April 25, 2008

What Darwin Saw Out Back

IN 1860, while studying primroses in the garden of Down House, his home in Kent, England, Charles Darwin noticed something odd about their blooms.

While all the flowers had both male and female parts - anthers and pistils - in some the anthers were prominent and in others the pistils were longer. So he experimented in his home laboratory and greenhouses, cross-pollinating some plants with their anatomical opposites. The results were striking.

"He determined that if they cross-pollinate, they produce more seed and more vigorous seedlings," said Margaret Falk, a horticulturalist and associate vice president at the New York Botanical Garden. The variation is evolution's way of increasing cross-pollination, she said.
Now the Botanical Garden is replicating this work, and more of Darwin's Down House experiments, in a stunning, multipart exhibition called "Darwin's Garden: An Evolutionary Adventure."

In all, the tour is 33 stops, spread throughout about half of the garden's 250 acres. Visitors who enter the exhibition through the Enid A. Haupt Conservatory will encounter a replica of a room in Darwin's house, designed so they can look through the window, as he did, to a profusion of plants and bright flowers: hollyhocks, flax and of course primroses, what Todd Forrest, the garden's vice president for horticulture, calls "a typical British garden." On a table stands a tray holding quills, brushes, sealing wax and tweezers, the kinds of simple tools Darwin used to conduct his world-shaking research.

Darwin grew the flowers not just for their own sake, Mr. Forrest said, but as subjects for observation and experiment, work he carried out in his home laboratory and greenhouses, on workbenches like those in the exhibition. The work displayed on the benches is typical of studies Darwin made of pollination, how plants grow, even what happens when a carnivorous plant devours an insect. Orchids on display remind visitors of the varieties Darwin studied, and how his observations and dissections of their blooms led him to conclude that particular species were pollinated by particular species of insects, a conclusion later research confirmed.

The exhibition also includes a "tree of life" map that guides visitors to the garden's plants and describes where they fit in the natural scheme of things; books, drawings and notes, some in Darwin's own hand; and an interactive exhibit for children.

It anticipates two Darwin anniversaries next year - his 200th birthday and the 150th of his world-changing book, "The Origin of Species."

Though most people associate that book and Darwin's ideas generally with his voyage to the Galápagos and his study of finches there, his work with plants was far more central to his thinking, said David Kohn, a Darwin expert and science historian who is a curator of the exhibition.

Even in the Galapágos he focused on plants, said Dr. Kohn, who is general editor of the Darwin Digital Library of Evolution at the American Museum of Natural History. "He did not even label the finches," he said. "He was fascinated by plants," particularly the way their variation and sexual reproduction challenged the idea that species were stable, a key idea in botany at the time.

As Dr. Kohn writes in the exhibition catalogue, "plants were the one group of organisms that he studied with most consistency and depth over the course of a long scientific career" of collecting, observing, experimenting and theorizing. But Darwin studied more than flowers. He was intrigued by what Dr. Kohn calls the "behavior" of plants - how they move, respond to light, consume insects and otherwise act in the world.

So another exhibit in the Garden conservatory replicates Darwin's studies of climbing plants. Mr. Forrest said Darwin studied plants whose roots move along walls, whose stems twine, whose tendrils curl around other plants and which climb as their leaves grow into tendrils. Visitors who stop to ponder this display will also be able to see, in the garden library, the wispy, primitive drawings Darwin made as he studied plant movement and insect eating. Dr. Kohn said the drawings, which remind him of time-lapse photography, are among his favorite items here even though, as he noted, "Darwin was a terrible drawer."

In his orchard at Down House, Darwin established a "weed garden" by clearing a patch of sod and tracking the germination and growth of every seed that sprouted there. The Botanical Garden has done much the same thing with a small patch in the conservatory.

Most seedlings in Darwin's weed garden vanished, Ms. Falk said, losses he attributed to slugs. ("That's a gardener for you," Mr. Forrest said, "always complaining about something.")

The work Darwin carried out in his gardens, greenhouses and home laboratory is particularly impressive, Ms. Falk said, given that he was limited to a simple microscope and equipment like "quills, matchsticks, bits of wire."

"It was really in his own garden that many of his ideas came together," she added.

As visitors walk through the Botanical Garden they will be able to follow an illustrated maps of the tree of life - the plant part of it, anyway - that tell them where the plants they can see fit in the evolutionary framework.

In the garden's LuEsther T. Mertz Library, they will encounter what Jane Dorfman, its exhibitions coordinator, calls "treasures": some on loan from Cambridge University, where Darwin studied, some from Harvard and some the fruit of what Dr. Kohn called "rummaging" in the garden's extensive collection of Darwiniana. Among them are Darwin's notes from university botany class, a plant specimen he collected on the Galápagos and his preliminary sketch of the tree of life with his note, "I think," at the top.

The gallery also displays his "Experiment Book" with notes and drawings of experiments he carried out in his garden, and studies of flowers that led him to predict - accurately - what kind of bird or insect would pollinate them.

Nearby is Darwin's 1857 letter to Asa Gray, the American botanist who was a major supporter, in which he laid out, one by one, the ideas he would shortly turn into "The Origin of Species." Among other things, Dr. Kohn said, the letter is notable because it "proves Darwin's priority" by demonstrating that it was he, and not his fellow naturalist Alfred Russel Wallace, who developed the theory first.

"It shows he's got it," Dr. Kohn said.

The tree of life exhibits, comprising an unusual mix of living plants, laboratory expertise and historical documents, show that many plants are surprisingly close relatives of others that seem quite different, a concept that helps botanists when they look for likely sources of useful plant chemicals or worry about maintaining biodiversity.

For example, "squashes and oaks are related," said Dennis W. Stevenson, the garden's vice president for laboratory science. "Who'd a thunk it?"

But while many branches move off simply and neatly in ways botanists understand - they are "totally resolved," Dr. Stevenson said - other evolutionary branchings occur in clumps called polytomies, areas where the family history of plants is still unknown.

One major polytomy involves cycads, like palm trees (of which the garden has an unusually large collection), and conifers, like pine trees. Dr. Stevenson is among researchers working with the support of the National Science Foundation to unravel this evolutionary mystery. So far, he said, researchers have come up with two possible explanations. Although they contradict each other, "I like them both," Dr. Stevenson said.

Garden officials recognize that there are those who challenge Darwin's ideas, but for them there is nothing controversial about them. "Our whole science is based on evolution," Gregory Long, the Botanical Garden's president, said, as he surveyed the team of horticulturalists installing the flowers that replicate Darwin's experiments.

"It's the heart of our science," he said. "We wouldn't be here if it hadn't been for Darwin."
"Darwin's Garden: An Evolutionary
Adventure" opens Friday and runs through June 15 at the New York
Botanical Garden, Southern Boulevard and 200th Street, Bedford Park, the Bronx; (718) 817-8700,