How an Evolutionary Garden Grows
The man with whom Darwin walked, and his botanical legacy.

The Wall Street Journal, Thursday, May 7, 2009

CAMBRIDGE, England--This year marks the bicentennial of Charles Darwin, who revolutionized our understanding of life's origins. Listen to John Parker, though, and you almost wonder if we're celebrating the wrong man: "Darwin was an indolent, beetle-collecting, drinking, gourmandizing nobody." He was studying divinity at Cambridge University when John Stevens Henslow, a professor of mineralogy and botany, awakened his interest in natural history. "Henslow spotted something extraordinary in Darwin," Mr. Parker says. "He created somebody who was able to think. . . . Without Henslow, there would have been no Darwin."

Henslow himself had begun his research in botany in the 1820s, before Darwin arrived at Cambridge. As Mr. Parker explains, "The major consideration of the day, according to Henslow, was, What is the nature of species?" This, of course, is the question that became Darwin's life work. Henslow would invite the public on "rambles" around Cambridge to examine and collect local flora. As a student, Darwin participated so regularly that he became known locally as "the man who walks with Henslow." It was Henslow who recommended Darwin to the captain of the HMS Beagle, the ship from which he conducted his famous biological surveys of South America.

Henslow left another legacy: the Cambridge University Botanic Garden, which he established in 1831 to grow trees and other plants for research and teaching. Mr. Parker is now the garden's director. On a rainy spring afternoon, he led a group of journalists, visiting for a Templeton Fund conference, on an hour-long ramble of our own.

The centerpiece of the 40-acre garden is its 1,500 trees of 1,000 different species. Just inside the main gate is a giant redwood, "probably the biggest organism that's ever existed on the face of the Earth," says Mr. Parker. Two more stand some 600 feet away, at the other end of the garden's Main Walk. The redwoods here look a lot smaller than the ones I remember from a childhood trip to California's Sequoia National Park, and Mr. Parker explains why: "These are babies. These are only 150 years old. They're about 120 feet in height"--one-third as tall as a full-grown redwood. "The oldest one we know is 3,500 years old, so at 150, this is still in its nappie stage."

The Main Walk, the only straight line in the garden, showcases the coniferous (cone-bearing) trees, including pines, cedars and spruces. On either side are curved paths with flowering trees: chestnuts, maples, poplars. Each genus of tree is planted in clusters of different species or subspecies, showing both continuity and variety--for example, cedars from Lebanon, Morocco and the Himalayas. "They're arranged in a particular order, and they're arranged in families," Mr. Parker tells us as we stroll along one of the paths.

That order was set out in a book by Swiss botanist A.P. de Candolle. Mr. Parker explains how this works when we stop in the Systematic Bed, which holds 1,600 species from 100 families of herbaceous plants, divided into groups according to de Candolle. Mr. Parker shows us how one group is arranged: "[Henslow] took the first page of that group--and it's the buttercup family, Ranunculaceae--put it in, in the far corner of his particular quadrant here, turned the pages, and you work your way all the way round. The last page of the entire book is an American family called the Phytolaccaceae, the pokeweeds, which is on the opposite side of the hedge from the buttercups. So you've gone all the way round the book and you've come back where you started."

He adds: "There's nowhere else where a book has been translated onto the ground in this way. . . . Everything Henslow did, he did for art as well as for science."

The beds are replanted annually, and new trees are added each year too. "The garden never looks like a decrepit 19th-century garden, which many of them in this country now do," Mr. Parker says proudly.

Cambridge is not necessarily the ideal location for a botanic garden. As we stand amid the maples, Mr. Parker says those trees are "quite difficult for us to grow, because they tend to require an acid soil. This is a terrible soil, because it's really chalky, very calcareous, and it's not good for plant life of any sort."

If modern agriculture can compensate, Henslow's heirs aren't interested: "We do not dig if we can avoid it, we do not fertilize, we do not water, we do not spray. The plants either survive or die," Mr. Parker says. "The reason that these trees look so good . . . is that these are the survivors. They will survive under our conditions. . . . You grow them tough, they'll stay tough."

In case anyone hasn't gotten the point, he adds, "This is an evolutionary garden. What would you expect us to do?"

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