MUSEUMS

Spiny oasis of the desert

In the dry Sonoran, animal life revolves around the succulent saguaro cactus       

By Tim Folger 

Arizona-Sonora Desert Museum

2021 N. Kinney Road, Tucson, Arizona

www.desertmuseum.org

A clay pot containing what seems to be nothing but pebbles rests on a counter near the open-air entrance to the Arizona-Sonora Desert Museum. The nondescript pot is worth a close look, for within it are lessons about the tenacity of life and the emergence of beauty in unexpected places.  Scattered among the reddish-brown pebbles are several tiny green nubs, none more than a fraction of an inch high. These, a museum volunteer says, are five-year-old saguaro cacti. When mature—a long, dry century from now—they could stand up to 50 feet tall, and each will hold as much as eight tons of water, liquid life sequestered over decades in a region that sometimes sees only two inches of rainfall annually.

A forest of saguaros stands sentinel around the mountain-ringed museum, which is located just west of downtown Tucson and east of the Tohono O’odham Indian Reservation. A couple of aviaries and some animal enclosures lie within walls, but most of the museum—the best part—is framed by nothing more than rock and sky. Two miles of trails loop through the 21-acre site, providing a glimpse of the mountain lions, bighorn sheep, beavers, bats, and owls that scrabble a living in the vast Sonoran Desert, which covers some 100,000 square miles in the United States and Mexico. Bristly javelinas, a species of peccary that shares a distant ancestor with pigs, root about in ravines alongside the trails, and the occasional five-inch-long hairy tarantula skitters across the path.

These animals and plants may seem to lead separate lives, but their existence is intricately intertwined. Saguaros, for example, need more than water to survive. They do not self-pollinate, so they must rely on birds, bats, and insects to ferry pollen to and from other cacti in order to reproduce. (A sign along the trail notes that 75 percent of all agricultural crops require insect or bird pollination, a reminder that we are no less dependent on them than is the saguaro.) The animals in turn can’t live without the giant cacti, perhaps the desert’s most reliable source of food and shelter. The pollinators feed on the nectar of the cacti, and later, on the three-inch-long green saguaro fruits that ripen just before the autumn rains. Doves, woodpeckers, and flickers—foot-long birds with bright yellow underwings—bore small nests in saguaro trunks.

Other desert pollinators flit along the trail: assorted butterflies, hummingbirds, and bees. Some of the butterflies feed not only on nectar but on the desert itself. After a rainfall, male butterflies—who taste with their feet—slurp up minerals in mud, obtaining nutrients that they pass to females in a sperm packet that can equal about 10 percent of the male’s body weight. A netted enclosure houses dozens of hummingbirds, each of which draws nectar from about 1,000 flowers to supply the 10 or so calories that they burn each day. A human being with a hummingbird’s metabolism would need about 300 pounds of food and 150 gallons of water daily.

The Desert Museum abounds with glories all year round but is particularly inviting in May or June, when the saguaros flower. A single saguaro may produce as many as 200 creamy three-inch-wide flowers, but only a few bloom after sunset on any night—and only for one night. Even if they are not pollinated, the flowers will close forever the next day. Thanks to their reservoirs of water, though, each cactus can produce flowers—even during droughts—every year of its life, which can last up to two centuries. Compared with this rich and near-rock-like persistence, the nearby city of Tucson, with its swimming pools and water-greedy golf courses, seems to be an unsustainable fantasyland. One can’t help but wonder how much longer it will all last.

Finding Sellaio:

Conserving and Attributing a Renaissance Painting 

Cantor Arts Center, Stanford University

www.stanford.edu/dept/ccva

Through November 28, 2004

With the aid of computed tomography, or CT, scan conservators at Stanford University’s Cantor Arts Center have given the Virgin Mary a face-lift. Commandeering the services of the university’s medical center, they zapped The Virgin, Child, and St. John, a Renaissance painting dating to about 1480, with rotating X-ray beams in a CT scanner. By digitally manipulating the three-dimensional images that emerged, the conservators could observe how deathwatch beetle larvae had tunneled through the painting’s four poplar boards, even as they avoided a cheese-based glue that bound the boards together. The scan formed part of a three-pronged prerestoration radiological analysis that included bombardment with ultraviolet rays (above right). Because pigments and varnishes fluoresce differently under UV light, the technique exposed previous retouching attempts. Finally, infrared imaging helped settle a dispute over the identity of the painting’s creator by revealing hatch marks beneath the surface paint—a characteristic of the Florentine artist and Botticelli classmate Jacopo del Sellaio.

—Chloe Veltman