In 1857, Charles Darwin staked out a two-by-three-foot patch of ground in his orchard, cleared away all the grass and other plants, and fenced it off. Then he waited, watched, and took notes.
Any gardener can predict what happened next: the rectangle of bare earth soon sprouted seedlings — of weeds. This little plot, which Darwin called his “weed garden,” was a testing ground for the principle of natural selection, one of the key mechanisms in his theory of evolution.
Darwin’s home gardens – and the meadows, bog, and orchard surrounding Down House, his estate in Kent, England – composed his field station for the botanical research he pursued before and after the publication of "Origin of a Species by Means of Natural Selection."
The gardens yielded lovelier and more useful plants than scrappy weed seedlings, as demonstrated by the representative flower beds, kitchen garden, and orchard re-created in "Darwin’s Garden: An Evolutionary Adventure," an exhibition at The New York Botanical Garden (through June 15).
In the botanical garden’s Haupt Conservatory, brilliant spires of hollyhock, delphinium, and larkspur surround a partial replica of Darwin’s study at Down House. Visitors approach the structure on a facsimile of the “sandwalk,” well known to Darwin scholars, on which the naturalist strolled and pondered questions posed by the curve of a stem or a flower’s distinctive form.
In his study, equipped with a microscope and a camera, he dissected flowers like the surgeon he had once aspired to be. He was searching for the mechanisms that familiar plants used to function and survive. What cellular processes caused them to bend toward the light? What happened when they “slept”? What drew a bee to one flower, a hummingbird to another?
Although his garden laboratory had yielded insights that formed the basis for many of the arguments expressed in "Origin," he plunged back into botanical research immediately after its publication, to further refine and test his ideas. “In the growing season of 1860 ... Darwin threw himself into his botanical experiments,” says David Kohn, a Darwin historian and professor emeritus at Drew University, who curated the exhibition.
“That summer, he was focused on primroses, orchids, and carnivorous plants,” says Dr. Kohn, who also is the general editor of the Darwin Digital Library at the American Museum of Natural History in New York.
Fascinated with a carnivorous bog plant so tiny that it could be cupped in a man’s palm, Darwin fed it unlikely “foods” — egg white, cinders, bits of wood, even chloroform — seeking to understand why it had developed its ability to feed upon insects, and what caused it to close its sticky trap.
A display of the delicate plant – and similar ones of orchids and primroses, which also consumed Darwin’s attention that summer – let visitors explore the big ideas that arose from these experiments.
And they were big ideas. “Flowering plants threw a wrench into the idea of creationism,” the reigning doctrine of the day,” Kohn explains. Creationism held that the number of species was fixed and unchanging, since all forms of life had been created at the same point in time. But scientists of Darwin’s day were chafing against the discovery of countless plant varieties, or variations within species, that creationism could not explain.
Cross-fertilization, the mechanism that produced such diversity, also remained a mystery before Darwin’s botanical experiments, because scientists did not believe that plants could cross-pollinate.
"In six weeks during that marvelous summer of 1860, he figures out the anatomy of all local orchid species,” Kohn says. “By the end, he is able to not only show that cross-fertilization happened and produced different varieties, but he also could predict what the pollinator for each variety would look like, based on the flower shape.”
This breakthrough supported Darwin’s argument that adaptation occurred through natural selection.
Another round of experiments, this time with members of the primrose family, allowed him to see that some adaptations guarantee cross-fertilization to maintain genetic diversity.
The exhibit also includes a display of related documents and artifacts at the botanical garden’s Mertz Library. Here, botanical prints, herbaria pages, and other artifacts chronicle what Kohn calls Darwin’s “journey of the mind.”
The library exhibit illuminates Darwin’s long love affair with plants, not only as experimental subjects and objects of enthralling beauty, but as examples of nature’s greater process: “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”
"Darwin’s Garden: An Evolutionary Adventure" also includes an interactive children’s exhibit (through June 28) in The New York Botanical Garden’s Everett Children’s Adventure Garden, and a self-guided walk through the plant collections represented in Darwin’s evolutionary Tree of Life.
For more information, see http://www.nybg.org/darwin.
Herbariums: timeless means of preserving plants
In 1829, when Charles Darwin began studying botany at Christ's College in England,
his professor used dried specimens of plants, pressed between sheets of paper, to record the identifying characteristics of particular plants.
Each page, known as an herbarium sheet, represented an entire plant (or pieces of larger plants) in all phases of its life cycle. Field notes, including when and where the plant was taken, completed the record, the best means of preserving and documenting specimens at the time.
As it turns out, it still is. Even in the digital age, collecting plants in the field has changed little since the 16th century, when the first known European herbariums were compiled. "What we do here is comb the world to catalog plant diversity, and we do it with dried specimens, just like the old herbaria," says James Miller, dean and vice president for science at The New York Botanical Garden.
In his office, he pulls open a file drawer and plucks out a sheet showing a specimen in the borage family. "We have 7.3 million of these here, in the Steere Herbarium."
Despite modern botany's reliance on this traditional technology, scientists make use of the Internet to share specimen data around the world. The botanical garden's Virtual Herbarium's digital collections, for instance, contain about 1 million herbarium specimens and 120,000 high-resolution images-accessible to anyone, at anytime, for free.
Dip into the data at www.nybg.org.