to include and recognize that in the living organism it is
not merely a question of spatial structure with an 'activity'
as something over it, but that the concrete organism is a
spatio-tempotal
structure and
that this spatio-temporal structure is
the
activity itself." In other words: a structure is not seen as
having processes, a structure is seen as process(es). Hence,
no structure/process dualism. Nonetheless, the
structure/process dualism remains a useful perspective on
biological phenomena, but its transcendence through process
morphology reveals the dynamics of organic form more
completely than the structure/process dualism inherent in
mainstream biology.
Outlook
-
Although continuum and process morphology have not yet become
mainstream because they are too different from deeply
ingrained modes of thinking in our culture and science, they
remain an active area of research in the
21st
century.
Denis Barabé, Bernard Jeune, Christian
Lacroix,
Rolf Rutishauser, and others
continue research on the dynamic continuum of plant form.
Furthermore, the dynamic continuum is validated by
investigations in molecular genetics. For example,
Hirayama et al (2007) showed that the phylloclade
in Ruscus aculeatus
"is not
homologous to either the shoot or the leaf, but that it
has a double organ identity," which means that it combines
shoot and leaf processes (as has been documented on purely
morphological grounds by Cooney-Sovetts and Sattler
over twenty
years ago). Eckardt and Baum (2010) concluded that "it is
now generally accepted that compound leaves express both
leaf and shoot properties." (Some morphologists, including
myself, reached this conclusion long ago by purely
morphological
investigations (see Rutishauser and Isler
2001). Finally,
continuum and process morphology also play a role
in
plant evo-devo (evolutionary developmental
biology) (see, e.g.,
Vergara-Silva, F. 2003. Plants and the Conceptual
Articulation of Evolutionary Developmental Biology. Biology
and Philosophy 18: 249-284).
Plant Morphology and Philosophy - Many plant
morphologists and other scientists believe that science
operates independently of philosophy. But it has been shown
that science and philosophy remain intertwined: science
includes philosophical assumptions and receives input from
philosophy. Journals such as Biology and Philosophy
are devoted to
the relation between biological science and philosophy.
One philosophical assumption in mainstream plant morphology
(classical plant morphology) involves essentialism (Sattler
1977. Essentialism in plant morphology) or, if not
essentialism, at least Aristotelean either/or logic, the
belief that any organ of plants such as flowering plants must
be either a root, a stem (caulome) or leaf (phyllome), which
means that even if an organ does not clearly fit these
categories, it belongs nonetheless to one or the other
(Sattler, R. 1986. Biophilosophy).
The insistence on either/or supposedly has been justified by
the phylogenetic interpretation of homology. It is argued,
for example, that even if a structure appears to be an
intermediate between a stem and a leaf, it evolved from
either one or the other. However, in a strict sense,
structures do not evolve from each other, that is, there is
not direct phylogenetic connection between structures
(Sattler 1984. Homology - a continuing challenge, p. 386).
The phylogenetic connection or lineage is between organisms
or populations. As has been known for a long time and as it
is emphasized in evolutionary developmental biology, the
development of organisms may change during evolution in such
a way that elements of different developmental pathways may
be combined. For example, it has been shown that certain
compound leaves combine leaf and shoot processes, including
genes that are associated with these processes (see,
e.g., Rutishauser and Isler,
2001). Therefore,
these compound leaves can be seen as partially homologous
with leaves and
shoots. The
insistence in mainstream plant morphology that they are
essentially leaves obscures their partial homology.
Most philosophers of science and biologists deny that
essentialism still plays a role in mainstream thinking.
However, listening to colleagues I have heard again and again
expressions such as "but essentially it is this." Similar
expressions one can often hear in everyday life, which to me
indicates that essentialism is still deeply rooted in our
culture.
Continuum morphology also freed itself from the constraints
of Aristotelian either/or logic that is still
taken for granted to a great extent in science and
society. The logic of continuum morphology is
fuzzy logic, or at least
a more-or-less logic instead of or in addition to
either/or logic.
