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In 2011, the only place you could buy a pound of pot online was Silk Road, an illegal marketplace labeled by the media as the “Amazon of drugs.”

In 2015, there’s a website run by veteran commodity traders where Colorado growers and retailers can trade cannabis online – legally.

The Denver-based company Amercanex launched its online marketplace last summer, and it has plans to expand outside of Colorado by the end of 2015.

Retired Silicon Valley engineer Angelo Mallol, 56, turned out Sunday for a seminar on how to start a small business – in the pot trade.

He asked questions as instructor Gerry Bedore of the Cannabis Career Institute spoke about emerging opportunities for entrepreneurs wanting to enter California’s medical marijuana market and cash in on a likely 2016 state ballot initiative to legalize recreational pot use.

The Cannabis Career Institute, founded by a Los Angeles marijuana activist and pot deliveryman known as “The Cannabis Warrior,” held a daylong Sacramento program on how to open cannabis businesses, from niche bakeries and organic gardens to marijuana distribution services.

A recent report by The Arcview Group showed that legalized marijuana is now the fastest growing industry in the U.S., posting a whopping 74% growth rate in 2014. Despite a widespread movement to legalize marijuana for both medicinal and recreational purposes across the country, though, the industry still faces some serious challenges on the legal front that investors need to understand. 

So, to give investors a deeper look at some of the more pressing legal issues, I spoke with a leading expert on medical marijuana, Aaron Lachant -- an attorney with the healthcare specialist law firm Nelson Hardiman LLP.

DENVER — While federal law makes their entire industry illegal, many marijuana store owners, growers and retailers fear something completely different: Big Tobacco.

Today, most legal recreational marijuana operations are small, limited to a single state and barred from ever getting large by regulators who want to keep a close eye on the fast-growing industry. But those small operators struggle to get bank loans for expansion, often produce an inconsistent product and sometimes have no idea how to balance supply and demand for their crops.

A marijuana institute in Natick is trying to attract a new crop of students by offering them scholarship funds to cover a portion of their tuition fees.

From now until April 20 — or 4/20 — any new students who enroll at the Northeastern Institute of Cannabis will not only qualify for a $420 scholarship, they will also be entered into a drawing for a chance to win a full ride at the marijuana-centric learning center.

The initial deposit to take classes at the school is also being scaled back, from $700 to $420, in celebration of the number that bears symbolic meaning for marijuana users. The usual total cost of the program is $1,500.

The Uber of medical cannabis delivery has arrived, and the venerable accelerator Y Combinator has given its rubber stamp of approval. Meadow, a San Francisco-based startup, allows card-holding medical marijuana patients to browse different types of cannabis from nearby dispensaries and place an order, and within an hour the goods will be delivered to the patient's door.

If you don't have a medical marijuana card, you can schedule an in-home consultation with one of the doctors Meadow has partnered with and get a recommendation to use medical cannabis.

The popular explanation for medical marijuana dispensaries that have popped up in states from Washington to New York is that marijuana is a wonder drug — treating not just nausea and lack of appetite, but also pain, anxiety, epileptic seizures, and the symptoms of multiple sclerosis and schizophrenia.

The federal government refuses to allow people to use it, proponents say. 

The story, however, isn’t quite so simple.

At the beginning of 2014, when Colorado became the first state to allow the sale of marijuana for recreational use, the whole world was watching. “It was insane,” says Toni Fox, owner of Denver’s 3D Cannabis Center, where the first sale happened. “On January 1, there were close to 200 reporters here. Controlled chaos. It was just packed with reporters.”

But the more successful Colorado’s model is and the more imitation it inspires, the less attention it will get. “Colorado is not going to be the top dog for much longer,” says Kayvan Khalatbari, co-owner of the Denver Relief dispensary. “I think it’s only a matter of time before Colorado really gets overlooked.”

In “Weed the People,” Bainbridge Island author Bruce Barcott delivers a thorough and entertaining survey of the burgeoning legalization of marijuana in the U.S. Barcott appears April 15 at Seattle’s Elliott Bay Book Co.

‘Weed the People: The Future of Legal Marijuana in America’ by Bruce Barcott Time, Inc., 400 pp., $22.95