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The following manuscript was accepted as a guest editorial by American Bi=
ology Teacher editor Randy Moore in November 2002. However, the Managing =
Editor much later informed me that the manucript had been misplaced and w=
ould not be published because she felt it was no longer timely. Appeals t=
o the new Editor, Publisher, NABT President and ABT Journal Advisory Comm=
ittee 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 mere=
ly an "animal metaphor". However, Trewavas (2002) was not being metaphori=
cal, he was being literal. Flannery (2002) arbitrarily restricted the ter=
m intelligence to "an animal way of doing things." However, Webster's dic=
tionaries 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) descri=
bed how plants cope with new or trying situations such as high temperatur=
es, water deprivation, and attacks by herbivores and pathogens. Therefore=
, no "animal metaphor" is required. Plants literally fit a dictionary def=
inition 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 qu=
alifies as intelligence according to the dictionary definition.
Flannery (2002) stated that all animals, "even a slug", have higher IQs t=
han any plant. However, several plant species are intelligent enough to p=
roduce caffeine, which Flannery (2002) noted is a highly effective pestic=
ide against slugs. Was the inventor of Velcro, George de Mestral, more in=
telligent than the cocklebur (Xanthium stumarium) which gave him the idea=
(Jacobs 1996)? Was Joseph Paxton, the designer of London's famous Crysta=
l Palace of 1851, more intelligent than the giant waterlily (Victoria ama=
zonica) whose leaf venation inspired his design (Carter 1985)? Are the ch=
emists who first synthesized taxol in the laboratory more intelligent tha=
n the Pacific yew (Taxus brevifolia) which synthesized it first and provi=
ded 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 t=
hat were really made by plants. Many peop
le 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 "try=
ing 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 wi=
ped out, plants would actually benefit in several ways because they could=
recolonize all the areas occupied by buildings and paving and would no l=
onger have the destructive effects of humans destroying their habitats, o=
vercollecting wild plant species into extinction, introducing nonnative i=
nvasive plants, and polluting the air, water and soil. Even if all animal=
s were wiped out, the many plant species that do not depend on animals fo=
r pollination and seed dispersal would not be negatively impacted. Even m=
any of the plants that coevolved with animals might be able to survive wi=
Common themes in science fiction, and goals of real science, are human cl=
oning and suspended animation for long space voyages. However, plants hav=
e 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 p=
lantlets, apomictic seeds, bulbs, corms, fragmentation, layering, rhizome=
s, runners, suckers, and tubers.
Flannery (2002) noted the "problem" Trewavas (2002) was addressing as "th=
e view of plants as passive and therefore not very interesting organisms"=
=2E However, Trewavas (2002) was only dealing with the view of plants as =
passive. He never stated or implied that plants were "not very interestin=
g." Given that Flannery (1999) wrote a column on plant blindness, it woul=
d have been much more desirable to have stated the problem more accuratel=
y, i.e. "Although a common misconception, it is a huge mistake to view pl=
ants 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=
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 st=
eal from their host trees (Benzing 1980). Plants may be stationary but th=
eir 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 di=
scharge its seeds up to 100 m (Ray et al. 1983).
Plants also face hordes of herbivores and pathogens, resource shortages a=
nd harsh environments. It is hardly passive that plants use a multitude o=
f mechanical and chemical weapons and ally themselves with a variety of b=
acteria, fungi and animals in their battle for survival. Their allies inc=
lude nitrogen-fixing bacteria, mycorrhizal fungi, animal pollinators, ani=
mal seed dispersers, fungal and bacterial endophytes and even ants that s=
erve as live-in bodyguards. Plants not only communicate with other plants=
, they communicate with their allies. For example, an Acacia tree produce=
s a chemical in its flowers that tells its ant bodyguards not to attack t=
he insect pollinators that visit the flowers (Ghazoul 2001).
The sizzling sex life of plants is hardly passive either. Plants flaunt t=
heir sex organs and often advertise them with flashy petals or bracts, de=
licious fragrances or a horrible stench. Some flowers even generate heat =
to attract pollinators or better disperse floral scents (Seymour 1997). J=
ack-in-the-pulpit (Arisaema triphyllum) changes its sex depending on the =
resources available (Policansky 1987). Plants fill the air with untold tr=
illions of pollen grains. Plants sometimes even trick animals into pollin=
ating their flowers or dispersing their seeds without giving them the exp=
Contrary to Flannery (2002), I think it is a fundamental requirement that=
students be able to contrast animal and plant strategies to deal with ba=
sic challenges, such as energy accumulation, environmental sensing, solid=
and liquid intake, gas exchange, waste disposal, internal transport, mec=
hanical support, temperature control, defense, growth and reproduction. I=
f students are not able to describe how plants meet these basic biologica=
l challenges, then they are suffering from plant blindness. Darley (1990)=
noted that plants' nutritional mode requires them to be stationary becau=
se they are "collectors and concentrators" and concluded that "If we feel=
animals are superior, it is only because we are animal chauvinists". Whe=
ther called animal chauvinism, plant blindness or plant neglect (Hershey =
1993, 2002, Hoekstra 2000, Wandersee and Schussler 1999), the problem rem=
ains that there are many biology teachers, and thus their students, "whos=
e familiarity with plants is little more=20
than skin-deep" (Nichols 1919). Perhaps Trewavas (2002) discovery that p=
lants are intelligent will make biology teachers take plants a bit more s=
David R. Hershey
dh321 at excite.com
Agnes, M. E. (2002). Webster's New World Compact Desk Dictionary and Styl=
e Guide. New York: Hungry Minds.
Benzing, D.H. (1980). Biology of the Bromeliads. Eureka, California: Mad =
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 Biol=
ogy 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 co=
nflicts. 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 u=
s." Plant Science Bulletin, 48, 78-85.
Hoekstra, B. (2000). Plant blindness: The ultimate challenge to botanists=
=2E 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 elem=
entary botany and zoology in American colleges and universities. Science,=
Policansky, D. (1987). Sex choice and reproductive costs in jack-in-the-p=
ulpit, BioScience, 37, 476-481.
Ray, P.M., Steeves, T.A. and Fultz, S.A. (1983). Botany. Philadelphia: Sa=
Seymour, R.S. (1997). Plants that warm themselves. Scientific American, 2=
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 Academ=
y of Sciences, 96, 4216-4218.
Trewavas, A. (2002). Mindless mastery, Nature, 415, 841.
Wandersee, J.H. and Schussler, E.E. (1999). Preventing plant blindness. A=
merican Biology Teacher, 61, 82, 84, 86.
Woolfe, H.B. (1973). Webster's New Collegiate Dictionary. Springfield, Ma=
ssachusetts: G. and C. Merriam Company.
Addendum: After the above Guest Editorial was written, Dr. Trewavas publi=
shed a detailed invited review on plant intelligence which is available o=
Trewavas, A. 2003. Aspects of plant intelligence. Annals of Botany 92: 1-=
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