Process morphology has incorporated ideas of
process philosophy and
contextualism. According to process philosophy, reality is
seen as dynamic as in Buddhism that
emphasizes impermanence. Contextualism also implies
change: events are placed into the context of other events
that may reach universal dimensions. For example, events
(processes) that constitute a leaf (leafing), are
intertwined with solar and cosmic radiation. Thus, the
leaf (leafing) reaches cosmic dimensions. Since the
integration is not limited to physical events but includes
also subtle and very subtle events, it reaches even kosmic
dimensions - kosmic, in contrast to cosmic, comprises
matter, mind, and spirit (see the Prologue of
Wilber's AQAL Map and
Beyond). Because of
the emphasis on integration, contextualism tends
towards organicism and
holism (Sattler, R.
1986. Biophiolosophy. Analytic and Holistic Perspectives,
p. 245) (see also Ways of Thinking
in
my book ms Healing
Thinking and Being).
The
Importance of Questions - In a sense,
questions seem more important or more fundamental than
answers because the questions we ask determine to a great
extent the kind of answers we obtain. If we ask an either/or
question as it is typical for mainstream plant morphology and
much thinking in science and society, the answer, if any, is
in terms of a category. For typical structures, this kind of
question seems appropriate. However, if we ask an either/or
question for an intermediate structure, we cannot find a
satisfactory answer because the question seems inappropriate
in this particular situation. Therefore, before asking a
question, one has to examine whether it appears appropriate.
Inappropriate questions have been called pseudo-questions
because we cannot obtain satisfactory answers to these
questions. Such questions obstruct progress. Recognizing
pseudo-questions and posing new meaningful questions has led
to great innovations in science and society.
Plant
Morphology and Spirituality - A number of books
on the relation between science and spirituality have been
published, and symposia have been organized around this
topic. In a symposium entitled "Divergence and Convergence of
Sciences and Spirituality" that was dedicated to the Dalai
Lama on the occasion of his 60th birthday on July 6, 1995, I
discussed the relation of life science and spirituality
(Sattler 1999. Divergence and convergence of sciences and
spirituality: life science and spirituality). Already in
1976, I taught a summer course on "Modern Biology and Zen" at
Naropa Institute in Boulder, Colorado. In this course, I
explored no-thingness in biology, including plant morphology,
and its relation to nothingness or
emptiness in Buddhism,
especially Zen. No-thingness means that
there are no separate things but a continuum,
undivided wholeness. As I pointed
out above, a plant does not consists of things or entities
such as organs. We create these things through our
delimitations. Without these delimitations, there is
no-thing. Also, the plant itself is no-thing, since it is
fully integrated with its environment (see SPAC above).
Instead of no-thingness, we could refer to undivided
wholeness, unity, or oneness, all of which play a central
role in holistic science and
spirituality,
especially mysticism - hence a
convergence of science and spirituality. Barbara
McClintock, the 1983 Nobel Laureate in Physiology or
Medicine, as a plant geneticist and
mystic,
exemplified this convergence when she wrote: "Basically,
everything is one. There is no way in which you draw a
line between things. What we [normally] do is to make
these subdivisions, but they're not real. Our educational
system is full of subdivisions that are artificial, that
shouldn't be there" (quoted in Evelyn Fox Keller.1983. A
Feeling for the Organism. The Life and Work of Barbara
McClintock. Freeman, New York, p. 204).
There remains, however, also a difference between science and
spirituality as mysticism. The scientist, especially the
holistic scientist, has intellectual knowledge of
nothingness, undivided wholeness, unity and oneness. The
mystic experiences or is
nothingness,
undivided wholeness, unity, and oneness (Sattler 1977, 1999:
see above).
Nothingness, undivided wholeness, unity and oneness in
science as well as in process philosophy and process
morphology refer to manifest reality that can be investigated
through our senses and the thinking mind. However, beyond
manifest reality - but not separate from it - we can find the
unmanifest source, the unnamable. Since it cannot be named,
one cannot say that it is dynamic or static, discontinuous or
continuous, fragmented or whole. We cannot even say that it
is both dynamic and static, discontinuous and continuous,
fragmented and whole. It is beyond words and concepts, and
therefore it appears mysterious... "The Tao that can be told
is not the eternal Tao...The unnamable is the eternally real"
(Tao Te Ching, translated by Stephen Mitchell.
HarperPerennial, 1992)..
Most scientists, especially mechanistic mainstream
scientists, including mainstream plant morphologists, shy
away from or denigrate mystery. However, some of the greatest
scientists recognize that beyond that which can be grasped by
the intellect lies the unfathomable mystery that transcends
science but can inspire scientists. For example, Albert
Einstein, the great physicist, wrote: "The most beautiful
thing we can experience is the mysterious. It is the source
of all true art and science"(quoted by Ravi Ravindra.
