Even we avid gardeners take plants for granted. Until they succumb to
disease because we put them in the wrong place or at the wrong time.
We can't know too much about them. And never will.
Btw, should you ever have the opportunity to attend a talk by Peter
Raven, take it. He is of vibrant energy, penultimately impassioned of
plants, and profoundly informative. At an event I attended, questions
from the audience included one to his attending mother: "Has he
always been like this?" She answered in the affirmative, with a
knowing smile.
Green, Life-Giving and Forever Young
By NATALIE ANGIER
Published: April 17, 2007
Show somebody a painting of a verdant, botanically explicit forest
with three elk grazing in the middle and ask what the picture is
about, and the average viewer will answer, “Three elk grazing.” Add a
blue jay to the scene and the response becomes, “Three elk grazing
under the watchful eye of a blue jay.”
What you’re unlikely to hear is anything akin to, “It’s a classic
temperate mix of maple, birch and beech trees, and here’s a
spectacular basswood and, whoa, an American elm that shows no sign of
fungal infestation and, oh yeah, three elk and a blue jay.”
According to Peter H. Raven, director of the Missouri Botanical
Garden, many of us suffer from an insidious condition called “plant
blindness.” We barely notice plants, can rarely identify them and
find them incomparably inert. Do you think that you will ever see a
coma as vegetative as a tree? “Animals are much more vivid to the
average person than plants are,” Dr. Raven said, “and some people
aren’t even sure that plants are alive.”
But the antidote to plant apathy is at hand. As an unusually cool,
sodden April edges toward May and spring’s cheeky blooms can be
bridled no longer, botanists urge everyone to venture outside and
check out the world through nature’s rose-colored glasses — and the
daffodil, cherry blossom, dogwood and lupine ones, too. If this view
doesn’t move you, you’re pushing up daisies.
As it happens, plants are not only alive in their own right. They are
also the basis of virtually all life on earth, including ours. The
core feature of planthood is autotrophy, that is, the happy ability
to make one’s own food. Plants essentially eat the sun, transforming
solar energy into sugars and starch through the stepwise enzymatic
stitchery of photosynthesis. Animals, by contrast, are heterotrophs,
defined by their need to devour other organisms — the hard-won fruit
and fiber of the suneaters, or the once-removed flesh of herbivores.
Moreover, because plants release oxygen as a byproduct of
photosynthesis, plants also give us aerobes leave to breathe. Our
atmosphere is currently about 20 percent oxygen, all of it the bounty
of the planet’s green-skinned autotrophs. “The most important
chemical reaction on earth is photosynthesis,” said Robert DeFeo,
chief horticulturist for the National Park Service. “We are all
parasites upon it.”
Essential though plants may be to our survival, Dr. Raven emphasizes
that they are a radically different form of organism than are
animals. Plants and animals have evolved along separate paths for
hundreds of millions of years, ever since single cells began pooling
their talents into multicelled beings. “Plants have evolved their
multicellularity completely separately from animals, and any direct
comparisons between the groups are wrong,” Dr. Raven said. “It’s as
if plants evolved on Mars, and animals here.”
In addition to their caloric self-sufficiency, plants can be envied
for their eternal youthfulness. A plant elongates itself through
constant cell growth in two zones of its body, at the very tips of
the roots, which grow down into soil or other surface to which the
plant clings, and the outer tips of the shoots, from which new
leaves, flowers and fruits sprout. Whereas an animal, upon reaching
maturity, has almost no young cells left in its body, Dr. Raven said,
“in plants the ends of the roots and shoots are always juvenile,
always growing, always babies.”
A plant is also always drinking, slurping water and nutrients the
only way it can, through its roots. Everything needs water to
survive, but another radical difference between the faunal and floral
crafts is that while we can drink water and keep it circulating
through the body via the bloodstream, water moves through a plant’s
body in a continuous stream, entering through the roots, crawling up
the stem and evaporating out through little openings, or stomata, in
the leaves. In fact, the upward tug of evaporation is what pulls more
water up from the soil, as the clingy water droplets follow each
other skyward through the hollow capillaries of the plant’s stem and
leaves, shinnying as high as 300 or 400 feet above ground in the case
of the giant redwoods.
No, there’s no rest for the weary, especially if you’re immobile.
Beyond feeding style, perhaps the biggest discrepancy between animals
and plants is that animals can move, but plants are of necessity
stuck in place. Unable to defend themselves by running away, plants
have instead become crackerjack chemists, evolving a vast
armamentarium of insect repellents, fungicides, microbicides,
ultraviolet blockers and other defensive compounds that human
chemists have just begun to tally.
Rootedness also complicates a plant’s love life, which brings us back
to the blooming bounty of spring. Plants, like everybody else, want
to spread their seed around and diversify their genetic stock through
sexual reproduction, but it’s hard to meet fresh faces when you don’t
have legs. A number of plant species like pine trees, oaks,
cottonwoods and grasses rely on wind to blow their pollen around,
with the hope that some of the male sperm contained therein will land
on receptive female parts of their far-flung kind. Or if not the same
kind, at least something in the same general group: the boundaries
between plant species are far more porous than they are in animals,
and different species and even genera of plants cross-hybridize with
each other surprisingly often.
Nevertheless, wind sex is highly iffy and inefficient, and many
species of modern plants, the angiosperms, instead manipulate members
of the animal kingdom to serve as yentas in a more discriminating
style. The plants offer up brilliant blossoms to entice a specific
pollinating insect or bird, which gets drunk on the blossom’s nectar
and wants more and so seeks out other blossoms of similar shape,
color or scent. And as the bee or hummingbird flits from one favored
flower to the next, it incidentally delivers pollen pockets to just
the right spots. “We say, isn’t that beautiful, but the precise forms
and shapes of flowers are adaptations to attract individual
pollinators,” Dr. Raven said. When we eat, we are parasites on the
foundational labor of plants; and when we “say it with flowers,” we
are plagiarists, too.