dh321 at excite.com
Organization: BIOSCI/MRC Rosalind Franklin Centre for Genomics Research
To: bionet-plants-education at net.bio.net
Newsgroups: bionet.plants.education
[I guess that didn't work! If this doesn't look better I'm giving up.
- moderator]
The following manuscript was accepted as a guest editorial by American
Biology Teacher editor Randy Moore in November 2002. However, the
Managing Editor much later informed me that the manuscript had been
misplaced and would not be published because she felt it was no longer
timely. Appeals to the new Editor, Publisher, NABT President and ABT
Journal Advisory Committee were acarpous so I thought I would make it
available here.
David R. Hershey
dh321 at excite.com
Plants Are Indeed Intelligent
Biology Today columnist Maura Flannery (2002) rejected Anthony Trewavas
(2002) thesis that plants have intelligence mainly by assuming it was
merely an "animal metaphor". However, Trewavas (2002) was not being
metaphorical, he was being literal. Flannery (2002) arbitrarily
restricted the term intelligence to "an animal way of doing things."
However, Webster's dictionaries don't restrict intelligence to animals.
Webster's dictionaries define intelligence as "the ability to cope with
a new situation" (Agnes 2002) or "the ability to learn or understand or
to deal with new or trying situations" (Woolf 1973). Flannery (2002)
described how plants cope with new or trying situations such as high
temperatures, water deprivation, and attacks by herbivores and
pathogens. Therefore, no "animal metaphor" is required. Plants literally
fit a dictionary definition of intelligence. Trewavas (2002) said
effectively the same thing as Webster; plants are intelligent because
they have "adaptively variable behavior." Trewavas (1999) has evidence
that plants learn, which also qualifies as intelligence according to the
dictionary definition.
Flannery (2002) stated that all animals, "even a slug", have higher IQs
than any plant. However, several plant species are intelligent enough to
produce caffeine, which Flannery (2002) noted is a highly effective
pesticide against slugs. Was the inventor of Velcro, George de Mestral,
more intelligent than the cocklebur (Xanthium stumarium) which gave him
the idea (Jacobs 1996)? Was Joseph Paxton, the designer of London's
famous Crystal Palace of 1851, more intelligent than the giant waterlily
(Victoria amazonica) whose leaf venation inspired his design (Carter
1985)? Are the chemists who first synthesized taxol in the laboratory
more intelligent than the Pacific yew (Taxus brevifolia) which
synthesized it first and provided them with the structure of taxol? Are
the thousands of plant products in a supermarket just an indication of
human accomplishment or do plants deserve some credit? Humans often take
sole credit for accomplishments that were really made by plants. Many
people do not seem to realize that "Man and all other animals are in
reality guests of plants on this earth" (Karling 1956).
If the modern Plant Kingdom, consisting of bryophytes and vascular
plants, was suddenly wiped out, humans would not be able to respond to
the "trying situation" without mass starvation. Humans might even go
extinct due to wars over, or overexploitation of, the remaining food
chains anchored by algae and photosynthetic bacteria. However, if humans
were suddenly wiped out, plants would actually benefit in several ways
because they could recolonize all the areas occupied by buildings and
paving and would no longer have the destructive effects of humans
destroying their habitats, overcollecting wild plant species into
extinction, introducing nonnative invasive plants, and polluting the
air, water and soil. Even if all animals were wiped out, the many plant
species that do not depend on animals for pollination and seed dispersal
would not be negatively impacted. Even many of the plants that coevolved
with animals might be able to survive without them.
Common themes in science fiction, and goals of real science, are human
cloning and suspended animation for long space voyages. However, plants
have used cloning and suspended animation for over 100 million years.
Seeds can survive in suspended animation for decades or centuries
(Shen-Miller et al. 1995). Plants have numerous cloning methods such as
adventitious plantlets, apomictic seeds, bulbs, corms, fragmentation,
layering, rhizomes, runners, suckers, and tubers.
Flannery (2002) noted the "problem" Trewavas (2002) was addressing as
"the view of plants as passive and therefore not very interesting
organisms". However, Trewavas (2002) was only dealing with the view of
plants as passive. He never stated or implied that plants were "not very
interesting." Given that Flannery (1999) wrote a column on plant
blindness, it would have been much more desirable to have stated the
problem more accurately, i.e. "Although a common misconception, it is a
huge mistake to view plants as passive or uninteresting." Flannery
(1999) actually dismissed the misconception of plants as uninteresting
rather well when she asked "Why deprive ourselves of the joy of learning
about organisms that have come up with so many fascinating strategies to
deal with the challenge of life on Earth."
How can parasitic and carnivorous plants be considered passive when they
are stealing energy and nutrients from other plants or murdering
animals, respectively? The strangler figs (Ficus aurea and other Ficus
spp.) are notorious for murdering their host trees. Plants are
constantly battling each other to the death. Even seemingly harmless
epiphytes are considered "nutritional pirates" who intercept mineral
nutrients and effectively steal from their host trees (Benzing 1980).
Plants may be stationary but their seeds or fruits may fly, float, be
forcibly discharged or carried by animals to other locations. Fruits of
coconut (Cocos nucifera) may float for hundreds of km in the ocean, and
the fruit of the sandbox tree (Hura crepitans) explodes like a hand
grenade when it dries and can forcibly discharge its seeds up to 100 m
(Ray et al. 1983).