2000. Science and
the Sacred. The
Theosophical Publishing House, Wheaton, IL,USA)
Plant
Morphology in Relation to the Theme of my
Website. - You might ask
whether plant morphology relates to “Ken Wilber, the AQAL
Map, Health and Laughter,” the title of my website. Yes,
indeed it relates in many ways. Let me briefly mention the
following:
1.
Ken Wilber severely
criticized the myth of the given, “the belief
that reality is simply given to me…instead of a
world that is con-structured in various ways before it
ever reaches my empirical or phenomenal awareness” (Ken
Wilber. 2006. Integral Spirituality, p. 176). We find an
expression of this myth of the given in mainstream plant
morphology where it is often taken for granted that plants
such as flowering plants consist
of
roots, stem(s), and leaves. But as I have pointed out,
these organs are constructed through our delimitations –
they are not given by nature. As Ken Wilber and others,
especially postmodern authors, have emphasized, our
constructions reflect our culture. Since Aritotelian
either/or logic consitutes still a fundamental part of our
mainstream culture, it is reflected in mainstream plant
morphology and its central concept, the concept of
homology. However, for a long time, at least a few plant
morphologists have gone beyond either/or thinking (see
Cusset, G. The conceptual bases of plant morphology. In
Sattler, R. (ed).1982. Axioms and
Principles of Plant Construction, pp.
8-86; Rutishauser and Isler
2001).
Unfortunately, their innovations have not been
incorporated into mainstream plant morphology.
2. Ken Wilber’s
AQAL map is hierarchical
(holarchical) with regard to the basic levels (structure
stages) of manifest reality. He states that organisms are
composed of cells, which are composed of molecules, which are
composed of atoms. According to a more refined version of
this hierarchical view, organisms are composed of organ
systems, composed of organs, composed of tissues, composed of
cells, etc. Thus, plants such as flowering plants are
composed of the root system and shoot, the former is composed
of roots, the latter of stems and leaves (and their
homologues). Furthermore, all organs may have trichomes
(hairs), which are tissue outgrowths. Thus, we are dealing
here with three levels of the hierarchy of plant
construction: organ systems, organs, and tissues. As I
pointed out above, we found a continuum between these three
levels of the hierarchy, which means that the hierarchy
collapses at these levels, since a hierarchy requires levels
(Sattler and Jeune 1992; Jeune and Sattler 1992). I have
shown that the hierarchy can also be collapsed at other
levels (see Wilber’s AQAL Map and
Beyond, Chapter 1). This does
not mean that hierarchical thinking is completely useless,
but it is limited and therefore needs to be complemented
by other ways of thinking
such as
continuum thinking (fuzzy logic).
3. In Chinese medicine health means balance. This notion is
applied to our physical, emotional, and spiritual health. It
can also be applied to plant morphology. Recognizing only the
root-stem-leaf delimitations of plants such as flowering
plants and treating them as given appears one-sided and
unbalanced. But recognizing complementary delimitations
creates more balance and thus a healthier plant morphology.
Furthermore, recognizing and applying healing ways of
thinking (healing
logic) can heal the wounds and conflicts that have been
inflicted by an insistence on Aristotelian either/or
logic, especially in cases of a continuum where it does
not apply.
4. Plant morphologists who embrace the root-stem-leaf
delimitations of plants such as flowering plants seem often
dead serious, and sometimes even aggressive and outright
nasty, in its defense. Unfortunately, such behavior is not
restricted to plant morphology but occurs also in many other
areas of science, philosophy, ideology, and religion. If we
could go beyond the myth of the given and recognize the
relativity of different views (which does not mean that they
are necessarily equally valid; see, for example,
Sattler 2009), we could
inject lightness, humor and laughter into this exaggerated
seriousness, which would be healing not only for
individuals but also for the scientific community, society
and the planet (see, for example, laughter yoga).
*For references without the title see under Refereed Papers
in the list of my publications. For
references with the title see under Book Chapters and
Symposium Contributions in the same list.
See also
The
Evolution of my Morphological Thinking Documented through
my Publications and Plant Evo-Devo (Evolutionary
Developmental Biology),
From
Plant Morphology to Infinite Issues (including Ken Wilber
and Korzybski) and
Science:its
Power and LImitations