Plant Morphology
by
Rolf Sattler
Continuum Morphology and Process Morphology
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
have 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) tends to be fragmenting and
categorical. 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
is
simple and useful 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
biology, although they may appear to be a narrow field,
can become universal.
In spite of the continuum within plants, in textbooks and
many research publications it is stated explicitly or
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,
it is obvious that we construct them through our
delimitations. These delimitations are not totally arbitrary.
But other delimitations that divide plants in different ways
are also possible (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*). For example, the leaf with a
continuous part of the stem below it can be considered a unit
of plant construction, and such a unit is neither more nor
less arbitrary than the units of leaf and stem.
Units that result from different delimitations are
complementary (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 article
“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. For example, 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 are partially A and B. In fuzzy
logic we express to what extent they are 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 to be only 51% phyllomes and
49% caulomes (stem homologues), which means that they are
about half way between typical phyllomes and caulomes
(Sattler and Jeune
1992, Appendix 5,
p. 261). (For my 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
homologous, if they occupy the same relative position within
the plant. Thus, what occurs in the axil of a leaf is a
shoot, and what subtends a shoot is 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 homologous to 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 only homotopous with axillary shoots, not homologous,
that is, they 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 are 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 are 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 are 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 are 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 contibutions
of Meyen that are especially relevant to 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), 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 is 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 is 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. 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
is
also
a process. Since it is a very slow process, it 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 is always in 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). Many of these 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). This is 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). 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 is 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 there is leafing, only activity,
instead of the leaf that as a leaf is static because it
remains a leaf in spite of all the processes that might
bring it closer to a shoot or stem.
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 does not
have
process(es), a
structure is
process(es).
Hence, no structure/process dualism. Nonetheless, the
structure/process dualism is a useful perspective on
biological phenomena, but its transcendence through process
morphology reveals the dynamics of organic form more
completely that 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 and plays a role in
evolutionary developmental biology (evo-devo) of plants
(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) is 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 is 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 are 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
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
dynamic: change is fundamental as in Buddhism that
emphasizes impermanence. Contextualism is also dynamic.
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 are 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 is appropriate. However, if we ask an either/or
question for an intermediate structure, we cannot find a
satisfactory answer because the question is inappropriate in
this particular situation. Therefore, before asking a
question, one has to examine whether it is appropriate.
Inappropriate questions are pseudo-questions because there is
no satisfactory answer 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, being 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 - is the
unmanifest source, the unnamable. Since it is unnamble, we
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, it is
mystery... "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 is beyond
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, his 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 are culture-dependent. Thus, to some extent,
the findings of science are a reflection of our culture.
Since Aritotelian either/or logic is still a fundamental
part of our mainstream culture, it is not surprising that
it is also characteristic of 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).
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 is 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 are 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.