Plants also face hordes of herbivores and pathogens, resource shortages
and harsh environments. It is hardly passive that plants use a multitude
of mechanical and chemical weapons and ally themselves with a variety of
bacteria, fungi and animals in their battle for survival. Their allies
include nitrogen-fixing bacteria, mycorrhizal fungi, animal pollinators,
animal seed dispersers, fungal and bacterial endophytes and even ants
that serve as live-in bodyguards. Plants not only communicate with other
plants, they communicate with their allies. For example, an Acacia tree
produces a chemical in its flowers that tells its ant bodyguards not to
attack the insect pollinators that visit the flowers (Ghazoul 2001).
The sizzling sex life of plants is hardly passive either. Plants flaunt
their sex organs and often advertise them with flashy petals or bracts,
delicious fragrances or a horrible stench. Some flowers even generate
heat to attract pollinators or better disperse floral scents (Seymour
1997). Jack-in-the-pulpit (Arisaema triphyllum) changes its sex
depending on the resources available (Policansky 1987). Plants fill the
air with untold trillions of pollen grains. Plants sometimes even trick
animals into pollinating their flowers or dispersing their seeds without
giving them the expected rewards.
Contrary to Flannery (2002), I think it is a fundamental requirement
that students be able to contrast animal and plant strategies to deal
with basic challenges, such as energy accumulation, environmental
sensing, solid and liquid intake, gas exchange, waste disposal, internal
transport, mechanical support, temperature control, defense, growth and
reproduction. If students are not able to describe how plants meet these
basic biological challenges, then they are suffering from plant
blindness. Darley (1990) noted that plants' nutritional mode requires
them to be stationary because they are "collectors and concentrators"
and concluded that "If we feel animals are superior, it is only because
we are animal chauvinists". Whether called animal chauvinism, plant
blindness or plant neglect (Hershey 1993, 2002, Hoekstra 2000, Wandersee
and Schussler 1999), the problem remains that there are many biology
teachers, and thus their students, "whose familiarity with plants is
little more than skin-deep" (Nichols 1919). Perhaps Trewavas (2002)
discovery that plants are intelligent will make biology teachers take
plants a bit more seriously.
David R. Hershey
dh321 at excite.com
Literature Cited
Agnes, M. E. (2002). Webster's New World Compact Desk Dictionary and
Style Guide. New York: Hungry Minds.
Benzing, D.H. (1980). Biology of the Bromeliads. Eureka, California: Mad
River Press.
Carter, T. (1985). The Victorian Garden. New York: Salem House.
Darley, W.M. (1990). The essence of "plantness." American Biology
Teacher, 52, 354-357.
Flannery, M.C. (1999). Seeing plants a little more clearly. American
Biology Teacher, 61, 303-307.
Flannery, M.C. (2002). Do plants have to be intelligent? American
Biology Teacher, 64, 628-633.
Ghazoul, J. (2001). Can floral repellents pre-empt potential ant-plant
conflicts. Ecology Letters, 4, 295-299.
Hershey, D.R. (1993). Prejudices against plant biology. American Biology
Teacher, 55, 5-6.
Hershey, D.R. (2002). Plant blindness: "We have met the enemy and he is
us." Plant Science Bulletin, 48, 78-85.
Hoekstra, B. (2000). Plant blindness: The ultimate challenge to
botanists. American Biology Teacher, 62, 82-83.
Jacobs, M.I. (1996). Unzipping Velcro. Scientific American, 274(4), 116.
Karling, J.S. (1956). Plants and man. American Biology Teacher, 18, 9-13.
Nichols, G.E. (1919). The general biology course and the teaching of
elementary botany and zoology in American colleges and universities.
Science, 50, 509-517.
Policansky, D. (1987). Sex choice and reproductive costs in
jack-in-the-pulpit, BioScience, 37, 476-481.
Ray, P.M., Steeves, T.A. and Fultz, S.A. (1983). Botany. Philadelphia:
Saunders.
Seymour, R.S. (1997). Plants that warm themselves. Scientific American,
276(3), 104-109.
Shen-Miller, J., Mudgett, M.B., Schopf, J.W., Clarke, S. and Berger, R.
(1995). Exceptional seed longevity and robust growth: Ancient sacred
lotus from China. American Journal of Botany, 82, 1367-1380.
Trewavas, A, (1999). How plants learn. Proceedings of the National
Academy of Sciences, 96, 4216-4218.
Trewavas, A. (2002). Mindless mastery, Nature, 415, 841.
Wandersee, J.H. and Schussler, E.E. (1999). Preventing plant blindness.
American Biology Teacher, 61, 82, 84, 86.
Woolfe, H.B. (1973). Webster's New Collegiate Dictionary. Springfield,
Massachusetts: G. and C. Merriam Company.
-----------------------------
Addendum: After the above Guest Editorial was written, Dr. Trewavas
published a detailed invited review on plant intelligence which is
available online:
Trewavas, A. 2003. Aspects of plant intelligence. Annals of Botany 92: 1-20
http://aob.oupjournals.org/cgi/content/full/92/1/1
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