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SAN FRANCISCO — On Thursday night, San Francisco’s Exploratorium celebrated a simple question: Is there a more controversial plant than cannabis?

Controversy aside, California’s marijuana counterculture is blooming. So much so that the Exploratorium — a family-friendly “learning laboratory” — dedicated an entire evening to weed during the event, appropriately titled “After Dark: Cannabis.”

“After Dark” nights occur each Thursday at the Exploratorium from 6 to 10 p.m. The events, aimed at the 18-and-older crowd, combine learning, scientific exploration and cocktails — and they always explore one central topic.

“We had one with the theme ‘Teeny Tiny.’ That was fun — looking at scale. And one called ‘Illusions,’ where we looked at all sorts of optical illusions,” Emma Bailey, the Exploratorium’s project manager, said. “The variety is always nice.”

Lead public coordinator Herbie Harman added that “Sexploration,” an event that dove into the biology of sex, “was pretty cool.” Harman is also excited for next month’s installment, “May the Fourth Be With You.” 

“I’m a fan of physics,” the overall-donning public coordinator explained.

“May the Fourth Be With You” will draw “a different crew,” Bailey believes. The “Cannabis” attendees are also “a little bit different than the usual,” she added.

  • Visitors take photos of photos taken by photographer Ofelia Chang of Stock Pot Images, during the exhibit "After Dark: Cannabis" at the Exploratorium in San Francisco, Calif., on Thursday, April 6, 2017. (Ray Chavez/Bay Area News Group)

Indeed, dreadlocks and rainbow-colored highlights were on full display under the exhibit hall’s fluorescent lights. Guests chatted about cannabis cough syrup and their efforts to combine weed and feminism. New friendships quickly formed, catalyzed by a common interest in marijuana.

Local cannabis experts hosted seven unique presentations throughout the evening in addition to April’s seven ongoing weed-centric exhibits. The American Civil Liberties Union discussed criminal justice reform and the racial disparities in arrests and prosecutions while Dr. Donald Abrams, the head of oncology at San Francisco General Hospital, talked about treating pain with cannabis. Other representatives discussed growing and dissecting marijuana and developing hemp-based sustainable building materials.

“We work really hard to bring the best experts,” Harman said.

Dan Grace, founder and president of Dark Heart Nursery in Oakland, and his young assistant, Ellen Ehrenfried, are two of them. Their presentation series, called “Propagation Techniques,” was one of the most popular throughout the evening.

Marijuana differs from many conventional plants because it isn’t propagated with seeds, Grace explained to his attentive audiences.

“We like to have a nice, uniform crop with high-quality genetics, and we do that by reproducing plants asexually,” he said.

The process is akin to cloning sheep. In both cases, only females produce offspring.

“This is a mom,” Grace said, gesturing to a large potted plant on the counter in front of him. “Cannabis is an amazing plant. They call it weed for a reason. This plant loves to grow. And it is resilient.”

As Grace talks about marijuana reproduction, Ehrenfried cuts stems from “Mom” and places them into a flowerpot.

In their Oakland lab, she dips the trimmings in a pest-reducing soapy solution and gives the trimmings hormones that help them take root. From there, Ehrenfried gently places the stems into a fiberglasslike block made of volcanic rock, which has the desired balance of air and water for root development, Grace explained.

Grace doesn’t kid about weed’s ability to grow like, well, a weed. Within a couple of months, a plant grows from a baby to an adult that’s ready for cultivation, said Ehrenfried, a recent plant science graduate from the University of Tennessee.

“Flower Dissection,” a presentation delivered by the Exploratorium’s Gaily Ezer, was arguably as popular — and equally as educational — as “Propagation Techniques.”

As an Exploratorium field trip explainer, Ezer is used to talking to large audiences. And as a hobbyist botanical illustrator, she knows flowers. But Ezer have never given a marijuana dissection presentation until Thursday night.

She took on a comparative approach: “What are some things you notice about this flower?” Ezer asked the audience as she held up a yellow lily.

“Petals! Shapes! Different colors! Stamens!” the audience shouted.

“Yeah, flowers have different signals they use when they want to get laid, basically. You don’t see any of that with this flower,” she said as she lifted up a Mason jar full of weed.

Most flowers — like humans — strive for genetic recombination. In wild, uncontrolled conditions, offspring that are half one parent and half the other have the best genes for survival.

But flower have neither legs nor “After Dark” events. They can’t stroll or mingle with a potential match, so they rely on “flying, fuzzy little things,” such as bees, to do their dirty work.

Bees “are like toddlers,” Ezer said. “They’re not clean eaters.” While some pollen ends up in bees’ digestive tracts, the rest ends up elsewhere.

“The point is to get one plant’s pollen into another plant,” she said.

Marijuana is radically different — we prevent it from mating.

“In marijuana, there are two sexes. One plant has one sex. Most of you have only seen female flowers,” Ezer said. Cannabis has dramatically changed since the plant was originally illustrated about a century ago, she adds.

“We’ve done so much selecting and propagation. We’re trying to get plants that are unfertilized. We don’t like seeds.”

And of course, human selection has altered weed’s natural chemistry. Under natural circumstances, cannabis doesn’t need as much THC — its well-known psychoactive component — and CBD — a calming one — to grow. “That was totally us,” Ezer said, laughing.

California is invested in marijuana, perhaps more so than other states, said Linda Delair, a green building consultant and hemp expert. But, despite marijuana’s ability to treat pain and hemp’s use as an eco-friendly building material, cannabis is “still considered a Schedule 1 narcotic,” Delair said.

Delair is hopeful this will change. She believes small farms will begin growing both hemp and marijuana again. And, undoubtedly, cannabis has its group of loyal followers.

Of the approximately 4,000 “After Dark: Cannabis” attendees, Exploratorium volunteer Pras Krishnan believes the vast majority use the drug. “I think you can count on one hand those that don’t,” he said as he surveyed the room full of bobbing man buns.

“Every month brings a different kind of audience,” Harman, the lead public coordinator, added. “Everyone here tonight was so sweet. You can tell there’s a deep culture around cannabis.”